{"site":"https://digitalgemology.com","build":"20261101-105320","index":"https://digitalgemology.com/learn","lessons":[{"id":"4C-L1","course":"The four Cs","lesson_number":1,"title":"The 4 Cs of diamonds explained: carat, color, clarity and cut","url":"https://digitalgemology.com/learn/four-cs/the-four-cs-explained","path":"/learn/four-cs/the-four-cs-explained","markdown":"https://digitalgemology.com/learn/four-cs/the-four-cs-explained.md","summary":"The 4 Cs of diamonds: color (D to Z), clarity (FL to I3), cut (Excellent to Poor) and carat weight. What each scale means and how a lab grades it.","queries":["4 cs of diamonds","what are the 4 cs","diamond grading"],"quiz":"https://digitalgemology.com/skool/quiz/the-four-cs/what-the-four-cs-are","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":[],"text":"[The four Cs of diamonds](https://digitalgemology.com/learn/four-cs) · 3 min read\n\n# The 4 Cs of diamonds explained: carat, color, clarity and cut\n\nThe four Cs of diamonds are color, clarity, cut and carat weight, four scales that GIA made into a grading system in the 1950s. Color goes from D to Z, clarity has 11 grades from FL to I3, cut goes from Excellent to Poor, and one carat is 200 mg.\n\n## What does \"blue white\" mean?\n\nUntil the middle of the twentieth century, nobody could tell you. People described diamond color with loose letters like A, B and C, with numbers or with Roman numerals. They also used phrases like \"gem blue\" and \"blue white\". Two jewelers could use the same word for different stones.\n\nThe four Cs fixed that. They turned the quality of a diamond into four scales that mean the same thing everywhere.\n\n## Four scales, one language\n\nRobert M. Shipley, a former retail jeweler, founded GIA. He put diamond quality into four groups and gave them a name that is easy to remember: **color, clarity, cut and carat weight**. In the 1950s GIA made them into a grading system. Today the whole world uses it.\n\n- **Color** goes from **D**, colorless, to **Z**, light yellow or brown. The scale starts at D on purpose, so that nobody could confuse it with the old A, B and C.\n- **Clarity** has **11 grades**, from **Flawless (FL)** to **I3**. A grader judges it at 10x magnification.\n- **Cut** goes from **Excellent** to **Poor**. GIA gives a cut grade to standard round brilliants only.\n- **Carat weight** is the weight of the stone. One carat is 200 milligrams, and it has 100 points.\n\nTrained eyes judge three of the four Cs against fixed standards:\n\n- **Color:** the grader compares the stone with a set of master diamonds under controlled light.\n- **Clarity:** the grader examines the stone at 10x. For color and for clarity, at least two graders work independently.\n- **Cut:** the grade combines measured proportions with a visual check of the finish.\n\nCarat weight is different. The lab simply weighs the stone.\n\nNo single C sets the value of a diamond. All four do, together.\n\n![The simulator's report panel, one control per C, each labeled.](https://digitalgemology.com/img/learn/4c-l1-report-four-cs-controls.webp?v=42940c0c)\n\nThe simulator's report panel, one control per C, each labeled.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the round brilliant in diamond. It starts at the top of every scale: 1 carat, D, FL, Excellent.\n2. Set **Color grade** to **Z**. Look at the stone, then set it back to D.\n3. Set **Clarity grade** to **I3**. Look, then set it back to FL.\n4. Set **Cut grade** to **Poor**. Look, then set it back to Excellent.\n5. Change **Carat weight** from 1 to 2. What changes, and what stays the same?\n\n## What the simulator shows\n\nEach C changes the stone in its own way.\n\n**Color** tints the light as the light travels through the stone. A longer path inside gives more color. So the tint shows most where the light bounces the furthest.\n\n**Clarity** puts crystals, pinpoints and feathers inside the stone. Each one blocks or reflects some light at one spot. The rest of the stone does not change.\n\n**Cut** changes the angles and the size of the **table** (the flat top) and the **pavilion** (the cone underneath). At Poor, more light leaks out of the bottom and does not come back to you. The whole face changes.\n\n**Carat** changes only the size. The pattern stays exactly the same.\n\nThat is why we say that cut is the C that decides how a stone looks. Each C has its own page: [carat weight](https://digitalgemology.com/learn/four-cs/carat-weight-vs-size), [color](https://digitalgemology.com/learn/four-cs/diamond-color-scale-d-to-z), [clarity](https://digitalgemology.com/learn/four-cs/diamond-clarity-scale) and [cut](https://digitalgemology.com/learn/four-cs/diamond-cut-grade-excellent-vs-poor).\n\n## Key points\n\n- The four Cs are color, clarity, cut and carat weight. They are four scales that replaced vague trade words with a shared language.\n- Color goes from D to Z, and clarity from FL to I3 (11 grades). Cut goes from Excellent to Poor (round brilliants only). Carat weight is 200 mg per carat.\n- At least two graders grade color and clarity by eye against fixed standards. The lab weighs the carat weight.\n- Each C changes a stone differently. Cut is the C that changes the whole face.\n\n**Go further:** [carat weight vs size](https://digitalgemology.com/learn/four-cs/carat-weight-vs-size): why a 2 ct stone isn't twice as wide as a 1 ct.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-four-cs/what-the-four-cs-are)\n\n## Keep exploring\n\n- [Next lesson: Carat weight vs size: why a 2 ct diamond isn't twice as big](https://digitalgemology.com/learn/four-cs/carat-weight-vs-size)\n- [Try another topic · Diamond vs moissanite: Moissanite's refractive index, and why it needs its own cut](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-refractive-index-and-cut)\n\n[The four Cs of diamonds: all lessons](https://digitalgemology.com/learn/four-cs) · [All topics](https://digitalgemology.com/learn)"},{"id":"4C-L2","course":"The four Cs","lesson_number":2,"title":"Carat weight vs size: why a 2 ct diamond isn't twice as big","url":"https://digitalgemology.com/learn/four-cs/carat-weight-vs-size","path":"/learn/four-cs/carat-weight-vs-size","markdown":"https://digitalgemology.com/learn/four-cs/carat-weight-vs-size.md","summary":"Carat weight vs size: a carat is 200 mg, and weight grows with the cube of size. So a 2 ct diamond is only 26% wider than a 1 ct, with 59% more face.","queries":["carat weight vs size","diamond carat size chart mm","1 carat vs 2 carat diamond"],"quiz":"https://digitalgemology.com/skool/quiz/the-four-cs/carat-weight","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[The four Cs of diamonds](https://digitalgemology.com/learn/four-cs) · 4 min read\n\n# Carat weight vs size: why a 2 ct diamond isn't twice as big\n\nCarat is weight, not size: one carat is 200 mg. Weight grows with the cube of size, so a 2 ct diamond is only 26% wider than a 1 ct: a 1.00 ct T73 is 6.48 mm across, and a 2.00 ct T73 is 8.16 mm.\n\nVideo: [Why a 2 carat diamond isn't twice as big: carat weight vs size (animated)](https://www.youtube.com/watch?v=ngidqkrLg00)\n\nA cube that doubles its edge holds 8 times as much. So a diamond with double the weight is only 1.26 times as wide, with 1.59 times the face. The T73 at 0.50, 1.00 and 2.00 ct is 5.14, 6.48 and 8.16 mm wide. A stone twice as wide would weigh 8 ct. · 1 min 28 s · No sound, captions on screen\n\n## Transcript\n\nThe 2.00 ct weighs twice as much. How much wider is it?\n\nA carat is a weight, not a size. One carat is 200 mg.\n\nWeight is volume times density. So weight grows with volume.\n\nMake the cube twice as wide, twice as long and twice as deep.\n\nIt holds 8 cubes: 8 times the volume, 8 times the weight.\n\nNow turn it around. Start from twice the weight.\n\nMake it into a cube again. Each edge is only 1.26 times as long.\n\n1.26 is the cube root of 2. Twice the weight is only 26% wider.\n\nFace up, you see area. Area grows with the square of the width.\n\nSo twice the weight shows about 59% more face. Not twice as much.\n\nNow the T73 in diamond, all three at the same scale.\n\nThe 3D Gemstone Simulator gives the width of each one.\n\nFrom 1.00 ct to 2.00 ct: 6.48 mm to 8.16 mm. That is 26% wider.\n\nNow make a T73 twice as wide as the 1.00 ct.\n\nIt must weigh 8 carats: 2 × 2 × 2 times the weight.\n\nWeight grows with the cube of size. Double the weight is 26% wider.\n\n## A quick guess\n\nPicture a 1-carat round diamond. Now picture a 2-carat one beside it. How much wider is the 2-carat?\n\nMost people say \"twice as wide\", or at least \"a lot\". The answer is 26%. A 1.00 ct [T73](https://digitalgemology.com/cuts/t73-round-brilliant) is 6.48 mm across; a 2.00 ct T73 is 8.16 mm. Double the weight buys you less than two millimeters.\n\nHere is why.\n\n![0.50, 1.00 and 2.00 ct side by side at their true sizes, each labeled with its width.](https://digitalgemology.com/img/learn/4c-l2-t73-carat-0.5-1-2.webp?v=5f35f879)\n\n0.50, 1.00 and 2.00 ct side by side at their true sizes, each labeled with its width.\n\n## A carat is a weight\n\n**Carat** measures weight, not size. One carat is 200 milligrams, a fifth of a gram. For smaller stones, the carat has 100 **points**. So a 0.75 ct diamond is a \"75-pointer\", and a half carat is 50 points.\n\nA lab weighs every stone on an electronic microbalance. GIA's microbalance reads to the fifth decimal place, a hundred-thousandth of a carat. The report gives the weight rounded to two decimals. Carat is the only one of the four Cs that the lab measures directly. Nobody's eye is involved.\n\nAnd diamond is rare by nature. GIA says that miners dig about a ton of rock to get less than half a carat of rough diamond.\n\n## Weight grows with the cube\n\nWeight is volume times density. Our 3D models give the volume of every cut, and the density of diamond does the rest. For a cut of a given shape, volume grows with the **cube** of its size. Make a stone twice as wide, twice as long and twice as deep, and it holds eight times as much diamond.\n\nNow turn that around. When you double the weight, you multiply every dimension by the cube root of 2, which is 1.26. That's the 26%.\n\nThe face-up area grows with the square of the width. So the 2 ct shows about 59% more surface than the 1 ct. That's a real step up, and you can see it. It just isn't double.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the T73 Round Brilliant in diamond.\n2. In the report, find **Carat weight**. Click through every step from 0.25 to 5.\n3. Watch the stone on screen. Then watch the **scale bar** under it, and read **Measurements** in the report at each step.\n4. Before you click 5, write down your guess for its width.\n5. **The challenge:** which carat step shows about twice the face-up area of the 0.50 ct? Use the measurements to find it, not your eye.\n\n## What the simulator shows\n\n**The stone didn't grow on screen.** The simulator always makes the stone fill the view, so you can study its pattern at any weight. The scale bar and the measurements show the size. As the carat goes up, each millimeter takes up less of the picture, so the bar gets shorter. From time to time it jumps to a rounder length (0.5, 1 or 2 mm). Read the number on it.\n\n**The measurements follow the cube root.** Here's the T73 in diamond:\n\n| Carat | Diameter | Depth |\n| --- | --- | --- |\n| 0.25 | 4.08 mm | 2.52 mm |\n| 0.50 | 5.14 mm | 3.17 mm |\n| 0.75 | 5.89 mm | 3.63 mm |\n| 1.00 | 6.48 mm | 4.00 mm |\n| 1.50 | 7.42 mm | 4.58 mm |\n| 2.00 | 8.16 mm | 5.04 mm |\n| 3.00 | 9.34 mm | 5.77 mm |\n| 5.00 | 11.08 mm | 6.84 mm |\n\nThe 5 ct has five times the weight of the 1 ct, but it is only 71% wider. To be twice as wide as the 1 ct, a T73 must weigh 8 carats.\n\n**The challenge.** The area grows with the weight to the power two-thirds. So twice the area of the 0.50 ct needs 2.83 times its weight: about 1.41 ct. The nearest step is **1.50 ct**: 7.42 mm against 5.14 mm, so 2.08 times the area. Three times the weight, twice the face.\n\n**Same carat, different size.** Carat sets only the weight. The cut and the material decide how that weight spreads out. In moissanite, the same 1.00 ct T73 is 6.67 mm across, because moissanite is less dense than diamond. And a badly cut diamond hides weight in a deep pavilion and a thick girdle. [Diamond cut grade: Excellent vs Poor](https://digitalgemology.com/learn/four-cs/diamond-cut-grade-excellent-vs-poor) shows this side by side.\n\n## Magic sizes\n\nSome weights sell better than others: half a carat, three-quarters, one carat. Demand makes these round numbers special, not looks. A 0.99 ct T73 is 0.02 mm narrower than a 1.00 ct, and nobody can see that difference. But it is below the 1-carat line, so its price is usually much lower.\n\nPrice doesn't go up in a straight line either. Larger diamonds are rarer and people want them more. So a 2-carat stone costs more than two 1-carats when the other three Cs are equal.\n\n## Key points\n\n- One carat is 200 mg, and it has 100 points. Labs weigh to five decimals and report two.\n- Weight grows with the cube of size. So double the weight is only 26% wider, with 59% more face-up area.\n- The simulator keeps the stone the same size on screen. Read the scale bar and the measurements for its true size.\n- The same carat can face up larger or smaller. The material and the cut decide.\n- Round \"magic\" weights have a price step that the eye cannot see: 0.99 ct is 0.02 mm narrower than 1.00 ct.\n\n**Go further:** the [T73 Round Brilliant cut page](https://digitalgemology.com/cuts/t73-round-brilliant) lists its weight and measurements from the 3D model.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-four-cs/carat-weight)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: The diamond color scale, D to Z: where you first see a tint](https://digitalgemology.com/learn/four-cs/diamond-color-scale-d-to-z)\n- [Try another topic · Diamond anatomy and proportions: Diamond table percentage: what table size does to the light](https://digitalgemology.com/learn/diamond-anatomy/diamond-table-percentage)\n\n[Previous lesson](https://digitalgemology.com/learn/four-cs/the-four-cs-explained) · [The four Cs of diamonds: all lessons](https://digitalgemology.com/learn/four-cs) · [All topics](https://digitalgemology.com/learn)"},{"id":"4C-L3","course":"The four Cs","lesson_number":3,"title":"The diamond color scale, D to Z: where you first see a tint","url":"https://digitalgemology.com/learn/four-cs/diamond-color-scale-d-to-z","path":"/learn/four-cs/diamond-color-scale-d-to-z","markdown":"https://digitalgemology.com/learn/four-cs/diamond-color-scale-d-to-z.md","summary":"The diamond color scale, D to Z: what it measures, its five ranges, how a lab grades color, and how warm light hides the tint between nearby grades.","queries":["diamond color scale","d to z color grade","best diamond color for the money"],"quiz":"https://digitalgemology.com/skool/quiz/the-four-cs/color-d-to-z","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[The four Cs of diamonds](https://digitalgemology.com/learn/four-cs) · 4 min read\n\n# The diamond color scale, D to Z: where you first see a tint\n\nThe diamond color scale goes from D, colorless, to Z, light yellow or brown, and measures how much tint a near-colorless diamond has. Its 23 letters fall into five ranges, and labs grade each stone against master diamonds in standard light.\n\n## Four stones, one question\n\nFour diamonds sit in a row under the same lamp. Same cut, same carat, same clarity. One is a D, one an H, one an N and one a Z. Which is which?\n\nThe Z gives itself away. The N is plainly warm. But the D and the H? Most people hesitate. They are four letters apart on the scale, and on paper that's a big step.\n\nThat hesitation is the whole point. Color grades are real, and they matter for value. But how much you *see* depends on where you are on the scale, and on the light.\n\n![D, H, N and Z side by side under the grading lamp.](https://digitalgemology.com/img/learn/4c-l3-t73-color-d-h-n-z.webp?v=7a17a2d3)\n\nD, H, N and Z side by side under the grading lamp.\n\n## What the scale measures\n\nThe D-to-Z scale measures how much yellow or brown tint a near-colorless diamond has. **D** is colorless. **Z** is light yellow or brown. Truly colorless diamonds are rare: most diamonds in jewelry have a slight tint.\n\nA letter isn't one exact shade. Each letter covers a band of tint, and the tint goes from barely there to plainly visible as you go down the scale. Our simulator puts the 23 letters into five ranges, with the same names as GIA's scale:\n\n- **D–F, Colorless.** The rarest. Even a trained grader can tell them apart only beside master stones.\n- **G–J, Near colorless.** Looks white face up. A slight tint shows beside a better grade.\n- **K–M, Faint.** You can see a faint warm tint face up, most of all in a larger stone.\n- **N–R, Very light.** A yellow or brown tint that is easy to see.\n- **S–Z, Light.** Plainly yellow or brown.\n\nA Z isn't a bad diamond. It's a diamond with a visible tint, and some people choose exactly that warmth.\n\n## How a lab grades it\n\nLight and background change how a diamond looks. So a lab never grades color by eye in a showroom. GIA compares each stone with a set of **master diamonds** of known grade, in a standard viewing environment. At least two graders give their grades independently. More graders can join, depending on how well the first graders agree and on the weight and quality of the stone. The grade stands only when they agree.\n\nThe scale starts at D for a reason that we give in [the four Cs explained](https://digitalgemology.com/learn/four-cs/the-four-cs-explained): GIA wanted a clean break from the vague A, B and C of the past.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the [T73](https://digitalgemology.com/cuts/t73-round-brilliant) in diamond, lighting **Grading lamp**.\n2. In the report, under **Color grade**, pick the range **G–J** and then **H**. Switch back and forth between D and H. Then try N and Z.\n3. **Find your threshold.** Start at D and go down one letter at a time. Do not go back. Write down the first letter where you say \"that's warm\" with no D to compare.\n4. **Change the light.** Set the stone to H, then try **Photo studio**, **Home** and **Restaurant**. Can you still tell H from D?\n5. Set it to Z and go through the same lights.\n\n## What the simulator shows\n\n**Where the tint lives.** The simulator colors the light as it travels through the stone. A longer path inside gives more yellow. Light that bounces around the pavilion several times before it gets to you carries the most color. That's why the tint seems to sit inside the stone, not on its surface.\n\n**Your threshold.** The note in the simulator puts the first tint that you can see face up in the K–M range. Where was yours? In our model, each letter adds a little more absorption than the letter before it. So the steps near D are tiny, and the steps near Z are bigger.\n\n**The light.** The Grading lamp is a neutral daylight lamp. Under it, H looks different from D if you look for it. Warm Home light makes the gap smaller. In the dim, warm Restaurant scene, D and H look the same. The warm light tints every stone, so the faint tint of the stone itself drowns in it. A Z still shows, because its color is stronger than the color of the light. That's why labs grade color under controlled light and against master stones. It is also why you shouldn't judge a G against an H by candlelight.\n\nOne simplification to know: in a real diamond, a larger stone shows its color more easily, because the light travels further inside. Our simulator keeps the color depth the same at every carat. So you can compare grades without the size getting in the way.\n\n## Key points\n\n- The D-to-Z scale measures how much yellow or brown tint a near-colorless diamond has. D is colorless, and Z is light yellow or brown.\n- Each letter is a range. The scale has five ranges: colorless, near colorless, faint, very light and light.\n- Labs grade color against master diamonds in standard light, with at least two independent graders.\n- Color comes from absorption along the path of the light inside the stone. So it collects where the light travels furthest.\n- Warm, dim light hides the difference between nearby grades. Neutral light shows it.\n\n**Go further:** to compare grades, use the Photo studio and the Grading lamp in the [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator). Try your threshold test in both.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-four-cs/color-d-to-z)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Fancy color diamonds and fluorescence: beyond the Z grade](https://digitalgemology.com/learn/four-cs/fancy-color-diamonds-and-fluorescence)\n- [Try another topic · Historic diamond cuts: the history of the brilliant: Hearts and arrows diamonds: precision you can see](https://digitalgemology.com/learn/historic-cuts/hearts-and-arrows-diamonds)\n\n[Previous lesson](https://digitalgemology.com/learn/four-cs/carat-weight-vs-size) · [The four Cs of diamonds: all lessons](https://digitalgemology.com/learn/four-cs) · [All topics](https://digitalgemology.com/learn)"},{"id":"4C-L4","course":"The four Cs","lesson_number":4,"title":"Fancy color diamonds and fluorescence: beyond the Z grade","url":"https://digitalgemology.com/learn/four-cs/fancy-color-diamonds-and-fluorescence","path":"/learn/four-cs/fancy-color-diamonds-and-fluorescence","markdown":"https://digitalgemology.com/learn/four-cs/fancy-color-diamonds-and-fluorescence.md","summary":"Diamond fluorescence: what it is, how common it is, and what it does to the look. Also how a diamond with more color than Z gets a fancy color grade.","queries":["diamond fluorescence","fancy color diamond grades","is fluorescence bad in a diamond"],"quiz":"https://digitalgemology.com/skool/quiz/the-four-cs/beyond-z-fancy-color-and-fluorescence","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[The four Cs of diamonds](https://digitalgemology.com/learn/four-cs) · 4 min read\n\n# Fancy color diamonds and fluorescence: beyond the Z grade\n\nDiamond fluorescence is visible light, almost always blue, that a diamond gives off under ultraviolet light. About 25 to 35% of diamonds show some, it isn't part of the color or clarity grade, and in most diamonds you won't see it in everyday light.\n\n## Lights out\n\nTwo diamonds sit side by side in daylight. Both are D, Flawless, Excellent. In daylight, nobody can tell them apart.\n\nNow switch the room to ultraviolet light. One goes dark. The other lights up an intense blue, as if someone switched it on.\n\nSame color grade. Same clarity grade. That glow is **fluorescence**, and it's one of the two topics of this page. The other topic is a diamond that has too much color for the D-to-Z scale.\n\n![No fluorescence beside very strong fluorescence under the UV lamp.](https://digitalgemology.com/img/learn/4c-l4-t73-uv-none-vs-very-strong.webp?v=8eca5a24)\n\nNo fluorescence beside very strong fluorescence under the UV lamp.\n\n## Past Z: a fancy color\n\nThe D-to-Z scale ends with a master stone at Z. A yellow or brown diamond with more color than that leaves the scale completely. It is then treated as a **colored diamond**. When its color is strong enough, it gets a **fancy** grade.\n\nA fancy color has three parts:\n\n- its **hue** (yellow, orange, blue…)\n- its **tone** (how light or dark)\n- its **saturation** (how strong).\n\nOne intensity word sums them up. Colored diamonds aren't only yellow and brown. They also come in red, pink, blue and green, among others.\n\nHere's the twist that surprises people. On the D-to-Z scale, less color is rarer. Past Z, it turns around: a stronger, purer fancy color is the prize.\n\nOur simulator gives the fancy grades on 28 swatches, from Red through the yellows, greens, blues and purples to Purplish Red, plus Brown. They come from GIA's continuous hue circle. You can set each swatch to five intensities:\n\n- **Fancy Light:** the palest fancy grade, a soft but definite color.\n- **Fancy:** an even color of medium strength.\n- **Fancy Intense:** strong color.\n- **Fancy Vivid:** the strongest, purest color.\n- **Fancy Deep:** strong color, darker in tone.\n\nTwo hues follow a special rule, the same as in GIA grading: red and purplish red get only one grade, Fancy. They are always Fancy Red or Fancy Purplish Red. And in our simulator, brown has only three intensities: Fancy Light, Fancy and Fancy Deep.\n\n## Fluorescence: the hidden glow\n\nSome diamonds give off visible light while ultraviolet light shines on them. They stop at the moment the UV goes off. That's **fluorescence**. A report gives its strength under long-wave UV, from None through Faint, Medium and Strong to Very strong. It also gives its color.\n\nGIA found this across the diamonds it grades:\n\n- About 25 to 35% show some fluorescence.\n- Only about 10% of those are Medium or stronger, the strengths that may change the look.\n- In more than 95% of fluorescent diamonds, the glow is blue. Yellow, white and other colors are rare.\n- In most diamonds, you won't see it at all in everyday light. In GIA's observations, people often liked the look of stones with medium to strong blue better.\n- Fewer than 0.2% of fluorescent diamonds look hazy or oily from extremely strong fluorescence.\n\nFluorescence doesn't make a diamond weaker, and it isn't part of the color or clarity grade. The report lists it as an extra characteristic that helps to identify the stone.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the [T73](https://digitalgemology.com/cuts/t73-round-brilliant) in diamond. Set the lighting to **UV lamp**.\n2. In the report, under **Fluorescence**, step from **None** to **Very strong**. Watch the glow build.\n3. Leave it at Very strong and switch to **Photo studio**, then **Sunny day**. What changed?\n4. Go back to Photo studio. Under **Color grade**, switch the scale from **D to Z** to **Fancy color**. Pick **Yellow** and step through the intensities. Then try **Blue** and **Purplish Red**.\n5. **The challenge:** set a Z. Then find the weakest fancy yellow intensity that looks clearly more yellow than the Z.\n\n## What the simulator shows\n\n**The glow.** The UV lamp is a dark room with only long-wave UV light. Under it, the non-fluorescent stone stays dark. The fluorescent stone lights up blue, and it gets brighter at each step. The simulator adds the glow along each light path inside the stone. So the deeper the light travels, the more it glows.\n\n**In daylight, nothing.** Switch to any daylight scene, and the two stones look the same. That agrees with what GIA found for most diamonds. One simplification: real daylight has some long-wave UV in it. So a real fluorescent diamond does react a little outdoors. The simulator shows the glow under the UV lamp only.\n\n**The fancy colors.** The intensity words go up from a soft Fancy Light to a saturated Fancy Vivid. Fancy Deep makes the color darker, not stronger. Red and Purplish Red give no intensity choice at all, and Brown gives only three. A fancy yellow is a different animal from a Z: its grade is about how much color it has, not how little.\n\n## Key points\n\n- A yellow or brown diamond with more color than the Z master stone leaves the D-to-Z scale. With enough color, it gets a fancy grade.\n- A fancy color has a name made of a hue and an intensity word. Stronger, purer color is rarer and more valued.\n- Fluorescence is visible light that a diamond gives off under UV. A report gives its strength under long-wave UV and its color.\n- About a quarter to a third of diamonds fluoresce, almost always blue. For most of them, it makes no difference to the look that you can see.\n- Fluorescence isn't part of the color or clarity grade, and it doesn't make the stone weaker.\n\n**Go further:** try the same Very strong stone in every lighting scene of the [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator). Find the scene where you think the glow matters most in real life.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-four-cs/beyond-z-fancy-color-and-fluorescence)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: The diamond clarity scale explained, from FL to I3](https://digitalgemology.com/learn/four-cs/diamond-clarity-scale)\n- [Try another topic · Historic diamond cuts: the history of the brilliant: Old mine cut diamonds: tidier, not brighter](https://digitalgemology.com/learn/historic-cuts/old-mine-cut-diamond)\n\n[Previous lesson](https://digitalgemology.com/learn/four-cs/diamond-color-scale-d-to-z) · [The four Cs of diamonds: all lessons](https://digitalgemology.com/learn/four-cs) · [All topics](https://digitalgemology.com/learn)"},{"id":"4C-L5","course":"The four Cs","lesson_number":5,"title":"The diamond clarity scale explained, from FL to I3","url":"https://digitalgemology.com/learn/four-cs/diamond-clarity-scale","path":"/learn/four-cs/diamond-clarity-scale","markdown":"https://digitalgemology.com/learn/four-cs/diamond-clarity-scale.md","summary":"The diamond clarity scale: 11 grades in six categories, from FL to I3, judged at 10x. What decides a grade, and how visible inclusions are to the eye.","queries":["diamond clarity scale","vs1 vs vs2","eye clean diamond"],"quiz":"https://digitalgemology.com/skool/quiz/the-four-cs/clarity","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[The four Cs of diamonds](https://digitalgemology.com/learn/four-cs) · 4 min read\n\n# The diamond clarity scale explained, from FL to I3\n\nThe diamond clarity scale has 11 grades in six categories, from Flawless (FL) to I3, and a grader judges all of them at 10x magnification. The grade depends on the size, number, position, visibility and darkness of the characteristics, not on a simple count.\n\n## Spot the SI2\n\nThree diamonds, side by side. One is Flawless. One is SI2, \"slightly included\", the last grade before the included range. One is I3, the bottom of the scale. Which is which?\n\nThe I3 is easy: dark specks all through it. But the other two? At this distance, most people can't pick the SI2. It looks as clean as the Flawless stone.\n\nNow fill the screen with the SI2 alone, and there they are: small crystals and pinpoints, all through the stone. Graders judge clarity at that scale, under magnification, not at arm's length. Keep those two distances apart. That is the key to this whole C.\n\n![FL, SI2 and I3 side by side.](https://digitalgemology.com/img/learn/4c-l5-t73-clarity-fl-si2-i3.webp?v=bb9a874b)\n\nFL, SI2 and I3 side by side.\n\n![The SI2 filling the frame.](https://digitalgemology.com/img/learn/4c-l5-t73-clarity-si2.webp?v=297707de)\n\nThe SI2 filling the frame.\n\n## What clarity measures\n\n**Clarity** is about the absence of two kinds of characteristics:\n\n- **inclusions**, which are inside the stone\n- **blemishes**, which are on its surface.\n\nDiamonds form under very high heat and pressure. As a diamond grows, small crystals can get trapped inside it. The crystal structure of the diamond itself can also grow irregularly. A diamond with no characteristics at all is extremely rare.\n\nGIA's scale has 11 grades in six categories. A skilled grader judges all of them at 10x magnification:\n\n- **Flawless (FL):** a grader finds nothing at all, inside or on the surface.\n- **Internally Flawless (IF):** clean inside; the only marks are on the surface.\n- **Very, Very Slightly Included (VVS1, VVS2):** inclusions so small that even a trained eye at 10x has difficulty finding them.\n- **Very Slightly Included (VS1, VS2):** small inclusions that take some searching at 10x.\n- **Slightly Included (SI1, SI2):** inclusions that you see quickly at 10x.\n- **Included (I1, I2, I3):** inclusions that are easy to see at 10x. They can make the stone cloudy or reduce its brilliance.\n\nFlawless is strict. A diamond with a few very small polish marks can still get an Excellent polish grade. But those same marks stop it from being Flawless.\n\n## How a lab grades it\n\nThe grader examines the diamond under standard conditions at 10x and finds every clarity characteristic. The grader also looks for clarity treatments, for example fracture filling or laser drilling. At least two graders grade the stone independently. Then they **plot** the characteristics on a diagram of the shape and facets of the stone. This diagram is a map of that diamond.\n\nThe grade isn't a count. It depends on five things:\n\n- the **size** of the characteristics\n- their **number**\n- their **position**\n- how **noticeable** they are in the stone as a whole\n- how **dark or light** they look.\n\nOne dark crystal under the table can matter more than three faint pinpoints near the girdle.\n\nAnd those characteristics are useful. Like birthmarks, they identify one particular stone. They also help gemologists tell natural diamonds from synthetics and simulants.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the [T73](https://digitalgemology.com/cuts/t73-round-brilliant) in diamond, lighting **Photo studio**. Make the stone fill most of your screen.\n2. **Hide and seek.** In the report, under **Clarity grade**, step from **FL** toward **I3**, one grade at a time. Write down the first grade where you can see something at normal viewing distance. Do not zoom in.\n3. At each grade, scroll down the report to **Clarity characteristics**. The diagram plots each characteristic on the crown (left) and the pavilion (right). Read the **Comments** line too.\n4. **The puzzle.** Compare **VVS2** and **VS1**. Both plot two characteristics. Why is VS1 the lower grade?\n5. Turn the stone slowly at **SI2**. Do the characteristics stay equally visible from every angle?\n\n## What the simulator shows\n\n**The diagram.** At FL, the diagram plots nothing. At IF, the report notes \"internally flawless\". Then the map fills up:\n\n- one characteristic at VVS1\n- two at VVS2 and VS1\n- three at VS2\n- one more at each grade below that, up to eight at I3.\n\nIn VVS they are pinpoints only. A crystal joins at VS1, and a feather at VS2.\n\n**The puzzle.** VVS2 and VS1 have the same count. The difference is the type and the size. VS1 adds a crystal, and the simulator sets the size of every characteristic by grade. Size and type matter, not only the number. A real grader thinks like that too.\n\n**What they do to light.** In the simulator, a crystal or a pinpoint stops any light path that hits it. So it shows as a dark spot. A feather is a small break inside the stone. It reflects part of the light, so it can flash bright as the stone turns. When you turned the SI2, characteristics came into view and went out of view as the facets lined up. Visibility depends on the angle and the light. So one look from one side never tells the whole story.\n\n**Your threshold.** The simulator's notes describe VS inclusions as \"seen at 10×, rarely by eye\" and SI as \"noticeable at 10×, and sometimes to the eye\". Where did you first see something? Only a skilled grader at 10x can find many of the inclusions in SI stones. SI is one of the most popular categories: it costs less and is still beautiful.\n\n## Key points\n\n- Clarity grades the absence of inclusions (inside) and blemishes (on the surface). Graders judge it at 10x magnification.\n- GIA's scale has 11 grades in six categories, from Flawless to I3.\n- The grade depends on size, number, position, visibility and darkness, not on a simple count.\n- At least two graders grade independently. They plot the characteristics on a diagram that is a map of that particular stone.\n- Many inclusions that graders find at 10x are not visible to the unaided eye. How visible they are depends on the angle and the light.\n\n**Go further:** in the [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator), step through the clarity grades with **Facet mesh** on. Then you can see which facet each characteristic sits under.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-four-cs/clarity)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Diamond cut grade: Excellent vs Poor, side by side](https://digitalgemology.com/learn/four-cs/diamond-cut-grade-excellent-vs-poor)\n- [Try another topic · Diamond anatomy and proportions: Crown angle and crown height in a round diamond](https://digitalgemology.com/learn/diamond-anatomy/diamond-crown-angle)\n\n[Previous lesson](https://digitalgemology.com/learn/four-cs/fancy-color-diamonds-and-fluorescence) · [The four Cs of diamonds: all lessons](https://digitalgemology.com/learn/four-cs) · [All topics](https://digitalgemology.com/learn)"},{"id":"4C-L6","course":"The four Cs","lesson_number":6,"title":"Diamond cut grade: Excellent vs Poor, side by side","url":"https://digitalgemology.com/learn/four-cs/diamond-cut-grade-excellent-vs-poor","path":"/learn/four-cs/diamond-cut-grade-excellent-vs-poor","markdown":"https://digitalgemology.com/learn/four-cs/diamond-cut-grade-excellent-vs-poor.md","summary":"Diamond cut grade, Excellent vs Poor: what cut means, how a worse cut leaks light (4% vs 45%), and why a Poor 1.00 ct faces up like a 0.86 ct.","queries":["diamond cut grade","excellent cut vs very good cut","why diamond cut matters"],"quiz":"https://digitalgemology.com/skool/quiz/the-four-cs/cut-the-c-you-see","tools":["https://digitalgemology.com/tools/cut-grading-tool","https://digitalgemology.com/tools/3d_gemstone_simulator","https://digitalgemology.com/tools/brightness-tilt-analysis"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[The four Cs of diamonds](https://digitalgemology.com/learn/four-cs) · 4 min read\n\n# Diamond cut grade: Excellent vs Poor, side by side\n\nA diamond cut grade, Excellent to Poor, rates how well the angles and proportions handle light. In our simulator, a 1.00 ct T73 leaks 4% of its face at Excellent and 45% at Poor, and the Poor stone faces up like an Excellent 0.86 ct.\n\nVideo: [The T73 at Excellent and at Poor, turning together](https://www.youtube.com/watch?v=cdz7voAkq-8)\n\nThe T73 at Excellent and at Poor, turning together at their true sizes. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nThe T73 at Excellent and at Poor, turning together at their true sizes.\n\n## Same weight, same color, same clarity\n\nTwo diamonds turn side by side. Both weigh 1.00 carat. Both are D, Flawless. The only difference is the cut: one is Excellent, the other Poor.\n\nThe Excellent stone is a crisp pattern of bright and dark. The Poor one looks flat and washed out across its wide table. And it's smaller: 6.2 mm across against 6.5 mm, but it weighs exactly the same.\n\nColor tints a stone, clarity marks it, carat scales it. Cut is the C that changes the whole face. That's why we call it the C you see.\n\n## Cut is not shape\n\nWhen someone asks for \"an oval cut\", they mean a **shape**: the outline of the stone. The round brilliant is the most common shape. Every other outline (oval, pear, marquise, cushion and the rest) is a **fancy shape**.\n\n**Cut** is something different. It is how well the cutter chose and polished the angles and proportions of the stone, and so how the stone handles light. The beauty of a diamond comes from three things that light does inside it:\n\n- **Brilliance:** the white light it returns to your eye. GIA calls this brightness.\n- **Fire:** the flashes of spectral color as white light splits into its colors.\n- **Scintillation:** the sparkle, and the pattern of bright and dark areas, as the stone, the light or you move.\n\nFine proportions, polish and symmetry make the most of all three.\n\n## Where the light goes\n\nThe key is the **pavilion**, the cone under the girdle. Light goes in through the top. It must bounce off the pavilion facets and come back up through the crown to your eye. If the pavilion is too shallow or too deep, the light hits the facets at the wrong angles. Then it escapes out of the bottom or the side. That's **leakage**.\n\nMore facets won't fix it either. Extra facets cut the reflections into more, smaller pieces, so the pattern of the stone looks busier. But the amount of light that the stone sends back stays the same. The proportions, the polish and the symmetry set that amount.\n\nGIA gives a cut grade, Excellent to Poor, to standard round brilliants only. Fancy shapes are too different for one system, so far.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the [T73](https://digitalgemology.com/cuts/t73-round-brilliant) in diamond. Under **Show**, switch on **Light map**.\n2. In the report, under **Cut grade**, step from **Excellent** through **Very Good**, **Good**, **Fair** to **Poor**. At each step, read the four shares in the report under **Light performance** (Light Return), and the **Measurements**.\n3. **Leak hunt:** at which grade does leakage first go above 10%? And where on the stone does the black show first?\n4. Switch the light map off. Look at the stone itself at Excellent and at Poor, in **Photo studio**.\n5. Open **Proportions** in the report and compare the pavilion angle at Excellent and at Poor.\n\n## What the light map shows\n\n**The light map.** It shows where the light that gets to your eye comes from. The simulator traces it face up, from the geometry only. The colors mean:\n\n- **Red:** direct light from high above (45 to 75 degrees).\n- **Green:** lower, indirect light.\n- **Blue:** contrast, the area that reflects your own head.\n- **Black:** leakage, light that goes out through the pavilion.\n\n| Cut grade | Direct | Indirect | Contrast | Leakage | Diameter |\n| --- | --- | --- | --- | --- | --- |\n| Excellent | 69% | 5% | 22% | 4% | 6.48 mm |\n| Very Good | 57% | 21% | 10% | 13% | 6.44 mm |\n| Good | 54% | 23% | 5% | 18% | 6.38 mm |\n| Fair | 21% | 26% | 24% | 29% | 6.28 mm |\n| Poor | 29% | 8% | 18% | 45% | 6.16 mm |\n\nLeakage goes above 10% at the first step down. At Poor, nearly half the face leaks. Watch *where*. At Good, a dark ring opens around the table. At Poor, the whole outer band of the stone leaks. Only the middle still returns light, and that is why the Poor stone looks bright but flat there.\n\n![The light map face up at Excellent, Good and Poor, at true size.](https://digitalgemology.com/img/learn/4c-l6-t73-light-map-ex-good-poor.webp?v=a0ad34fb)\n\nThe light map face up at Excellent, Good and Poor, at true size.\n\n**What moved.** In the simulator, the cut grade is a fixed schedule that changes the design. At Poor:\n\n- the crown is 2.5° shallower\n- the pavilion is 5.2° steeper (46.0° instead of 40.8°)\n- the girdle is thicker\n- the table and culet are wider.\n\nThat pavilion is the main cause of the leak. The schedule describes the make, the proportions of a cut grade. It isn't GIA's grading, and the shares come from our own render.\n\n**The shrinking diamond.** The weight stays at 1.00 ct. So the extra depth and the thick girdle must come from somewhere: the stone gets narrower. At Poor it's 6.16 mm across, the width of an Excellent T73 of about 0.86 ct. You pay for a carat and see a stone the size of 0.86. A lab grade includes this too: see [how a diamond cut grade is set](https://digitalgemology.com/learn/four-cs/how-diamond-cut-grade-is-determined).\n\n## Key points\n\n- Cut is how well the angles and proportions handle light. Shape is only the outline.\n- A well-cut diamond returns light through the crown. A pavilion that is too shallow or too deep lets light leak out.\n- More facets change the pattern, not how much light comes back.\n- In the simulator, the leakage of the T73 grows from 4% at Excellent to 45% at Poor.\n- At the same weight, a worse cut faces up smaller: a Poor 1.00 ct T73 is as wide as an Excellent 0.86 ct.\n\n**Go further:** the [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis) shows how the brilliance of the T73 changes as you tilt it. The [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool) shows how a lab-style cut grade is put together: see [how a diamond cut grade is set](https://digitalgemology.com/learn/four-cs/how-diamond-cut-grade-is-determined).\n\n## Try it free\n\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n- [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis): Face-up brightness under four standard lights, and how it holds as the stone tilts.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-four-cs/cut-the-c-you-see)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: How a diamond cut grade is set: proportions, polish and symmetry](https://digitalgemology.com/learn/four-cs/how-diamond-cut-grade-is-determined)\n- [Try another topic · The bow-tie effect: Bow-tie in the stone, sometimes on your finger: tilt and head shadow](https://digitalgemology.com/learn/bow-tie/bow-tie-tilt-and-head-shadow)\n\n[Previous lesson](https://digitalgemology.com/learn/four-cs/diamond-clarity-scale) · [The four Cs of diamonds: all lessons](https://digitalgemology.com/learn/four-cs) · [All topics](https://digitalgemology.com/learn)"},{"id":"4C-L7","course":"The four Cs","lesson_number":7,"title":"How a diamond cut grade is set: proportions, polish and symmetry","url":"https://digitalgemology.com/learn/four-cs/how-diamond-cut-grade-is-determined","path":"/learn/four-cs/how-diamond-cut-grade-is-determined","markdown":"https://digitalgemology.com/learn/four-cs/how-diamond-cut-grade-is-determined.md","summary":"How a diamond cut grade is determined: seven components, the weakest sets the grade, and finish caps it. Only 478 of 14,652 combinations are Excellent.","queries":["how is diamond cut grade determined","gia cut grade criteria","excellent cut proportions"],"quiz":"https://digitalgemology.com/skool/quiz/the-four-cs/how-a-cut-grade-is-set","tools":["https://digitalgemology.com/tools/cut-grading-tool"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[The four Cs of diamonds](https://digitalgemology.com/learn/four-cs) · 4 min read\n\n# How a diamond cut grade is set: proportions, polish and symmetry\n\nA diamond cut grade comes from seven components: brilliance, fire, scintillation, weight ratio, durability, polish and symmetry. The system is deductive: the lowest component sets the grade, so Good polish caps a stone with Excellent proportions at Very Good.\n\nVideo: [The T73's pavilion swept across the chart](https://www.youtube.com/watch?v=5f6VEcb3UM4)\n\nThe T73's pavilion swept across the chart, in and out of the Excellent zone. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nThe T73's pavilion swept across the chart, in and out of the Excellent zone.\n\n## 1 in 30\n\nGIA publishes tables to estimate the cut grade of a round brilliant. The tables give every combination of table size, crown angle and pavilion angle, each with its grade. There are 14,652 combinations.\n\nWe counted them. 478 are Excellent. That's about 1 in 30.\n\nMost are Good (45%) or Fair (35%). And the Excellent ones aren't spread out. At a 53% table and a 34.5° crown, the pavilion must be between 40.6° and 41.4°. That window is less than one degree wide. A cutter who misses it by a few tenths of a degree drops a grade.\n\nThis page is about how that grade is put together. It also shows why one small flaw can pull down a stone that is perfect in every other way.\n\n## What goes into a cut grade\n\nGIA's cut grading system for standard round brilliants (D to Z colors, 0.15 ct and larger) went onto its reports in January 2006. GIA built it in two steps:\n\n- First, computer ray tracing of ideal diamonds, to predict how much light and fire they return.\n- Then, more than 70,000 observations of real diamonds by people from the trade and the public. These showed GIA where to put the limits of each grade.\n\nThe grade of a diamond looks at seven components in three groups:\n\n- **Face-up appearance:** brightness, fire and scintillation (in our words: brilliance, fire and scintillation).\n- **Design:** the **weight ratio** and **durability**. The weight ratio tells if the stone has too much weight for its diameter. Durability tells if a very thin girdle puts it at risk.\n- **Craftsmanship:** **polish** and **symmetry**.\n\nAn optical device measures the proportions: table, crown and pavilion angles, star and lower half lengths, girdle thickness and culet. It also measures any painting or digging of the facets. Graders judge polish, symmetry and the girdle and culet descriptions by eye.\n\n## The weakest part wins\n\nHere's the rule that explains everything else: the system is **deductive**. The final grade is the *lowest* grade of the seven components. Six components Excellent and one Good make a Good stone.\n\nEach proportion has its own limits. For Excellent:\n\n- the table can be 52 to 62%\n- the crown angle 31.5° to 36.5°\n- the pavilion 40.6° to 41.8°\n- the total depth 57.5 to 63%.\n\nBut the proportions also work together. Each value can be correct by itself, but the combination can still lower the grade. This happens most when two values are near the edge of their range.\n\nFinish has its own ceiling:\n\n| Polish and symmetry | Best possible cut grade |\n| --- | --- |\n| Excellent or Very Good | Excellent |\n| Good | Very Good |\n| Fair | Good |\n| Poor | Poor |\n\nIn GIA's tests, trained observers saw no clear difference in the face-up look when polish or symmetry was one grade below the other cut components. So Very Good finish still allows an Excellent cut.\n\n### Try it yourself\n\n1. Open [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool). It starts with the [T73](https://digitalgemology.com/cuts/t73-round-brilliant) as cut: 53%, 34.5°, 40.8°. Excellent.\n2. Open **More proportions** and set **Polish** to **Good**. Read the grade and the **Limited by** line.\n3. Put polish back. Set the **Pavilion angle** to 41.6°: by itself, that is inside the Excellent range. What happens? Now also set the **Crown angle** to 31.5°.\n4. **Rescue the Poor stone.** Under **Preset**, choose **Reference stone: Poor**. Bring it to Excellent with as few changes as possible. After each change, read the **Limited by** line: it tells you what holds the stone back now.\n\n## What the Cut Grading Tool shows\n\n**The ceiling.** With Good polish, the grade of the T73 stops at Very Good, but every proportion is still Excellent. The Limited by line tells you that.\n\n**The partnership.** By itself, a 41.6° pavilion is inside the Excellent range. But with this crown and table, the combination is only Very Good. Make the crown shallower, 31.5°, and the pair is Excellent again. A shallower crown and a steeper pavilion balance each other. The grade treats the proportions as a team.\n\n**The rescue.** The Poor reference stone has a 41.0° crown, a 44.0° pavilion, a thick 5.5% girdle, Good polish and Fair symmetry. The tool lists only what holds the stone at its *current* grade. So each fix shows you the next problem:\n\n1. Poor, limited by a total depth of about 72%.\n2. Fix the crown (34.5°) and pavilion (40.8°): **Good**, limited by symmetry Fair.\n3. Raise polish and symmetry to Very Good: **Very Good**, limited by the girdle and the total depth.\n4. Set **Girdle thickness** to 3.0% and **Girdle description** to **Auto** (it reads Medium from the thickness): **Excellent**.\n\nThat's six settings: crown, pavilion, polish, symmetry, girdle thickness and girdle description. The preset sets the girdle description to Thick by itself, so a thinner girdle alone isn't enough. You need each of the six settings. There's no shorter rescue.\n\n**Weight ratio.** Step 3 is the \"shrinking diamond\" of a [Poor cut](https://digitalgemology.com/learn/four-cs/diamond-cut-grade-excellent-vs-poor), in grading terms. A thick girdle and a deep stone carry weight that a viewer can't see face up. The grade counts that against the stone, even when its pattern looks fine.\n\nOur tool reads GIA's published estimation tables for education. It isn't GIA, it's not affiliated with GIA, and its result is not a GIA grade.\n\n## Key points\n\n- GIA's cut grade for round brilliants combines measured proportions with visual checks of polish and symmetry.\n- Seven components count: brilliance, fire, scintillation, weight ratio, durability, polish and symmetry.\n- The grade is deductive: the weakest component sets it.\n- The grade judges the proportions together. Two values that are correct alone can still lower the grade as a pair.\n- Excellent needs polish and symmetry of Very Good or better. In GIA's tables, only about 1 in 30 combinations of table, crown and pavilion is Excellent.\n\n**Go further:** in the [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool), set **Chart view** to **Cut grade**. Open **More proportions** and tick **Show Very Good zone**. Then change the **Table size** and watch the Excellent island move and get smaller.\n\n## Try it free\n\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-four-cs/how-a-cut-grade-is-set)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Putting the 4 Cs together: which C to spend on](https://digitalgemology.com/learn/four-cs/which-of-the-four-cs-matters-most)\n- [Try another topic · Diamond anatomy and proportions: Diamond table percentage: what table size does to the light](https://digitalgemology.com/learn/diamond-anatomy/diamond-table-percentage)\n\n[Previous lesson](https://digitalgemology.com/learn/four-cs/diamond-cut-grade-excellent-vs-poor) · [The four Cs of diamonds: all lessons](https://digitalgemology.com/learn/four-cs) · [All topics](https://digitalgemology.com/learn)"},{"id":"4C-L8","course":"The four Cs","lesson_number":8,"title":"Putting the 4 Cs together: which C to spend on","url":"https://digitalgemology.com/learn/four-cs/which-of-the-four-cs-matters-most","path":"/learn/four-cs/which-of-the-four-cs-matters-most","markdown":"https://digitalgemology.com/learn/four-cs/which-of-the-four-cs-matters-most.md","summary":"Which of the 4 Cs is most important? No single C sets the value, but cut changes the whole face. How to trade color or clarity for size, and when not to.","queries":["which of the 4 cs is most important","how to choose a diamond","best diamond for the money"],"quiz":"https://digitalgemology.com/skool/quiz/the-four-cs/putting-the-four-cs-together","tools":["https://digitalgemology.com/tools/cut-grading-tool","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[The four Cs of diamonds](https://digitalgemology.com/learn/four-cs) · 4 min read\n\n# Putting the 4 Cs together: which C to spend on\n\nNo single C sets the value of a diamond, but cut changes the look most, because it decides how the whole face handles light. A 1.00 ct D Flawless with a Poor cut leaks 45% of its face; an H SI1 with an Excellent cut leaks 4%.\n\n## Which would you wear?\n\nTwo diamonds, both 1.00 carat. The first has the best color and clarity grades there are: **D, Flawless**. The second is an **H, SI1**: four color grades lower, and only one category above the included range.\n\nOn paper, there's no contest. Now look at them.\n\nThe H SI1 is crisp and bright, a sharp pattern of light and dark. The D Flawless looks flat and washed out across its wide table. And it's smaller: 6.2 mm across against 6.5 mm. The D Flawless has a **Poor** cut. The H SI1 has an **Excellent** cut. Under the light map, the D Flawless leaks 45% of its face; the H SI1, 4%.\n\nThe better grades on paper lose. That's the four Cs in one picture.\n\n![D, FL, Poor cut beside H, SI1, Excellent cut, both 1.00 ct, at true size.](https://digitalgemology.com/img/learn/4c-l8-d-fl-poor-vs-h-si1-excellent.webp?v=12971e5e)\n\nD, FL, Poor cut beside H, SI1, Excellent cut, both 1.00 ct, at true size.\n\n## What each C does to the look\n\nHere's what each C changes by itself, with the numbers from our simulator:\n\n- **[Carat](https://digitalgemology.com/learn/four-cs/carat-weight-vs-size)** sets the size, but slowly: double the weight is 26% wider. Round \"magic\" weights cost a step that you can't see: 0.99 ct is 0.02 mm narrower than 1.00 ct.\n- **[Color](https://digitalgemology.com/learn/four-cs/diamond-color-scale-d-to-z)** sets the tint. Near-colorless grades (G to J) look white face up. The tint shows beside a better grade, in larger stones and lower on the scale. Warm light can hide four letters.\n- **[Clarity](https://digitalgemology.com/learn/four-cs/diamond-clarity-scale)** sets what a grader finds at 10x. In SI stones, graders find many inclusions only under magnification. And visibility changes with the angle and the light.\n- **[Cut](https://digitalgemology.com/learn/four-cs/diamond-cut-grade-excellent-vs-poor)** sets how the whole face handles light, and even how big a carat looks. A Poor 1.00 ct [T73](https://digitalgemology.com/cuts/t73-round-brilliant) faces up like an Excellent 0.86 ct.\n\nNo single C sets the value of a diamond. All four do, together. But they don't change the *look* equally. Color and clarity mostly matter where you can see them. Cut changes every square millimeter.\n\n## Trading one C for another\n\nReal buying is about trade-offs. Here is a common one, straight from the advice of jewelers: to go up in size, go slightly lower on color, clarity or cut. Larger diamonds are rarer, so the price goes up faster than the weight. A step down in another C can pay for the step up in carat.\n\nThat's a fair trade for color and clarity, if you stay where the eye can't see the difference. Cut is different. It's the C you see, so a step down in cut costs you looks directly.\n\nAnd remember: a cut grade points you to the looks that most people like, but light changes everything. GIA's own advice is to look at a diamond in several kinds of light, and then to choose the one that pleases your eye.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the T73 in diamond, **Photo studio**.\n2. **Stone A, bigger:** 1.50 ct, color **K**, clarity **SI2**, cut **Good**. Write down the measurements and take a screenshot.\n3. **Stone B, better cut:** 1.00 ct, color **G**, clarity **VS2**, cut **Excellent**. Write down the measurements and take a screenshot.\n4. Look at both in **Home** light too, and with the **Light map** on.\n5. **Make the decision:** which one do you buy, and why? Then build your own pair with the same logic and test it.\n\n## What the simulator shows\n\n**Stone A** is clearly bigger: 7.3 mm against 6.5 mm, about 27% more face. It shows a faint warmth. Its Good cut leaks 18% of the face, against 4% for Stone B. **Stone B** is smaller, whiter and crisper.\n\n![The two stones at true size, in the photo studio and under warm home light.](https://digitalgemology.com/img/learn/4c-l8-bigger-vs-better-cut.webp?v=2f15c6b4) ![The two stones at true size, in the photo studio and under warm home light.](https://digitalgemology.com/img/learn/4c-l8-bigger-vs-better-cut-home.webp?v=800aa3fc)\n\nThe two stones at true size, in the photo studio and under warm home light.\n\nThere's no wrong answer here, and that's the point. Some people want the size and don't mind the warmth. Others want the sparkle. Under warm home light, the color difference gets smaller, because the light is warm anyway. With the light map on, the cut difference stays the same. The four Cs give you a shared language to describe the choice. Your eyes make it.\n\n## Key points\n\n- No single C sets the value of a diamond. All four do, together.\n- They don't change the look equally. Cut changes the whole face. Color and clarity matter where you can see them.\n- A stone with top color and clarity grades can look worse than a stone with lower grades and a better cut.\n- It is common and fair to trade color or clarity for size, if you stay below what the eye can see. A trade that gives away cut costs looks directly.\n- Look at any diamond in several kinds of light before you decide.\n\n**Go further:** [take the four Cs quiz](https://digitalgemology.com/skool/quiz/the-four-cs) to check all four Cs at once.\n\n## Try it free\n\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-four-cs/putting-the-four-cs-together)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Try another topic · Diamond anatomy and proportions: The parts of a diamond: crown, girdle and pavilion](https://digitalgemology.com/learn/diamond-anatomy/parts-of-a-diamond)\n\n[Previous lesson](https://digitalgemology.com/learn/four-cs/how-diamond-cut-grade-is-determined) · [The four Cs of diamonds: all lessons](https://digitalgemology.com/learn/four-cs) · [All topics](https://digitalgemology.com/learn)"},{"id":"AOD-L1","course":"Anatomy of a diamond","lesson_number":1,"title":"The parts of a diamond: crown, girdle and pavilion","url":"https://digitalgemology.com/learn/diamond-anatomy/parts-of-a-diamond","path":"/learn/diamond-anatomy/parts-of-a-diamond","markdown":"https://digitalgemology.com/learn/diamond-anatomy/parts-of-a-diamond.md","summary":"The parts of a diamond: the crown, girdle and pavilion, the 57 facets of a round brilliant by name, and what each part does with light.","queries":["parts of a diamond","diamond anatomy","diamond facets names"],"quiz":"https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/three-parts-of-a-diamond","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator","https://digitalgemology.com/tools/cut-grading-tool"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant","https://digitalgemology.com/cuts/t57-round-brilliant"],"text":"[Diamond anatomy and proportions](https://digitalgemology.com/learn/diamond-anatomy) · 4 min read\n\n# The parts of a diamond: crown, girdle and pavilion\n\nA diamond has three parts: the crown on top, the girdle at the widest point and the pavilion below. A standard round brilliant has 33 facets on the crown and 24 on the pavilion: 57 in all, or 58 with a culet facet.\n\nVideo: [The T73 turning, seen from 60°, with every facet edge drawn](https://www.youtube.com/watch?v=XY6EXlrCHf4)\n\nThe T73 turning, seen from 60°, with every facet edge drawn. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nThe T73 turning, seen from 60°, with every facet edge drawn.\n\n## Turn the stone sideways\n\nCut decides how a diamond looks. To talk about cut, we need names for the parts.\n\nFace-up, a round diamond is a busy pattern of bright and dark slivers. Turn it on its side and it gets simple. You see a low roof on top, a thin edge at the widest point, and a deep cone below. Every cut term that we use belongs to one of those three parts.\n\n## Crown, girdle, pavilion\n\n**The crown** is all of the diamond above the widest point. A standard round brilliant has 33 facets here:\n\n- the **table**, the large flat octagon on top;\n- 8 **star facets**, small triangles that touch the table;\n- 8 **bezel facets**, the large four-sided facets that go from the table to the edge;\n- 16 **upper half facets**, small triangles along the edge, two between each pair of bezels.\n\n**The girdle** is the narrow band at the widest point. It is the edge that a setting grips. The cutter can leave it rough from shaping (bruted), polish it, or cut it into its own row of small facets.\n\n**The pavilion** is the cone below the girdle. It has 24 facets:\n\n- 8 **pavilion mains**, long facets that go from the girdle to the point;\n- 16 **lower half facets**, long thin triangles along the girdle, two between each pair of mains.\n\nThe point at the bottom is the **culet**. Sometimes the cutter polishes it into a tiny flat facet, parallel to the table, to protect the tip. If not, the mains simply meet in a point.\n\nSo the count is 33 + 24 = 57 facets, or 58 with a culet facet. We count the girdle facets separately.\n\n![The T73 side on, edges drawn: the crown on top, the girdle band at the widest point, the pavilion below.](https://digitalgemology.com/img/learn/aod-l1-t73-profile-mesh.webp?v=3947290e)\n\nThe T73 side on, edges drawn: the crown on top, the girdle band at the widest point, the pavilion below.\n\n![The T57's crown seen from above and its pavilion seen from below, each facet type in its own shade and named: table, stars, bezels, upper halves; pavilion mains, lower halves.](https://digitalgemology.com/img/learn/aod-l1-t57-facet-types-plans.webp?v=66c43c25)\n\nThe T57's crown seen from above and its pavilion seen from below, each facet type in its own shade and named: table, stars, bezels, upper halves; pavilion mains, lower halves.\n\n## What each part does with light\n\nLight enters through the crown, mostly through the table, and goes down to the pavilion. The pavilion facets work like mirrors. Light that hits them at a steep enough slant bounces back up. (This is simplified. Our page on the [pavilion angle](https://digitalgemology.com/learn/diamond-anatomy/diamond-pavilion-angle) shows when the mirror fails.)\n\nOn the way out, the sloped crown facets bend the light. Each color bends by a slightly different amount. That spreads white light into flashes of color: fire.\n\nThe girdle and the culet have no optical job. They protect the edge and the point.\n\n### Try it yourself\n\n1. Open [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool). It starts on the [T73 Round Brilliant](https://digitalgemology.com/cuts/t73-round-brilliant) as cut.\n2. In the **Crown plan**, find the table. Then count the stars, the bezels and the upper halves.\n3. Switch to **Profile** and find the band where the crown meets the pavilion: the girdle.\n4. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) and load the **[T57 Round Brilliant](https://digitalgemology.com/cuts/t57-round-brilliant)**. Turn on **Facet mesh** and turn the stone over. Count the pavilion mains.\n5. Load the **T73 Round Brilliant** and look at the edge. What changed?\n\n![What the Cut Grading Tool shows for the T73 as cut: 3D view, crown plan, profile and light map, graded Excellent.](https://digitalgemology.com/img/learn/aod-l1-t73-cgt-views.webp?v=2a4574e7)\n\nWhat the Cut Grading Tool shows for the T73 as cut: 3D view, crown plan, profile and light map, graded Excellent.\n\n## What the T57 and the T73 show\n\nThe T57 and the T73 have the same 57 facets at the same angles. The T57 has a knife-edge: the crown and the pavilion meet in a sharp line, with no girdle. The T73 adds a girdle band of 16 small facets. Most round brilliants get this finish today.\n\n![The T73 drawn the same way as the T57 above, with a side view between the plans: its 16 girdle facets stand upright, so only the side view shows them.](https://digitalgemology.com/img/learn/aod-l1-t73-facet-types-plans.webp?v=764a6b73)\n\nThe T73 drawn the same way as the T57 above, with a side view between the plans: its 16 girdle facets stand upright, so only the side view shows them.\n\nThat thin band is important. At the same width, the T73 is 61.7% deep and weighs 1.99 ct. The T57 is 59.2% deep and weighs 1.81 ct. Our page on [girdle thickness](https://digitalgemology.com/learn/diamond-anatomy/diamond-girdle-thickness) tells you more.\n\n![The same thing turned around: both stones at 1.00 ct, face up with edges drawn, at true size. The crown patterns match, but the knife-edged T57 is 6.7 mm across and the T73 6.5 mm.](https://digitalgemology.com/img/learn/aod-l1-t57-vs-t73-face-up-mesh.webp?v=7ffa006a)\n\nThe same thing turned around: both stones at 1.00 ct, face up with edges drawn, at true size. The crown patterns match, but the knife-edged T57 is 6.7 mm across and the T73 6.5 mm.\n\n## Key points\n\n- A round brilliant has a crown on top, a girdle at the widest point and a pavilion below.\n- The crown has 33 facets and the pavilion has 24: 57 in all, or 58 when the point is polished into a culet.\n- Light enters and leaves through the crown. The pavilion reflects it back up, and the sloped crown facets spread it into color.\n- The girdle and the culet give protection. They do nothing for light.\n\n**Go further:** see the [T57](https://digitalgemology.com/cuts/t57-round-brilliant) and [T73](https://digitalgemology.com/cuts/t73-round-brilliant) cut pages, face-up and in profile.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/three-parts-of-a-diamond)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n- [T57 Round Brilliant Cut](https://digitalgemology.com/cuts/t57-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Diamond measurements explained: diameter, depth and percentages](https://digitalgemology.com/learn/diamond-anatomy/diamond-measurements-explained)\n- [Try another topic · Historic diamond cuts: the history of the brilliant: Tolkowsky's 1919 ideal cut: the brilliant that was calculated](https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919)\n\n[Diamond anatomy and proportions: all lessons](https://digitalgemology.com/learn/diamond-anatomy) · [All topics](https://digitalgemology.com/learn)"},{"id":"AOD-L2","course":"Anatomy of a diamond","lesson_number":2,"title":"Diamond measurements explained: diameter, depth and percentages","url":"https://digitalgemology.com/learn/diamond-anatomy/diamond-measurements-explained","path":"/learn/diamond-anatomy/diamond-measurements-explained","markdown":"https://digitalgemology.com/learn/diamond-anatomy/diamond-measurements-explained.md","summary":"Diamond measurements explained: read min – max × depth in mm, turn it into a depth percentage, and see how crown, girdle and pavilion add up.","queries":["diamond measurements","diamond depth percentage","diamond mm measurements"],"quiz":"https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/how-a-diamond-is-measured","tools":["https://digitalgemology.com/tools/cut-grading-tool","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Diamond anatomy and proportions](https://digitalgemology.com/learn/diamond-anatomy) · 4 min read\n\n# Diamond measurements explained: diameter, depth and percentages\n\nA round diamond's measurements read minimum diameter – maximum diameter × depth, in millimeters. Every other proportion is an angle or a percentage of the average diameter, and the total depth is the crown height + the girdle + the pavilion depth.\n\n## Two lines, one secret\n\nTwo grading reports, both for a 1.00 ct round diamond. The measurements read:\n\n- Stone 1: **6.48 – 6.48 × 4.00 mm**\n- Stone 2: **6.16 – 6.16 × 4.16 mm**\n\nYou cannot see either stone. Which one faces up bigger, and which one hides weight where you can't see it?\n\nDivide the depth by the diameter. Stone 1 is 61.7% deep. Stone 2 is about 67.5% deep. (The simulator's report uses unrounded figures and says 67.6%.) That stone is narrower and taller, so the same carat sits lower down, out of sight. Those two lines are the [T73](https://digitalgemology.com/cuts/t73-round-brilliant) in our simulator at Excellent and at Poor cut. This page shows you how to read a report the same way.\n\n![The two 1.00 ct stones side on, at true size.](https://digitalgemology.com/img/learn/aod-l2-t73-excellent-vs-poor-profile.webp?v=b3cc8382)\n\nThe two 1.00 ct stones side on, at true size.\n\n## Everything is a share of the diameter\n\nOn a report, the size of a round diamond is written as **minimum diameter – maximum diameter × depth**, in millimeters. (Fancy shapes give length × width × depth.) No round is perfectly round. So the lab measures the narrowest and the widest diameter across the girdle. Their average is the yardstick for all the other numbers. A big gap between the two shows that the stone is out of round.\n\nEvery other proportion is an **angle**, in degrees, or a **percentage of that average diameter**:\n\n- **table size:** the width of the table;\n- **crown height:** from the girdle to the table;\n- **girdle thickness;**\n- **pavilion depth:** from the girdle to the culet;\n- **total depth:** from the table to the culet;\n- **culet size.**\n\nWith percentages, you can compare stones of any size: a 0.5 ct and a 5 ct with the same proportions read the same numbers. The habit is old. In 1919, Tolkowsky calculated his ideal round. He set the diameter at 100 units. He gave the table as 53.0, the part above the girdle as 16.2 and the part below as 43.1.\n\nThe lab measures all this with an optical device that never touches the stone. The report draws the result as a **proportion diagram**: the profile of the stone, with its numbers.\n\n## Three heights make the depth\n\nLook at a diamond side on. The total depth has three stacked parts:\n\n**crown height + girdle + pavilion depth = total depth**\n\nTwo of those parts come from the angles. The crown height depends on the crown angle and on the width of the crown's ring (the table takes the rest). The pavilion depth depends on the pavilion angle only.\n\nHere are the numbers in our Cut Grading Tool:\n\n- The T73's 53% table and 34.5° crown give a crown height of 16.2%.\n- Its 40.8° pavilion gives a pavilion depth of 43.2%.\n- With its 2.5% girdle, the tool calculates a total depth of 61.6%.\n\n![The T73 side on, its crown height, girdle and pavilion depth stacked into the total depth.](https://digitalgemology.com/img/learn/aod-l2-diagram-depth.webp?v=d169d2c0)\n\nThe T73 side on, its crown height, girdle and pavilion depth stacked into the total depth.\n\nTwo small details explain why the sums are never exact. The tool's profile rounds the crown height and the pavilion depth to the nearest half percent. Also, its depth formula subtracts a small calibration (0.25%). We measured the T73's own 3D model directly: it is 61.7% deep.\n\nThe girdle is the one height with no angle. That makes it a quiet way to add depth, and weight.\n\n### Try it yourself\n\n1. Open [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool). It starts on the T73 as cut. Look at the **Profile** view. Read the crown height, the girdle, the pavilion depth and the total depth.\n2. Open **More proportions** and raise **Girdle thickness** from 2.5% to 7.5%. Which numbers in the profile move, and which stay the same? Watch the grade.\n3. Put the girdle back and change the **Crown angle**. Which numbers move now?\n4. **Report detective.** Calculate the total depth of these three made-up 1.00 ct rounds. Which one do you look at first?\n  - A: 6.48 – 6.52 × 4.00 mm\n  - B: 6.20 – 6.22 × 4.18 mm\n  - C: 6.40 – 6.60 × 3.95 mm\n\n## What the Cut Grading Tool shows\n\n**The girdle moves only the total.** From 2.5% to 7.5%, the crown height (about 16.0%) and the pavilion depth (about 43.0%) do not change. But the total depth climbs from 61.6% to 66.6%, and the grade falls from Excellent to Fair. The tool tells you why. The total depth is past even the Good limit (66.5%), so the stone has a lot of extra weight for its diameter.\n\n**The crown angle moves the crown height.** A steeper crown gives a taller crown, and the total depth follows. The pavilion does not change.\n\n**Report detective.** A is 6.50 mm on average and 61.5% deep. B is 6.21 mm and 67.3% deep: narrow and deep, so B hides weight. C is 6.50 mm and 60.8% deep, but look at the diameters: 6.40 against 6.60, a 0.20 mm gap. C is out of round, and that gap needs a closer look.\n\n## Key points\n\n- The measurements of a round diamond read minimum diameter – maximum diameter × depth. The average diameter is the yardstick.\n- Every proportion is an angle or a percentage of the average diameter, so you can compare stones of any size.\n- Total depth is crown height plus girdle plus pavilion depth.\n- The angles set the crown height and the pavilion depth. The girdle adds depth with no angle at all.\n- Divide the depth by the diameter. From the paperwork alone, this tells you if a stone has extra weight below its face.\n\n**Go further:** the [T73 cut page](https://digitalgemology.com/cuts/t73-round-brilliant) gives the model's own measurements: 8.15 × 8.15 × 5.03 mm, 61.7% deep.\n\n## Try it free\n\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/how-a-diamond-is-measured)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Diamond table percentage: what table size does to the light](https://digitalgemology.com/learn/diamond-anatomy/diamond-table-percentage)\n- [Try another topic · How to read a diamond grading report: How to read the proportion diagram on a diamond report](https://digitalgemology.com/learn/grading-reports/diamond-proportion-diagram)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-anatomy/parts-of-a-diamond) · [Diamond anatomy and proportions: all lessons](https://digitalgemology.com/learn/diamond-anatomy) · [All topics](https://digitalgemology.com/learn)"},{"id":"AOD-L3","course":"Anatomy of a diamond","lesson_number":3,"title":"Diamond table percentage: what table size does to the light","url":"https://digitalgemology.com/learn/diamond-anatomy/diamond-table-percentage","path":"/learn/diamond-anatomy/diamond-table-percentage","markdown":"https://digitalgemology.com/learn/diamond-anatomy/diamond-table-percentage.md","summary":"Diamond table percentage: how table size is measured, GIA's 52 to 62% Excellent range, and why a bigger table is not automatically brighter.","queries":["diamond table percentage","ideal table size round diamond","table and depth diamond"],"quiz":"https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/table-size","tools":["https://digitalgemology.com/tools/cut-grading-tool"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Diamond anatomy and proportions](https://digitalgemology.com/learn/diamond-anatomy) · 3 min read\n\n# Diamond table percentage: what table size does to the light\n\nTable percentage is the width of the table as a share of the diameter. GIA's Excellent limit for the table alone is 52 to 62%, but bigger is not automatically brighter: at the T73's angles, our traced brilliance peaks at a 53 to 55% table.\n\nVideo: [The table from 52% to 62% and back with the angles fixed](https://www.youtube.com/watch?v=8ThEno1TCgw)\n\nThe table from 52% to 62% and back with the angles fixed. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nThe table from 52% to 62% and back with the angles fixed.\n\n## The shrinking island\n\nGIA publishes a chart of grades for every combination of crown angle and pavilion angle. There is one chart for each table size. On most charts, the Excellent combinations make a small island in a sea of lower grades.\n\nAt a 53% table, the island has 45 cells. At 55 and 56%, it's at its biggest: 57 cells. Then it shrinks: 40 at 60%, 26 at 61%, 16 at 62%. At 63% it's gone. Not one combination of crown and pavilion makes a 63% table Excellent.\n\nSo the table, the biggest facet on the stone, quietly sets how much room every other proportion has. Let's see why.\n\n## Measuring the window\n\nThe **table** is the flat octagon on top: the window where most light enters. Its size is a percentage of the diameter. Our Cut Grading Tool measures it corner to corner, from one point of the octagon to the opposite one.\n\nFor an Excellent grade, GIA's limits put the table on its own between 52% and 62%. But the table never works alone. The crown is a ring around it, and the slope of the ring is the crown angle. Make the table bigger at the same crown angle, and the ring gets narrower. So the crown gets lower: the crown height drops. A lower crown changes how the crown facets catch light on the way out.\n\n## Bigger is not automatically brighter\n\nIt sounds logical: a bigger window lets in more light. But the brilliance of a diamond is not the light that goes *in*. It is the light that comes back *out* to your eye, and that depends on the full path.\n\nOur Cut Grading Tool traces brilliance for every cell of every table. It measures the light that the stone returns as it tilts 30° each way under an evenly lit dome. Your head blocks the light from above. At the [T73](https://digitalgemology.com/cuts/t73-round-brilliant)'s angles, the brilliance peaks at a 53 to 55% table, 54.2%. It falls slowly as the table grows: 52.2% at 62%. A bigger table changes the pattern and the crown, not only the window.\n\nGIA's own examples show the other side. On a stone with a shallow crown, a wider table can make the stone look livelier, but its pattern changes. It depends on the combination.\n\n### Try it yourself\n\n1. Open [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool). It starts on the T73: 53% table, 34.5° crown, 40.8° pavilion.\n2. Raise the **Table size** one step at a time to 63%. At each step, read the crown height and the total depth in the **Profile**, and read the grade.\n3. Set **Chart view** to **Cut grade** and watch the Excellent island as you change the table. Then set it to **Brilliance**.\n4. **The challenge:** set the table to 62%. The T73's angles only make Very Good here. Find a crown and a pavilion that make a 62% table Excellent.\n\n## What the Cut Grading Tool shows\n\n**The profile.** From 52% to 63%, the crown height falls from about 16.5% to 12.5%. The total depth falls from 61.9% to 58.1%. The angles never moved: the bigger table simply leaves a narrower crown ring.\n\n**The grade.** At the T73's angles, every table from 52% to 61% is Excellent. At 62% it drops to Very Good: the tool says that the combination of crown and pavilion doesn't work at that table. At 63% the table itself is past the limit.\n\n**The challenge.** A 62% table is Excellent with crowns from 33.0° to 35.0° and pavilions from 41.0° to 41.6°, in 16 combinations. One answer: keep the 34.5° crown and make the pavilion steeper, at 41.0°.\n\nOne honest note: the tool traces its light map on the T73 at a 53% table, so the light map doesn't change with the table. Use the Brilliance chart for that.\n\n## Key points\n\n- The table is measured as a percentage of the diameter. Our tool measures it corner to corner.\n- GIA's Excellent limit for the table alone is 52 to 62%, but the table, crown and pavilion are graded together.\n- At the same crown angle, a bigger table gives a lower crown and a shallower stone.\n- A bigger table is not automatically brighter. In our traced brilliance at the T73's angles, it peaks at 53 to 55% and then falls slowly.\n- The Excellent island is biggest at 55 to 56% tables and disappears above 62%.\n\n**Go further:** read about the [crown angle and crown height](https://digitalgemology.com/learn/diamond-anatomy/diamond-crown-angle), and the 1919 calculation behind the T73's 34.5°.\n\n## Try it free\n\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/table-size)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Crown angle and crown height in a round diamond](https://digitalgemology.com/learn/diamond-anatomy/diamond-crown-angle)\n- [Try another topic · The four Cs of diamonds: Diamond cut grade: Excellent vs Poor, side by side](https://digitalgemology.com/learn/four-cs/diamond-cut-grade-excellent-vs-poor)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-anatomy/diamond-measurements-explained) · [Diamond anatomy and proportions: all lessons](https://digitalgemology.com/learn/diamond-anatomy) · [All topics](https://digitalgemology.com/learn)"},{"id":"AOD-L4","course":"Anatomy of a diamond","lesson_number":4,"title":"Crown angle and crown height in a round diamond","url":"https://digitalgemology.com/learn/diamond-anatomy/diamond-crown-angle","path":"/learn/diamond-anatomy/diamond-crown-angle","markdown":"https://digitalgemology.com/learn/diamond-anatomy/diamond-crown-angle.md","summary":"Diamond crown angle: what the crown does with light, GIA's 31.5° to 36.5° Excellent range, how it sets crown height, and Tolkowsky's 34.5°.","queries":["diamond crown angle","ideal crown angle","crown height percentage"],"quiz":"https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/crown-angle-and-crown-height","tools":["https://digitalgemology.com/tools/cut-grading-tool"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant","https://digitalgemology.com/cuts/t57-round-brilliant"],"text":"[Diamond anatomy and proportions](https://digitalgemology.com/learn/diamond-anatomy) · 3 min read\n\n# Crown angle and crown height in a round diamond\n\nThe crown angle is the slope of the bezel facets against the girdle plane, and Tolkowsky calculated 34.5° for it in 1919. GIA's Excellent limits are 31.5° to 36.5° for the crown angle and 12.5% to 17.0% for the crown height, each on its own.\n\nVideo: [The crown angle swept from 31.5° to 37.5° and back](https://www.youtube.com/watch?v=VuH2XanRv3g)\n\nThe crown angle swept from 31.5° to 37.5° and back. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nThe crown angle swept from 31.5° to 37.5° and back.\n\n## 34.5° from 1919\n\nIn 1919, Marcel Tolkowsky published a short book. In it, he calculated the paths of light through a diamond and found the best angles for a round brilliant. For the crown he got 34°30': 34.5°.\n\nMore than a century later, our [T73](https://digitalgemology.com/cuts/t73-round-brilliant) is cut to his angles. Our Cut Grading Tool reads GIA's published tables and grades it Excellent. Tilt that crown, and the T73 stays Excellent from 33.5° all the way to 36.0°: a window two and a half degrees wide. That's generous. For the [pavilion angle](https://digitalgemology.com/learn/diamond-anatomy/diamond-pavilion-angle), the same window is less than one degree.\n\nSo why does the crown get more room, and what does it do up there?\n\n## What the crown angle is\n\nThe **crown angle** is the slope of the bezel facets, the big four-sided facets of the crown. It is measured against the flat plane of the girdle. A low angle gives a flat, low crown. A high angle gives a steep, tall crown.\n\nThe crown meets light twice. On the way in, it lets light through the table and the crown facets. On the way out, the pavilion sends light back up, and that light crosses the crown again. The sloped crown facets bend it. Each color bends by a slightly different amount, so white light fans out into flashes of color: fire.\n\n## Crown height: angle plus table\n\nThe **crown height**, from the girdle to the table, comes from two numbers. The crown is a ring around the table, and the angle is the slope of that ring:\n\n**crown height = half of (100% − table) × the tangent of the crown angle**\n\nFor the T73, half of 47% is 23.5%. At 34.5°, that ring rises to about 16% of the diameter. Make the crown steeper and the height grows. Make the [table wider](https://digitalgemology.com/learn/diamond-anatomy/diamond-table-percentage) and the height shrinks.\n\nGIA's limits for an Excellent grade, each on its own: a crown angle from 31.5° to 36.5°, and a crown height from 12.5% to 17.0%. A stone can fail on either one.\n\n### Try it yourself\n\n1. Open [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool). It starts on the T73: 53% table, 34.5° crown, 40.8° pavilion.\n2. Move the **Crown angle** down to 30.5° and up to 38.0°, half a degree at a time. Read the crown height in the **Profile**. Read the grade and its **Limited by** line.\n3. Set **Chart view** to **Fire**, then to **Brilliance**. Watch where the T73's marker sits as you move the crown.\n4. **The rescue.** Set the crown to 31.5°: Very Good. Do not touch the crown. Find the pavilion angles that make it Excellent again.\n\n## What the Cut Grading Tool shows\n\n**The window.** At the T73's table and pavilion, the grade is Excellent from 33.5° to 36.0°. Below that, the combination of crown and pavilion fails (31.5 to 33.0°). Below 31.5°, the crown angle itself is out of range. Above the window, the crown height fails first. At 36.5° it reaches about 17.5%, past the 17.0% limit. At 38.0° it is about 18.5%, and the stone is only Good. Across the sweep, the crown height climbs from about 14% to 18.5%.\n\n**Brilliance and fire.** In the tool's traced brilliance, a steeper crown returns a little more light at these settings. It reads 50.3% at 31.5°, 54.2% at 34.5° and 56.1% at 36.0°. The Fire chart is a model, not a trace. It peaks at about a 35.5° crown and a 40.9° pavilion, close to Tolkowsky's angles. GIA's examples add the look: stones with flat crowns tend to look darker overall.\n\n**The rescue.** A 31.5° crown is Excellent with a pavilion from 41.2° to 41.8°. A flatter crown and a steeper pavilion balance each other: the light that the pavilion sends up meets a crown with a different slope. The crown and the pavilion are graded as a pair, never alone.\n\n## Key points\n\n- The crown angle is the slope of the bezel facets against the girdle plane. The T73's 34.5° comes from Tolkowsky's 1919 calculation.\n- The crown bends light on its way out, and this spreads the light into fire.\n- The crown height comes from the table and the crown angle: half of (100% − table) × tan(crown angle).\n- GIA's Excellent limits: crown angle 31.5° to 36.5° and crown height 12.5% to 17.0%, each on its own.\n- A steeper pavilion can balance a shallow crown: at a 53% table, 31.5° works with 41.2° to 41.8°.\n\n**Go further:** the [T57 Round Brilliant cut page](https://digitalgemology.com/cuts/t57-round-brilliant) has Tolkowsky's round as he published it, with its knife-edge.\n\n## Try it free\n\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/crown-angle-and-crown-height)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n- [T57 Round Brilliant Cut](https://digitalgemology.com/cuts/t57-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Pavilion angle and pavilion depth: how a diamond keeps the light in](https://digitalgemology.com/learn/diamond-anatomy/diamond-pavilion-angle)\n- [Try another topic · Historic diamond cuts: the history of the brilliant: Hearts and arrows diamonds: precision you can see](https://digitalgemology.com/learn/historic-cuts/hearts-and-arrows-diamonds)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-anatomy/diamond-table-percentage) · [Diamond anatomy and proportions: all lessons](https://digitalgemology.com/learn/diamond-anatomy) · [All topics](https://digitalgemology.com/learn)"},{"id":"AOD-L5","course":"Anatomy of a diamond","lesson_number":5,"title":"Pavilion angle and pavilion depth: how a diamond keeps the light in","url":"https://digitalgemology.com/learn/diamond-anatomy/diamond-pavilion-angle","path":"/learn/diamond-anatomy/diamond-pavilion-angle","markdown":"https://digitalgemology.com/learn/diamond-anatomy/diamond-pavilion-angle.md","summary":"Pavilion angle explained: how the pavilion reflects light past the 24.4° critical angle, sets the pavilion depth, and why Excellent is so narrow.","queries":["pavilion angle","ideal pavilion angle","pavilion depth diamond"],"quiz":"https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/pavilion-angle-and-pavilion-depth","tools":["https://digitalgemology.com/tools/cut-grading-tool"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant","https://digitalgemology.com/cuts/t57-round-brilliant"],"text":"[Diamond anatomy and proportions](https://digitalgemology.com/learn/diamond-anatomy) · 4 min read\n\n# Pavilion angle and pavilion depth: how a diamond keeps the light in\n\nThe pavilion angle is the slope of the pavilion mains against the girdle plane. It sets the pavilion depth and how much light the pavilion reflects back up; on our T73 round brilliant, the grade stays Excellent only from 40.6° to 41.4°.\n\nVideo: [Pavilion angle explained: how a diamond keeps the light in (animated)](https://www.youtube.com/watch?v=V8y_B41j3XI)\n\nOne pavilion facet, close up. Past the 24.4° critical angle, the facet reflects all the light: total internal reflection. Then the T73's two-bounce path, and the Cut Grading Tool's light maps at 39.4°, 40.8° and 42.4°. The Excellent window runs from 40.6° to 41.4°. · 1 min 30 s · No sound, captions on screen\n\n## Transcript\n\nThe pavilion angle is the slope of the lower facets.\n\nThis is one pavilion facet, close up. The dashed line is square to the facet.\n\nClose to square-on, most of the light goes out through the facet.\n\nTilt the light. At 24.4°, the critical angle, the light can no longer get out.\n\nPast the critical angle, the facet reflects all the light: total internal reflection.\n\nLight goes in through the top. It meets the pavilion at 40.8°.\n\nThat is more than 24.4°, so the facet reflects all of it.\n\nIt meets the other side at 57.6° and reflects again.\n\nThen it goes out through the top, back to you. The pavilion works as a mirror.\n\nA real diamond gets light from all sides. The Cut Grading Tool traces it in 3D.\n\nRed: light from above. Green: low light. Blue: your own head. Black: light lost.\n\nThe T73 at 40.8°: 69% direct light, and 22% contrast for the pattern.\n\nToo shallow: blue grows to 36%. The stone shows you more of your own head.\n\nToo steep: green grows to 30%, and 9% of the light goes out through the back.\n\nBack to the T73 at 40.8°.\n\nExcellent runs from 40.6° to 41.4° at this table and crown. The window is 0.8° wide.\n\n## Two tenths of a degree\n\nTake the [T73](https://digitalgemology.com/cuts/t73-round-brilliant) in our Cut Grading Tool and change one number: the pavilion angle, from 40.6° to 40.4°. Two tenths of a degree. Nobody could see that on a stone. The grade drops from Excellent to Very Good.\n\nNow go the other way. At the T73's table and crown, the pavilion is Excellent from 40.6° to 41.4°, a window only 0.8° wide. The [crown angle](https://digitalgemology.com/learn/diamond-anatomy/diamond-crown-angle) has a window of two and a half degrees.\n\nAnd here's the twist: at 42.4°, far outside that window, the tool's traced brilliance is the highest of the whole sweep. It reads 62.6%, against 54.2% at the T73's 40.8°. The brightest pavilion grades only Good. This page shows why. You'll also see that Tolkowsky refused the steeper pavilion too, in 1919, for a reason of his own: fire.\n\nVideo: [The pavilion swept from 39.8° to 41.8° and back](https://www.youtube.com/watch?v=E7Gr2cemgHA)\n\nThe pavilion swept from 39.8° to 41.8° and back, the light map changing. · 10 s · No sound\n\n## The pavilion is a mirror\n\nThe **pavilion angle** is the slope of the pavilion mains against the girdle plane. With the diameter, only this angle sets the **pavilion depth**: half the diameter × the tangent of the angle. At 40.8° that's about 43% of the diameter.\n\nIn [the parts of a diamond](https://digitalgemology.com/learn/diamond-anatomy/parts-of-a-diamond) we said that the pavilion works like a mirror. Here's when it does. Inside a diamond, light that meets a facet at a slant, far enough from square-on, can't get out: it reflects completely. The limit is the **critical angle**, 24.4° from the facet's perpendicular in diamond. At more of a slant than that, light reflects completely. Closer to square-on, most of it escapes out of the back. A well-cut pavilion catches the light at slants that keep it bouncing until it reaches the crown.\n\nChange the pavilion angle and you change every slant at the same time. Is the pavilion too shallow or too deep? Then more of the light meets a facet that it can escape through, out of the bottom or the side.\n\n## What the light map shows\n\nThe tool's light map shows where the light that reaches your eye comes from:\n\n- **red** for direct light from high above;\n- **green** for lower, indirect light;\n- **blue** for contrast (the reflection of your own head);\n- **black** for leakage.\n\n![The light map classes by the elevation the light comes from: contrast at 75° and above, direct from 45° to 75°, indirect below 45°.](https://digitalgemology.com/img/learn/aod-l5-diagram-light-zones.webp?v=680b7f92)\n\nThe light map classes by the elevation the light comes from: contrast at 75° and above, direct from 45° to 75°, indirect below 45°.\n\n### Try it yourself\n\n1. Open [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool). It starts on the T73: 53% table, 34.5° crown, 40.8° pavilion.\n2. Move the **Pavilion angle** down to 39.4° and up to 42.6°, one step (0.2°) at a time. Watch the **Light map**, its shares, the pavilion depth in the **Profile**, and the grade.\n3. **Find the window:** write down the first and the last pavilion angles that grade Excellent.\n4. Set **Chart view** to **Brilliance**. Watch the T73's marker move as you change the pavilion.\n5. Now set the table to 57% and the crown to 35.0°. Find the window again. Is it wider or narrower?\n\n## What the Cut Grading Tool shows\n\n**Too shallow.** At 39.4° the light map floods with blue: 36% contrast against the T73's 22%. A shallow pavilion sends back light from almost straight above. That is exactly where your head is, so the stone looks darker. Leakage is only 1%, but the grade is Good.\n\n**Too steep.** At 42.4° the blue shrinks to 7%, the green spreads to 30% and the leakage reaches 9% (13% at 42.6°). The stone now returns light from low, side angles and lets more light through the bottom.\n\n**The window.** Excellent goes from 40.6° to 41.4° at the T73's table and crown. At a 57% table and a 35.0° crown, it goes to 41.6°: a little wider, but never generous. The pavilion depth goes from about 41% at 39.4° to 46% at 42.6°.\n\n**The paradox.** The traced brilliance continues to climb past the window: 54.2% at 40.8°, 57.8% at 41.4°, 62.6% at 42.4°. So why does 42.4° grade Good? Because a grade is not light alone. The note in the tool says that it also weighs contrast and pattern, and these mark down very shallow and very deep pavilions. GIA's own examples say that steep stones are bright but have no strong, distinct pattern. A diamond with no contrast looks flat, even when it returns a lot of light.\n\nTolkowsky said it his way in 1919. A steeper pavilion would reflect more light, but it would cost the stone fire, and the trade isn't worth it. He chose 40°45'.\n\n## Key points\n\n- The pavilion angle sets the pavilion depth: half the diameter × tan(pavilion angle), about 43% at 40.8°.\n- The pavilion reflects light by total internal reflection. Light that meets a facet within 24.4° of square-on escapes.\n- A pavilion that is too shallow floods the face with your own reflection. A pavilion that is too steep returns low-angle light and leaks.\n- The Excellent window is narrow: 40.6° to 41.4° at the T73's table and crown.\n- More light is not the full story. Contrast and pattern count too, so the brightest pavilion in the sweep grades only Good.\n\n**Go further:** the [T57 cut page](https://digitalgemology.com/cuts/t57-round-brilliant) lists seven gemstones. For each one, it gives the critical angle and how much of the pavilion reflects head-on light.\n\n## Try it free\n\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/pavilion-angle-and-pavilion-depth)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n- [T57 Round Brilliant Cut](https://digitalgemology.com/cuts/t57-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Star length and lower half length in a round brilliant](https://digitalgemology.com/learn/diamond-anatomy/star-length-and-lower-half-length)\n- [Try another topic · Historic diamond cuts: the history of the brilliant: Hearts and arrows diamonds: precision you can see](https://digitalgemology.com/learn/historic-cuts/hearts-and-arrows-diamonds)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-anatomy/diamond-crown-angle) · [Diamond anatomy and proportions: all lessons](https://digitalgemology.com/learn/diamond-anatomy) · [All topics](https://digitalgemology.com/learn)"},{"id":"AOD-L6","course":"Anatomy of a diamond","lesson_number":6,"title":"Star length and lower half length in a round brilliant","url":"https://digitalgemology.com/learn/diamond-anatomy/star-length-and-lower-half-length","path":"/learn/diamond-anatomy/star-length-and-lower-half-length","markdown":"https://digitalgemology.com/learn/diamond-anatomy/star-length-and-lower-half-length.md","summary":"Lower half length and star length in a round diamond: what they measure, GIA's Excellent ranges, how they draw the hearts, and what painting costs.","queries":["lower half length diamond","star facet length","lower girdle facets"],"quiz":"https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/star-and-lower-half-lengths","tools":["https://digitalgemology.com/tools/hearts-and-arrows-scope","https://digitalgemology.com/tools/cut-grading-tool"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant","https://digitalgemology.com/cuts/t105-round-brilliant"],"text":"[Diamond anatomy and proportions](https://digitalgemology.com/learn/diamond-anatomy) · 4 min read\n\n# Star length and lower half length in a round brilliant\n\nLower half length is how far the lower half facets reach from the girdle toward the culet, as a percentage of that distance. GIA's Excellent range is 70 to 85% (star length: 45 to 65%), and longer lower halves give thinner hearts, further apart.\n\nVideo: [The T73 in the Hearts & Arrows Scope](https://www.youtube.com/watch?v=y7Lw8n9l0CM)\n\nThe T73 in the Hearts & Arrows Scope, arrows face up, turned over to the hearts. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nThe T73 in the Hearts & Arrows Scope, arrows face up, turned over to the hearts.\n\n## Sixteen small facets, one carat\n\nPicture a rough diamond that's going to come out at 0.99 ct. A hundredth short of the one-carat line, and a real step down in price.\n\nA cutter has a quiet trick. Tilt the small facets along the girdle (the upper halves, the lower halves or both) a little toward the big facets beside them. That leaves a touch more diamond at the girdle, and sometimes it's enough to cross the line. GIA's cut booklet calls it **painting**, and its opposite **digging out**. It notes that cutters can use both to save weight, for example to reach a round number like half a carat, one carat or two.\n\nThe price is the look. In our Cut Grading Tool, significant painting or digging takes a [T73](https://digitalgemology.com/cuts/t73-round-brilliant) down to Good, even when it's Excellent in every other way. Let's meet those small facets properly.\n\n![The T73 with significant painting and digging, graded Good.](https://digitalgemology.com/img/learn/aod-l6-cgt-painting-significant.webp?v=95e4506a)\n\nThe T73 with significant painting and digging, graded Good.\n\n## Two lengths\n\nThe [crown angle](https://digitalgemology.com/learn/diamond-anatomy/diamond-crown-angle) and the [pavilion angle](https://digitalgemology.com/learn/diamond-anatomy/diamond-pavilion-angle) belong to the big facets: bezels and mains. Two lengths set the small facets around them:\n\n- **Star length:** how far the star facets reach from the edge of the table toward the girdle, as a percentage of that distance. Long stars give smaller bezels.\n- **Lower half length:** how far the lower half facets reach from the girdle toward the culet, as a percentage of that distance. Long lower halves leave narrower pavilion mains.\n\nThe T73 has stars at 50% and lower halves at 77%. (The tool's slider moves in 5% steps, so it shows 75%.)\n\nFor an Excellent grade, GIA's limits are 45 to 65% for star length and 70 to 85% for lower half length. For Very Good, they are 40 to 70% and 65 to 90%. Past the Very Good ranges, GIA's tables allow any value at Good. So on their own, these two lengths can never take a stone below Good. Their job is the pattern: how the bright and dark slivers are arranged face up. (The tool's sliders stop at the Very Good limits. So in the tool, the worst you'll see is Very Good.)\n\n## The lower halves draw the hearts\n\nIn a Hearts & Arrows viewer, a well-made round shows eight arrows face up and eight hearts face down. The shaft of each arrow is a pavilion main reflected in the main opposite it, and the crown adds the arrowhead. You see each heart through the pavilion. It is made of six facet reflections: four from the pavilion mains make its body, and two half facets square off its top.\n\nThe lower halves decide their shape. Our Hearts & Arrows research notes say this:\n\n- lower halves of about 75% or less give fatter hearts with little gap between them;\n- 80% or more gives thinner hearts, further apart.\n\nIn the decades after 1919, cutters made the lower halves longer and the mains narrower. That change is what lets a modern round show hearts and arrows at all.\n\n### Try it yourself\n\n1. Open [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool). Open **More proportions**.\n2. Move **Star length** from 40% to 70% and watch the **Crown plan**. How do the stars and bezels change? Note where the grade changes.\n3. Do the same with **Lower half length**, 65% to 90%.\n4. Put both back. Set **Painting and digging** to Moderate, then Significant, then Severe.\n5. Open [Hearts & Arrows Scope](https://digitalgemology.com/tools/hearts-and-arrows-scope) with the **T73 Round Brilliant** in diamond. Then switch the cut to the **[T105 Round Brilliant](https://digitalgemology.com/cuts/t105-round-brilliant)**, which splits each lower half into three rows. Compare the hearts.\n\n## What the Cut Grading Tool and the H&A Scope show\n\n**The lengths.** Short stars (40%) leave big bezels and grade Very Good. From 45% to 65% the stone stays Excellent. At 70% it's Very Good again. Lower halves behave the same way: Very Good at 65% and 90%, Excellent between them. In the tool, these two lengths change the drawing and the grade. They do not change the light map or the brilliance, because the tool traces those on the T73's own star and lower half.\n\n**Painting and digging.** Moderate gives Very Good, Significant gives Good, Severe gives Fair. GIA's observations explain why. Given the choice, most viewers liked stones with only the slightest painting or digging, or none. Heavy painting on the pavilion breaks the pattern into broad dark zones. In the end, the round starts to look like the old single cut with its few facets. Heavy digging out can drain the contrast and leave a grayish stone. Cutters also dig out to grind away an inclusion near the girdle.\n\n**The hearts.** The T73 and the T105 have the same main angles, but their hearts look different. The T105's extra rows of small pavilion facets redraw them. Both read 100% symmetry. Symmetry tells you that the eight hearts match each other. The small facets decide what each heart looks like. The T73's own lower halves, at 77%, sit between the \"fat\" and \"thin\" heart lengths.\n\n![The hearts of the T73 and the T105 in the Hearts & Arrows Scope. The two cuts have the same main angles, but the T105's extra rows of small pavilion facets redraw the hearts.](https://digitalgemology.com/img/learn/aod-l6-t73-hearts-arrows.webp?v=f9bc9be1) ![The hearts of the T73 and the T105 in the Hearts & Arrows Scope. The two cuts have the same main angles, but the T105's extra rows of small pavilion facets redraw the hearts.](https://digitalgemology.com/img/learn/aod-l6-t105-hearts-arrows.webp?v=f95bd619)\n\nThe hearts of the T73 and the T105 in the Hearts & Arrows Scope. The two cuts have the same main angles, but the T105's extra rows of small pavilion facets redraw the hearts.\n\n## Key points\n\n- Star length and lower half length set the small facets around the bezels and mains. Each is a percentage of the distance that the facets span.\n- GIA's Excellent limits are 45 to 65% (star) and 70 to 85% (lower half). On their own, they can't take a stone below Good.\n- They shape the face-up pattern and the hearts, not the main angles. Longer lower halves give thinner hearts, further apart.\n- Painting and digging out tilt the half facets, often to save weight or to pass a carat threshold.\n- In the Cut Grading Tool, painting or digging lowers the grade: Moderate Very Good, Significant Good, Severe Fair.\n\n**Go further:** the [T105 cut page](https://digitalgemology.com/cuts/t105-round-brilliant) shows its extra star halves and three rows of lower halves.\n\n## Try it free\n\n- [Hearts & Arrows Scope](https://digitalgemology.com/tools/hearts-and-arrows-scope): See the arrows face up and the hearts face down as you change the cut.\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/star-and-lower-half-lengths)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n- [T105 Round Brilliant Cut](https://digitalgemology.com/cuts/t105-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Diamond girdle thickness: thin, medium, thick and what it costs you](https://digitalgemology.com/learn/diamond-anatomy/diamond-girdle-thickness)\n- [Try another topic · How to read a diamond grading report: What \"ideal cut\" means on a diamond report](https://digitalgemology.com/learn/grading-reports/what-ideal-cut-means)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-anatomy/diamond-pavilion-angle) · [Diamond anatomy and proportions: all lessons](https://digitalgemology.com/learn/diamond-anatomy) · [All topics](https://digitalgemology.com/learn)"},{"id":"AOD-L7","course":"Anatomy of a diamond","lesson_number":7,"title":"Diamond girdle thickness: thin, medium, thick and what it costs you","url":"https://digitalgemology.com/learn/diamond-anatomy/diamond-girdle-thickness","path":"/learn/diamond-anatomy/diamond-girdle-thickness","markdown":"https://digitalgemology.com/learn/diamond-anatomy/diamond-girdle-thickness.md","summary":"Diamond girdle thickness, from Extremely Thin to Extremely Thick: how it is judged, why thin chips and thick wastes weight, and what keeps Excellent.","queries":["diamond girdle thickness","faceted girdle","thick girdle diamond"],"quiz":"https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/the-girdle","tools":["https://digitalgemology.com/tools/cut-grading-tool","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant","https://digitalgemology.com/cuts/t57-round-brilliant"],"text":"[Diamond anatomy and proportions](https://digitalgemology.com/learn/diamond-anatomy) · 4 min read\n\n# Diamond girdle thickness: thin, medium, thick and what it costs you\n\nGirdle thickness is judged at the girdle's 16 valleys and reported as a range in eight words, from Extremely Thin to Extremely Thick. A thin girdle chips easily and a thick one adds weight that doesn't show face up; our T73 stays Excellent from 2.0% to 3.5%.\n\n## Ten percent heavier, and it doesn't show\n\nTwo round brilliants, side on, both 7.7 mm across. Same crown, same pavilion, same angles. One weighs 1.50 ct, the other 1.65 ct.\n\nThe only difference is a thin band around the middle. The [T57](https://digitalgemology.com/cuts/t57-round-brilliant), cut to Tolkowsky's 1919 proportions, has a knife-edge: the crown and the pavilion meet in a sharp line. The [T73](https://digitalgemology.com/cuts/t73-round-brilliant) has a girdle band of 16 small facets, the finish of most rounds today. That band makes the T73 about 10% heavier at the same width: at 8.15 mm, 1.99 ct against 1.81 ct.\n\nThat is weight you pay for and can't see face up. Now push it further. In our Cut Grading Tool, a thicker girdle on the T73, from 2.5% to 7.5%, takes it from Excellent to Fair. Not a single angle changes.\n\n![The T57 at 1.50 ct and the T73 at 1.65 ct, both 7.7 mm across, side on.](https://digitalgemology.com/img/learn/aod-l7-t57-vs-t73-same-width.webp?v=9c852504)\n\nThe T57 at 1.50 ct and the T73 at 1.65 ct, both 7.7 mm across, side on.\n\n## What the girdle is for\n\nThe **girdle** is the narrow band between the crown and the pavilion. It is the setting edge of the stone: the prongs grip it, and it takes the knocks. A girdle that is thick enough lowers the risk of damage. A girdle that is too thin chips easily. Labs also use the girdle as a place to write: a GIA report notes any inscription on the girdle, such as the report number.\n\nIts surface has three finishes. The thickness is graded the same way for all three:\n\n- **bruted:** left with the surface from the process that shapes the stone round;\n- **polished:** smooth;\n- **faceted:** cut into a row of small facets, like the T73's sixteen.\n\n## Valleys and hills\n\nThe girdle of a round is not an even band. The final faceting leaves it scalloped: **16 valleys**, where the upper and lower half facets come closest, and **16 hills** between them. The grader judges the thickness at the valleys, as a share of the diameter, from the thinnest to the thickest. So a report gives it as a range, such as \"Thin to Medium\", in eight steps:\n\n**Extremely Thin · Very Thin · Thin · Medium · Slightly Thick · Thick · Very Thick · Extremely Thick**\n\nA knife-edge, with no girdle at all, is called Extremely Thin. GIA's chart gives typical valley values for the others, for example about 1.8% for Medium and 7.5% for Extremely Thick. The lab also measures an average girdle thickness as a percentage with an optical device. The words come from a grader who looks at the stone in profile at 10x.\n\nBoth ends cost something. Too thin is a **durability** risk. Too thick adds weight that the stone doesn't show face up. GIA counts that against the stone as **weight ratio**: too much weight for the diameter. Part of this shows in the [total depth](https://digitalgemology.com/learn/diamond-anatomy/diamond-measurements-explained).\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator). Load the **T57 Round Brilliant**, turn on **Facet mesh** and set **View** to profile. Then load the **T73** and compare the edge.\n2. Open [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool). Under **More proportions**, move **Girdle thickness** from 1.0% to 8.0%. Watch the total depth in the **Profile**, and the grade with its **Limited by** line.\n3. **Find the safe zone:** the thinnest and the thickest girdle percentages that keep the T73 Excellent.\n4. Set **Girdle description** to each of the eight words, from Extremely thin to Extremely thick. Which ones allow Excellent?\n\n## What the simulator and the Cut Grading Tool show\n\n**The safe zone.** The T73 is Excellent from 2.0% to 3.5%. At 1.5% the girdle reads Very Thin and the grade is Very Good. At 1.0%, Extremely Thin, it's Good. At 4.0% the grade drops to Very Good. The cause is not the girdle itself but the total depth: 63.1%, just past the Excellent limit of 63.0%. At 5.5% it's Good, and at 7.5% it's Fair.\n\n**The words.** Thin, Medium and Slightly Thick allow Excellent. Very Thin and Thick limit the stone to Very Good. Extremely Thin and Very Thick limit it to Good, and Extremely Thick to Fair. The thin end is about durability. The thick end is about weight.\n\n**The T57 and T73.** Same angles, same face-up pattern. The T73's band adds depth (61.7% against 59.2%) and weight, and it gives the setter something to hold. The girdle always makes that trade.\n\n## Key points\n\n- The girdle is the setting edge. It must be thick enough to protect the stone, and thin enough not to waste weight.\n- It can be bruted, polished or faceted. The thickness is judged the same way.\n- The girdle of a round is scalloped into 16 valleys and 16 hills. The thickness is read at the valleys and reported as a range, in eight words from Extremely Thin to Extremely Thick.\n- A knife-edge counts as Extremely Thin. Very thin girdles are a durability risk. Thick girdles add weight that the face doesn't show.\n- In the Cut Grading Tool, the T73 stays Excellent from a 2.0% to a 3.5% girdle. At 7.5% it's Fair.\n\n**Go further:** the [T57](https://digitalgemology.com/cuts/t57-round-brilliant) and [T73](https://digitalgemology.com/cuts/t73-round-brilliant) cut pages give the depth and weight of both stones at the same 8.15 mm.\n\n## Try it free\n\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/the-girdle)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n- [T57 Round Brilliant Cut](https://digitalgemology.com/cuts/t57-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: The diamond culet: none, pointed or large](https://digitalgemology.com/learn/diamond-anatomy/diamond-culet)\n- [Try another topic · Historic diamond cuts: the history of the brilliant: Tolkowsky's 1919 ideal cut: the brilliant that was calculated](https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-anatomy/star-length-and-lower-half-length) · [Diamond anatomy and proportions: all lessons](https://digitalgemology.com/learn/diamond-anatomy) · [All topics](https://digitalgemology.com/learn)"},{"id":"AOD-L8","course":"Anatomy of a diamond","lesson_number":8,"title":"The diamond culet: none, pointed or large","url":"https://digitalgemology.com/learn/diamond-anatomy/diamond-culet","path":"/learn/diamond-anatomy/diamond-culet","markdown":"https://digitalgemology.com/learn/diamond-anatomy/diamond-culet.md","summary":"The diamond culet: what it is for, its eight sizes from None to Extremely Large, how a large culet shows face up, and what it does to the grade.","queries":["diamond culet","what is a culet","large culet diamond"],"quiz":"https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/the-culet","tools":["https://digitalgemology.com/tools/cut-grading-tool","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant","https://digitalgemology.com/cuts/mazarin"],"text":"[Diamond anatomy and proportions](https://digitalgemology.com/learn/diamond-anatomy) · 3 min read\n\n# The diamond culet: none, pointed or large\n\nThe culet is a tiny facet across the bottom point of the pavilion, parallel to the table, that protects the point from chipping. Reports give eight sizes, from None (pointed) to Extremely Large; Small or less allows Excellent, and Extremely Large drops our T73 to Poor.\n\n## The dark eye in the middle\n\nLook at a [Mazarin](https://digitalgemology.com/cuts/mazarin) face up. This mid-1600s cut was the first to be called a brilliant. Right in the center is a small dark spot, like the pupil of an eye. It's the bottom of the stone: a wide, open culet, seen straight through the table.\n\nNow look at our [T73](https://digitalgemology.com/cuts/t73-round-brilliant). No spot. Its pavilion mains meet in a point.\n\nIn 1919, Tolkowsky kept his culet tiny. In his view it had one job only: to stop the stone from ending in a needle point. Today our Cut Grading Tool reads GIA's tables and shows how much that point can matter. Give an otherwise Excellent T73 an extremely large culet, and it's graded **Poor**. The smallest facet on the stone can sink the grade on its own.\n\n![The Mazarin's open culet beside the T73's point, face up.](https://digitalgemology.com/img/learn/aod-l8-mazarin-vs-t73-face-up.webp?v=b6a84169)\n\nThe Mazarin's open culet beside the T73's point, face up.\n\n## What the culet is\n\nThe **culet** is a tiny facet polished across the bottom point of the pavilion, parallel to the table. Its job is protection: a sharp point can chip, especially on a loose stone.\n\nA report describes it in eight sizes:\n\n**None · Very Small · Small · Medium · Slightly Large · Large · Very Large · Extremely Large**\n\n\"None\" means that there's no culet facet. The eight mains meet in a point, which is often called **pointed**. And the little bottom facet must be parallel to the table. If it isn't, it is not a culet at all: the lab treats it as an extra facet and still writes None.\n\nLike the other proportions, the size is a percentage of the [average diameter](https://digitalgemology.com/learn/diamond-anatomy/diamond-measurements-explained). GIA's chart gives typical values for an octagonal culet: about 1.5% for Small, 3% for Medium, 7% for Large and 15% for Extremely Large. The smallest sizes are too fine to measure reliably. So the grader judges them by eye, face up through the table at 10x.\n\n## Why size matters face up\n\nFrom above, you look straight down through the table at the culet. A tiny culet disappears in the pattern. A large one shows as a spot in the very center, light or dark, as a result of what it reflects. It breaks up the pattern exactly where your eye goes first. That's why GIA counts culet size as part of the pattern of a stone.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator). Load the **Mazarin**, set **View** to face up and look at the center. Then load the **T73 Round Brilliant**.\n2. On the T73, turn on **Light map** and set the **Cut grade** to Poor. This gives it a culet 3.5% of the width. Look at the center of the map.\n3. Open [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool). Under **More proportions**, move **Culet** from None to Extremely large. Watch the **Crown plan**, the **Profile** and the grade.\n4. **Find the line:** which culet sizes still allow Excellent?\n\n## What the simulator and the Cut Grading Tool show\n\n**The spot.** Face up, the Mazarin's open culet shows as a dark eye in the center. On the light map it's a black dot: light that goes straight out through the bottom. The Poor T73, with a 3.5% culet, shows the same black dot in the middle of its map. The Excellent T73, with a point, has none.\n\n**The grade.** None, Very Small and Small allow Excellent. Medium limits the T73 to Very Good. Slightly Large and Large limit it to Good, Very Large to Fair, and Extremely Large to Poor. In the tool's crown plan, the culet appears through the table as a small octagon, and the profile becomes flat at the bottom.\n\n**Why so strict?** A culet does nothing for light. It only protects the point. So any size larger than protection needs is pure cost: a spot in the pattern, and nothing gained. One honest note: the tool traces its light map on the T73 with no culet, so use the simulator's map to see the spot.\n\n## Key points\n\n- The culet is a small facet across the point of the pavilion, parallel to the table. It is there to prevent chipping.\n- Reports describe it in eight sizes, from None (pointed) to Extremely Large, as a share of the average diameter.\n- Face up, through the table, a large culet shows as a spot in the center of the pattern.\n- The Mazarin of the 1600s had a wide, open culet. Tolkowsky, in 1919, kept it as small as possible.\n- In the Cut Grading Tool, Small or less allows Excellent. Extremely Large drops the T73 to Poor.\n\n**Go further:** the [Mazarin cut page](https://digitalgemology.com/cuts/mazarin) describes its open culet. The [T73 page](https://digitalgemology.com/cuts/t73-round-brilliant) shows a pointed one.\n\n## Try it free\n\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/the-culet)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n- [Mazarin Cut](https://digitalgemology.com/cuts/mazarin): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: How to read diamond proportions: decode a stone from its numbers](https://digitalgemology.com/learn/diamond-anatomy/how-to-read-diamond-proportions)\n- [Try another topic · Historic diamond cuts: the history of the brilliant: The Mazarin cut: the first brilliant](https://digitalgemology.com/learn/historic-cuts/mazarin-cut-diamond)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-anatomy/diamond-girdle-thickness) · [Diamond anatomy and proportions: all lessons](https://digitalgemology.com/learn/diamond-anatomy) · [All topics](https://digitalgemology.com/learn)"},{"id":"AOD-L9","course":"Anatomy of a diamond","lesson_number":9,"title":"How to read diamond proportions: decode a stone from its numbers","url":"https://digitalgemology.com/learn/diamond-anatomy/how-to-read-diamond-proportions","path":"/learn/diamond-anatomy/how-to-read-diamond-proportions","markdown":"https://digitalgemology.com/learn/diamond-anatomy/how-to-read-diamond-proportions.md","summary":"Ideal diamond proportions, by GIA's Excellent ranges for a round, and a six-step routine to decode a stone and find the number that holds it back.","queries":["ideal diamond proportions","round diamond proportions chart","diamond proportions explained"],"quiz":"https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/decode-a-stone","tools":["https://digitalgemology.com/tools/cut-grading-tool"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Diamond anatomy and proportions](https://digitalgemology.com/learn/diamond-anatomy) · 4 min read\n\n# How to read diamond proportions: decode a stone from its numbers\n\nFor a round brilliant, GIA's Excellent ranges are a total depth of 57.5 to 63%, a crown angle of 31.5° to 36.5° and a pavilion angle of 40.6° to 41.8°, graded as a pair with the table. The weakest number sets the grade.\n\n## Ten numbers, one grade\n\nHere's a round brilliant, as a report would describe it:\n\n| Table | Crown | Pavilion | Star | Lower half | Girdle | Culet | Polish | Symmetry |\n| --- | --- | --- | --- | --- | --- | --- | --- | --- |\n| 53% | 34.5° | 40.8° | 55% | 80% | 4.5%, Slightly Thick | Medium | Excellent | Excellent |\n\nThose are the [T73](https://digitalgemology.com/cuts/t73-round-brilliant)'s own angles, the ones Tolkowsky calculated in 1919. Is it Excellent?\n\nNo. It's Very Good, and two of those numbers decide it. At the end of this page you'll find them in seconds. Every stone on this page comes from a worked example in GIA's cut booklet. We'll decode four of them.\n\n![The stone above in the Cut Grading Tool, graded Very Good.](https://digitalgemology.com/img/learn/aod-l9-stone-b.webp?v=bf216757)\n\nThe stone above in the Cut Grading Tool, graded Very Good.\n\n## A decoding routine\n\nAll the proportions of a round fit into one routine. Use it on any set of proportions:\n\n1. **The depth sum.** Crown height + girdle + pavilion depth must come out close to the [total depth](https://digitalgemology.com/learn/diamond-anatomy/diamond-measurements-explained). A total depth over 63% says that the stone has extra weight. GIA's Excellent range is 57.5 to 63%.\n2. **The angle pair.** Check the crown (Excellent 31.5° to 36.5°) and the pavilion (40.6° to 41.8°). Remember that they're graded as a pair with the table (see our pages on the [table](https://digitalgemology.com/learn/diamond-anatomy/diamond-table-percentage), the [crown](https://digitalgemology.com/learn/diamond-anatomy/diamond-crown-angle) and the [pavilion](https://digitalgemology.com/learn/diamond-anatomy/diamond-pavilion-angle)). A pavilion near the edge of its range is the first suspect.\n3. **The edges.** [Girdle](https://digitalgemology.com/learn/diamond-anatomy/diamond-girdle-thickness): Thin to Slightly Thick allows Excellent. [Culet](https://digitalgemology.com/learn/diamond-anatomy/diamond-culet): Small or less.\n4. **The finish.** Polish and symmetry of Very Good or better allow Excellent. Good limits the stone to Very Good.\n5. **The small lengths.** Star 45 to 65% and lower half 70 to 85% allow Excellent. On their own, they can never pull a stone below Good (see [star and lower half lengths](https://digitalgemology.com/learn/diamond-anatomy/star-length-and-lower-half-length)).\n6. **The weakest wins.** The grade is the lowest of all the checks above. Find that one number, and you've decoded the stone.\n\n### Try it yourself\n\nEnter each stone in [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool). (Open **More proportions** for the girdle, culet and finish.) Predict the grade *before* you look. Then check the **Limited by** line.\n\n| Stone | Table | Crown | Pavilion | Star | Lower half | Girdle | Culet | Polish | Symmetry |\n| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |\n| A | 57% | 35.5° | 40.8° | 55% | 80% | 3.0% | None | Excellent | Very Good |\n| B | 53% | 34.5° | 40.8° | 55% | 80% | 4.5%, Slightly Thick | Medium | Excellent | Excellent |\n| C | 53% | 32.0° | 42.8° | 55% | 80% | 3.5% | None | Excellent | Excellent |\n\n**The mystery stone, D:** 61% table, 33.0° crown, 41.2° pavilion, star 55%, lower half 80%, girdle 2.5%, culet None, polish Very Good, symmetry Excellent. A 61% table is big. Excellent or not? Make your prediction before you check.\n\n## What the Cut Grading Tool shows\n\n**Stone A: Excellent.** Crown height 15.3%, girdle 3.0%, pavilion depth 43.2%. With the tool's small calibration, that gives a total depth of about 61.2%. Every check passes. The symmetry is only Very Good, but a Very Good finish still allows Excellent.\n\n**Stone B: Very Good.** The angles are the T73's, so the pair is fine. The depth sum shows the problem: 16.2 + 4.5 + 43.2, less the tool's small calibration, makes about 63.6%, past 63%. And the Medium culet also limits it to Very Good. Two numbers, both about the edges. Face up, you might not see a difference from an Excellent stone. The problem is the extra weight that it hides below the girdle. GIA's own note on this example says the same.\n\n**Stone C: Good.** The crown is shallow but allowed. The pavilion, 42.8°, is past the Excellent limit of 41.8° and even past the Very Good limit of 42.4°. It's a steep pavilion. GIA's example calls the stone fairly bright, but with no strong, distinct pattern. The light map agrees: green at 22%, blue down to 7%.\n\n**Stone D: Excellent.** A 61% table, and still Excellent: its flatter crown and slightly steeper pavilion balance the big table. Large tables leave little room, as our page on [table percentage](https://digitalgemology.com/learn/diamond-anatomy/diamond-table-percentage) shows, but there is some.\n\n## Key points\n\n- Total depth must match crown height + girdle + pavilion depth. Over 63% means extra weight.\n- The crown and the pavilion are judged as a pair with the table. The pavilion is the most sensitive.\n- The girdle and the culet are the \"edges\". Thick girdles and big culets limit a stone, even with perfect angles.\n- Polish and symmetry of Very Good or better allow Excellent. Star and lower half lengths alone can't pull a stone below Good.\n- The grade is the weakest of all of them. Find that one number, and you've decoded the stone.\n\n**Go further:** take the [diamond anatomy quiz](https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond). It tests everything from the three parts to the culet.\n\n## Try it free\n\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/anatomy-of-a-diamond/decode-a-stone)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Try another topic · The four Cs of diamonds: How a diamond cut grade is set: proportions, polish and symmetry](https://digitalgemology.com/learn/four-cs/how-diamond-cut-grade-is-determined)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-anatomy/diamond-culet) · [Diamond anatomy and proportions: all lessons](https://digitalgemology.com/learn/diamond-anatomy) · [All topics](https://digitalgemology.com/learn)"},{"id":"GR-L1","course":"Reading a grading report","lesson_number":1,"title":"What a diamond grading report is, and what it isn't","url":"https://digitalgemology.com/learn/grading-reports/what-is-a-diamond-grading-report","path":"/learn/grading-reports/what-is-a-diamond-grading-report","markdown":"https://digitalgemology.com/learn/grading-reports/what-is-a-diamond-grading-report.md","summary":"What a diamond grading report is and what it isn't: not an appraisal, GIA's main report types, and the five parts that every diamond report has.","queries":["diamond grading report","diamond certificate vs appraisal","gia report"],"quiz":"https://digitalgemology.com/skool/quiz/reading-a-grading-report/what-a-grading-report-is","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":[],"text":"[How to read a diamond grading report](https://digitalgemology.com/learn/grading-reports) · 3 min read\n\n# What a diamond grading report is, and what it isn't\n\nA diamond grading report is an independent lab's record of what a stone is and how it grades on the day the lab examined it. It is not an appraisal: it says what the stone is, not what it is worth.\n\n## Two stones, one sheet of paper\n\nTwo loose diamonds of the same size can look identical. A grading report tells them apart. It records what the stone is, how it grades and how to recognize it again. A lab with no stake in the sale writes it: GIA doesn't buy or sell diamonds.\n\n## What a report is, and what it isn't\n\nA report is a lab's record of the stone on the day the lab examined it. It records:\n\n- whether the stone is natural or laboratory-grown\n- whether it is treated\n- its four Cs, its measurements and its proportions.\n\nIt is **not an appraisal**: it tells you what the stone is, not what it is worth.\n\n## GIA's main report types\n\n- **Diamond Grading Report**: for loose natural diamonds of 0.15 carat and up. It gives the four Cs, a plotted diagram of the clarity characteristics and a drawing of the proportions. Round brilliants in the D-to-Z color range also get a cut grade.\n- **Diamond Dossier**: for loose natural diamonds from 0.15 to 1.99 carats in the D-to-Z range. It gives the same grades and proportions, without the clarity plot. The report number is laser-inscribed on the girdle.\n- **Laboratory-Grown Diamond Quality Assessment**: for lab-grown diamonds. Since 1 October 2025, GIA rates a colorless to near-colorless lab-grown diamond Premium or Standard, with no D-to-Z color or clarity grade. Before that, GIA's digital Laboratory-Grown Diamond Report graded lab-grown diamonds on the same principles as natural ones.\n- **Identification Report**: for simulants such as cubic zirconia, and for diamonds with unstable treatments such as coating or fracture filling. GIA doesn't issue a grading report for those.\n\nGIA can also add a supplement, the **AGS Ideal Report by GIA**, with a separate light performance grade. [What \"ideal cut\" means on a diamond report](https://digitalgemology.com/learn/grading-reports/what-ideal-cut-means) explains how it differs from the cut grade. GIA also issues colored stone reports. These identify the gem and any treatment, and some also give a geographic origin.\n\n**On an IGI report:** IGI also reports on stones set in jewelry, \"as mounting permits\". Then color and clarity become a range, such as D–E, with an estimated cut grade. GIA's diamond grading reports are for loose stones only.\n\n## The five parts of a report\n\nEvery diamond report, from either lab, has the same five parts:\n\n1. **Identity**: date, report number, shape and cutting style, measurements.\n2. **Grades**: carat weight, color, clarity and, where given, cut.\n3. **Additional grading**: polish, symmetry, fluorescence, inscriptions, comments.\n4. **Diagrams**: the proportion profile and, on a full report, the clarity plot.\n5. **Checks**: the grading scales, security features and a QR code to verify the report online.\n\n![Our simulator's PDF report with the five parts outlined, each in its own color.](https://digitalgemology.com/img/learn/gr-l1-report-five-parts.webp?v=2019e462)\n\nOur simulator's PDF report with the five parts outlined, each in its own color.\n\n### Try it yourself\n\nOur simulator writes a report for the stone on screen, with the same layout. It is a learning tool, not a lab report.\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the round brilliant in diamond.\n2. In the report, find the **identity** part: date, simulation number, shape and cutting style, measurements.\n3. Find the **grades**, then the **additional grading**: polish, symmetry, fluorescence.\n4. Scroll to the **proportions** and the **QR code**.\n5. Change the color grade to H. Which lines of the report change, and which stay the same?\n\n## What the simulator's report shows\n\nOnly the color line changed. Shape, measurements and proportions stayed the same, as on a real report. The identity part describes this stone and no other. The grades describe its quality.\n\n## Key points\n\n- A grading report is an independent lab's record of what a stone is and how it grades on the day the lab examined it.\n- A report is not an appraisal: it says what the stone is, not what it is worth.\n- GIA's main diamond reports are the Diamond Grading Report, the Diamond Dossier, the Laboratory-Grown Diamond Quality Assessment (since 1 October 2025) and the Identification Report.\n- Every diamond report has five parts: identity, grades, additional grading, diagrams and checks.\n\n**Go further:** [the ID section of a report](https://digitalgemology.com/learn/grading-reports/diamond-report-identity-section): how to make sure a report belongs to the stone in front of you.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/reading-a-grading-report/what-a-grading-report-is)\n\n## Keep exploring\n\n- [Next lesson: The ID section of a diamond report: number, shape and measurements](https://digitalgemology.com/learn/grading-reports/diamond-report-identity-section)\n- [Try another topic · Diamond anatomy and proportions: Crown angle and crown height in a round diamond](https://digitalgemology.com/learn/diamond-anatomy/diamond-crown-angle)\n\n[How to read a diamond grading report: all lessons](https://digitalgemology.com/learn/grading-reports) · [All topics](https://digitalgemology.com/learn)"},{"id":"GR-L2","course":"Reading a grading report","lesson_number":2,"title":"The ID section of a diamond report: number, shape and measurements","url":"https://digitalgemology.com/learn/grading-reports/diamond-report-identity-section","path":"/learn/grading-reports/diamond-report-identity-section","markdown":"https://digitalgemology.com/learn/grading-reports/diamond-report-identity-section.md","summary":"How to read a diamond certificate's ID section: report number, shape, measurements and carat weight, and how to check that the report fits the stone.","queries":["how to read a diamond certificate","gia report number","diamond measurements on report"],"quiz":"https://digitalgemology.com/skool/quiz/reading-a-grading-report/who-is-this-stone","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant","https://digitalgemology.com/cuts/oval"],"text":"[How to read a diamond grading report](https://digitalgemology.com/learn/grading-reports) · 4 min read\n\n# The ID section of a diamond report: number, shape and measurements\n\nTo read a diamond certificate, start with the identity block: date, report number, shape and cutting style, and measurements. With the carat weight, these lines tie the report to one stone, because a given cut in a given material has only one size at a given weight.\n\n## The stone that's too wide\n\nA report reads: **round brilliant, 1.00 carat, 6.48 – 6.50 × 4.00 mm**. The stone it came with weighs exactly 1.00 carat on your scale. But your gauge says it's **6.67 mm** across.\n\nA few hundredths of a millimeter could be measuring error. Seventeen to nineteen hundredths at the same weight is not. Something here isn't the stone on the report.\n\nOur simulator shows exactly this difference. A 1.00 ct [T73](https://digitalgemology.com/cuts/t73-round-brilliant) in diamond measures 6.48 mm. The same cut at the same weight in moissanite measures 6.67 mm, because moissanite is less dense. Same carat, wider stone. The identity block caught it, and you didn't need a single grade to do it.\n\n![1.00 ct in diamond and in moissanite, at true size.](https://digitalgemology.com/img/learn/gr-l2-t73-diamond-vs-moissanite-measurements.webp?v=d8c797df)\n\n1.00 ct in diamond and in moissanite, at true size.\n\n## The identity block\n\nThe top of a GIA report describes *this* stone and no other. (The carat weight sits with the grades, but the identity check uses it too.)\n\n- **Date:** the day the lab examined the stone. Everything on the report is true on that day.\n- **Report number:** unique, and registered in GIA's database.\n- **Shape and cutting style:** the outline (round, oval, pear…) and the pattern of facets (brilliant, step cut…), such as \"Round Brilliant\".\n- **Measurements:** for a round, *minimum diameter – maximum diameter × depth*; for a fancy shape, *length × width × depth*, in millimeters.\n- **Carat weight**, from the grades block: to the hundredth of a carat. GIA's balance reads to the fifth decimal place, and the report rounds to two.\n\nWeight and measurements together are a powerful check. A given cut in a given material has only one size at a given weight. If the millimeters don't fit the carats, ask why.\n\n## Checking a report\n\nA report is only useful if it belongs to the stone. GIA gives you several ways to check:\n\n- **Inscription.** Many stones carry their report number on the girdle. A laser writes it, and you can see it under magnification. The report lists any inscription. On a Diamond Dossier the number is always inscribed.\n- **Report Check.** Enter the number on GIA's Report Check, or scan the report's **QR code**. You then see what GIA itself recorded. For digital reports, that online version is the definitive one.\n- **Security features.** The printed report carries microprinting, security screens, watermarks, a two-dimensional barcode, a hologram and sheet numbering.\n\n**On an IGI report:** IGI calls its inscription **Laserscribe**, and says it co-created the modern laser inscription process. Every laboratory-grown diamond IGI grades is inscribed automatically, with **\"LG\"** before the report number. Natural diamonds are inscribed when the owner asks. IGI's balance reads to four decimals (GIA's to five), and both report the weight to two. The QR code and IGI's **Verify Your Report** page lead to the online copy, and the paper report has at least five security features. Grading is anonymous: IGI masks the owner details and gives each stone an internal number.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the T73 Round Brilliant in diamond. Find **Date**, **Simulation number**, **Shape and cutting style** and **Measurements** at the top of its report.\n2. Step **Carat weight** from 0.5 to 2. Write down the measurements line at each step.\n3. Back at 1.00 ct, change **Gemstone** to moissanite. Read the measurements again.\n4. Change the cut to the **[Oval](https://digitalgemology.com/cuts/oval)**. How does the form of the measurements line change?\n5. **Catch the swap:** a report says 1.00 ct, 6.47 – 6.49 × 4.00 mm. You have three stones on your desk, all 1.00 ct. They measure 6.48 × 4.00, 6.67 × 4.12 and 6.16 × 4.16 mm. Which one belongs to the report, and what might the other two be?\n\n## What the simulator shows\n\n**Carat and millimeters move together.** At 0.50 ct the T73 measures 5.14 mm, at 1.00 ct 6.48 mm, at 2.00 ct 8.16 mm. One weight, one size, for one cut in one material.\n\n**The material shows.** In moissanite the same 1.00 ct is 6.67 – 6.67 × 4.12 mm: 3% wider and deeper, because each carat is more stone.\n\n**The form changes with the shape.** For the oval the line becomes length × width × depth, because a fancy shape has no single diameter.\n\n**Catch the swap.** The 6.48 × 4.00 mm stone fits the report. The 6.67 × 4.12 mm stone is the right weight but too big all round. It could be a less dense material, like moissanite. The 6.16 × 4.16 mm stone is narrower and deeper: a heavier-bottomed, worse-cut stone. Only the first one is the stone on the paper. A mismatch doesn't prove what a stone *is*, but it proves the report isn't its own.\n\nThe simulator's report is for learning, not a lab report. Its \"simulation number\" is not a report number.\n\n## Key points\n\n- The identity block (date, report number, shape and cutting style, measurements) describes one stone on one day. With the carat weight, it ties the paper to the stone.\n- Rounds give minimum – maximum diameter × depth; fancy shapes give length × width × depth.\n- Weight and measurements must agree: a given cut in a given material has one size at one weight.\n- Check a report with the girdle inscription, the lab's online database (QR code, Report Check or Verify Your Report) and the paper's security features.\n- IGI inscribes every lab-grown stone with \"LG\" before the number; natural stones on request.\n\n**Go further:** [how to turn the measurements line into a total depth percentage](https://digitalgemology.com/learn/diamond-anatomy/diamond-measurements-explained).\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/reading-a-grading-report/who-is-this-stone)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n- [Oval Cut](https://digitalgemology.com/cuts/oval): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: The grades on a diamond report: color, clarity and cut](https://digitalgemology.com/learn/grading-reports/diamond-report-grades)\n- [Try another topic · The bow-tie effect: How to check a stone for a bow-tie: a bench routine](https://digitalgemology.com/learn/bow-tie/how-to-check-a-diamond-for-a-bow-tie)\n\n[Previous lesson](https://digitalgemology.com/learn/grading-reports/what-is-a-diamond-grading-report) · [How to read a diamond grading report: all lessons](https://digitalgemology.com/learn/grading-reports) · [All topics](https://digitalgemology.com/learn)"},{"id":"GR-L3","course":"Reading a grading report","lesson_number":3,"title":"The grades on a diamond report: color, clarity and cut","url":"https://digitalgemology.com/learn/grading-reports/diamond-report-grades","path":"/learn/grading-reports/diamond-report-grades","markdown":"https://digitalgemology.com/learn/grading-reports/diamond-report-grades.md","summary":"The grades on a diamond certificate: how color, clarity and cut are written, what an asterisk means, and which stones get a cut grade at GIA and IGI.","queries":["diamond certificate grades","gia grading scale","diamond report grades explained"],"quiz":"https://digitalgemology.com/skool/quiz/reading-a-grading-report/the-grades","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator","https://digitalgemology.com/tools/cut-grading-tool"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant","https://digitalgemology.com/cuts/oval"],"text":"[How to read a diamond grading report](https://digitalgemology.com/learn/grading-reports) · 4 min read\n\n# The grades on a diamond report: color, clarity and cut\n\nA diamond report grades color from D to Z, clarity from Flawless to I3 at 10x, and cut from Excellent to Poor. GIA gives a cut grade only to standard round brilliants in the D-to-Z range, and an asterisk after the color grade means a detected color treatment.\n\n## One small star\n\nOn a GIA report, the color grade of one stone reads **F***. The asterisk is a single character, smaller than the letter beside it. It means the lab detected a **color treatment**, and the Comments section will say what. For example, a diamond can be heated under enormous pressure (HPHT) to remove or change its color.\n\nThis page trains your eye for that kind of thing. The grade lines look simple: a letter, a few capitals, a word. But each one follows rules. Once you know them, you can tell at a glance whether a line makes sense.\n\n## How a report writes the grades\n\n- **Carat weight:** to the hundredth (see [the ID section of a report](https://digitalgemology.com/learn/grading-reports/diamond-report-identity-section)).\n- **Color grade:** a letter from **D** (colorless) to **Z** (light yellow or brown). The grader compares the stone with GIA's master color diamonds. An ***** means the lab detected a color treatment, and Comments explains it.\n- **Clarity grade:** from **Flawless** to **I3**, set at 10x magnification. The grade comes from the size, nature, number, position and relief of the clarity characteristics.\n- **Cut grade:** from **Excellent** to **Poor**. It combines face-up appearance, design and craftsmanship. GIA gives it only to **standard round brilliants in the D-to-Z color range**. A fancy shape, or a fancy-color diamond, has no GIA cut grade, and that's not a defect.\n\nFor the meaning behind each grade, see [the four Cs of diamonds](https://digitalgemology.com/learn/four-cs). Here we care about how a report writes the grades and where they can appear.\n\n**On an IGI report:** IGI also grades color D to Z against master stones, with several gemologists grading independently. It groups the letters into named bands (for example G–J, Near Colorless). IGI grades the cut of **fancy shapes** too, Excellent to Poor, as an option. To earn Excellent, a fancy shape has to clear four hurdles in turn:\n\n- polish and symmetry both Very Good or better\n- proportions inside IGI's published ranges for that shape\n- shape-specific checks such as bow-ties and girdle ranges\n- finally, a gemologist's judgment of its light return.\n\nFor rounds, IGI's top cut grade is Excellent, with an \"Ideal\" comment for the best (see [what \"ideal cut\" means](https://digitalgemology.com/learn/grading-reports/what-ideal-cut-means)). Its round chart publishes one range per proportion for each grade. GIA has individual limits too, but it also grades the table, crown and pavilion angle in combination. And on an IGI round, a visible **fish-eye** caps the cut grade at Fair.\n\n![Two stones whose GIA reports differ in one line: only the round has a cut grade.](https://digitalgemology.com/img/learn/gr-l3-t73-d-fl-vs-oval-h-vs2.webp?v=55dd42e3)\n\nTwo stones whose GIA reports differ in one line: only the round has a cut grade.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator). Build **stone A**: [T73 Round Brilliant](https://digitalgemology.com/cuts/t73-round-brilliant), diamond, 1.00 ct, color D, clarity FL, cut Excellent. Write its grade lines the way a GIA report would.\n2. Build **stone B**: the **[Oval](https://digitalgemology.com/cuts/oval)**, color H, clarity VS2. Write its lines. Which line would a GIA report leave out?\n3. Build **stone C**: the T73 again, with **Color scale** switched to **Fancy color**, **Yellow**, **Intense**. Which line would a GIA report leave out now?\n4. **Spot the impossible.** Which of these GIA grade lines can't be real?\n  - Round Brilliant · 1.02 ct · G · VS1 · Cut Excellent\n  - Oval · 1.50 ct · E · VVS2 · Cut Excellent\n  - Round Brilliant · 0.90 ct · Fancy Vivid Yellow · SI1 · Cut Very Good\n  - Round Brilliant · 2.01 ct · J* · SI2 · Cut Good\n\n## What the simulator shows\n\n**Stone A** reads 1.00 ct, D, FL, Excellent: every line filled. **Stone B**, the oval, would get color and clarity on a GIA report, but no cut grade. GIA doesn't grade the cut of fancy shapes. **Stone C**, a fancy yellow, is off the D-to-Z scale. So it doesn't qualify for GIA's cut grade either, even as a round.\n\nOne simulator note: our simulator shows a **Cut grade** control on the oval and on the fancy yellow too. The reason: its cut grade is a fixed schedule of worse proportions that you can apply to many shapes and colors. It is not a lab grade. A GIA report wouldn't print one for either stone. The simulator is a learning tool, not a lab report.\n\n**Spot the impossible.** The oval with \"Cut Excellent\" can't be a GIA report (it could be an IGI one). The Fancy Vivid Yellow round with a cut grade can't be GIA either: cut grades stop at D to Z. The first line is fine. The last is fine too: J* is a treated J, explained in Comments.\n\n## Key points\n\n- Color is D to Z against master diamonds. An asterisk after the grade means a detected color treatment, explained in Comments.\n- Clarity runs Flawless to I3, judged at 10x on size, nature, number, position and relief.\n- GIA gives a cut grade only to standard round brilliants in the D-to-Z range. Fancy shapes and fancy colors have none.\n- IGI also grades fancy-shape cut (optional; four checks to earn Excellent) and publishes one range per round proportion per grade.\n- An IGI round with a visible fish-eye can't grade above Fair.\n\n**Go further:** [the four Cs of diamonds](https://digitalgemology.com/learn/four-cs) explains what each grade means for the stone you see.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/reading-a-grading-report/the-grades)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n- [Oval Cut](https://digitalgemology.com/cuts/oval): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: What \"ideal cut\" means on a diamond report](https://digitalgemology.com/learn/grading-reports/what-ideal-cut-means)\n- [Try another topic · The bow-tie effect: Is a bow-tie always there? How much is normal](https://digitalgemology.com/learn/bow-tie/is-a-bow-tie-always-present)\n\n[Previous lesson](https://digitalgemology.com/learn/grading-reports/diamond-report-identity-section) · [How to read a diamond grading report: all lessons](https://digitalgemology.com/learn/grading-reports) · [All topics](https://digitalgemology.com/learn)"},{"id":"GR-L4","course":"Reading a grading report","lesson_number":4,"title":"What \"ideal cut\" means on a diamond report","url":"https://digitalgemology.com/learn/grading-reports/what-ideal-cut-means","path":"/learn/grading-reports/what-ideal-cut-means","markdown":"https://digitalgemology.com/learn/grading-reports/what-ideal-cut-means.md","summary":"What \"ideal cut\" means on a diamond report: a comment on an Excellent cut at IGI, a light performance grade on the AGS Ideal supplement at GIA.","queries":["ideal cut diamond","ideal vs excellent cut","ags ideal"],"quiz":"https://digitalgemology.com/skool/quiz/reading-a-grading-report/what-ideal-means","tools":["https://digitalgemology.com/tools/cut-grading-tool","https://digitalgemology.com/tools/3d_gemstone_simulator","https://digitalgemology.com/tools/hearts-and-arrows-scope"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[How to read a diamond grading report](https://digitalgemology.com/learn/grading-reports) · 4 min read\n\n# What \"ideal cut\" means on a diamond report\n\nOn an IGI report, \"Ideal\" is a comment on an Excellent round whose every proportion sits in a narrower middle band. On a GIA report, the cut grade stops at Excellent, and \"AGS Ideal\" is a separate light performance grade on a supplement.\n\n## One word, three meanings\n\n\"Ideal cut\" is everywhere in diamond selling. On paper it means three different things:\n\n- On an **IGI** report, \"Ideal\" is a **comment** added to an Excellent cut grade, for rounds whose proportions sit in a narrower middle band.\n- On a **GIA** report, the cut grade stops at **Excellent**. \"Ideal\" appears only on a separate supplement, the **AGS Ideal Report by GIA**, as a **light performance** grade.\n- In a sales pitch, it can mean anything.\n\nAnd here's the surprise. Our Cut Grading Tool reads GIA's published tables. Take the [T73](https://digitalgemology.com/cuts/t73-round-brilliant)'s table and crown in the tool, and set the pavilion to 40.4°. The tool says **Very Good**. Now check the same numbers against IGI's published chart: every one of them sits inside IGI's **Ideal** band. By the two published charts, the same proportions could earn \"Ideal\" at one lab and Very Good on the other's tables. Let's see how.\n\n![Pavilion 40.4°, Very Good on GIA's tables, inside IGI's Ideal band.](https://digitalgemology.com/img/learn/gr-l4-cgt-pavilion-40.4.webp?v=36437706)\n\nPavilion 40.4°, Very Good on GIA's tables, inside IGI's Ideal band.\n\n## Ideal at IGI: a comment on Excellent\n\nIGI's cut chart for round brilliants gives every proportion its own range for each grade. The top grade is **Excellent**. Inside the Excellent ranges sits a narrower middle band. A stone with every proportion in that band gets the comment **\"Ideal Cut Round Brilliant\"** (IGI's pages call it \"Excellent-Ideal\"). The band, from IGI's May 2023 chart:\n\n| Proportion | IGI \"Ideal\" band |\n| --- | --- |\n| Total depth | 58.5 to 62.5% |\n| Table | 53 to 60% |\n| Crown angle | 33 to 36° |\n| Crown height | 13 to 16.5% |\n| Pavilion angle | 40.0 to 41.3° |\n| Pavilion depth | 42 to 44% |\n| Girdle | Thin to Slightly Thick |\n| Polish and symmetry | at least Very Good |\n\n## Ideal at GIA: a light performance grade\n\nGIA's cut grade (Excellent to Poor) is about proportions, design and craftsmanship. Light performance is a separate measure, from the American Gem Society. The AGS is a nonprofit trade association, founded in 1934 by the same founders as GIA. The **AGS Ideal Report by GIA** is a supplement to a GIA report, with a light performance grade from 0 to 10. **AGS Ideal 0** is the top, and GIA issues the supplement only for stones that reach it. Brightness, fire and contrast each get a grade too, and the report can include an **ASET** map.\n\nTo be eligible, a round must first be a GIA \"Triple Excellent\": Excellent cut, polish and symmetry. Even then, most don't qualify. GIA notes that the AGS method is quite different from its cut grade. It also notes that few diamonds have both the optical precision and the light return to reach grade 0.\n\n**On an IGI report:** IGI has its own **Light Performance Report** for rounds with top optical performance. It gives a Light Performance score plus Brightness, Fire and Contrast, and an Ideal-Scope image made by ray tracing. The report uses only the stone's external proportions, so it doesn't account for heavy inclusions. IGI also issues **Hearts & Arrows** reports. These are for stones cut precisely enough to show eight hearts face down and eight arrows face up in a reflective scope.\n\n### Try it yourself\n\n1. Open [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool). The T73 as cut: 53%, 34.5°, 40.8°. Check each of its numbers in the **Profile** against IGI's Ideal band above. Does it fit?\n2. Set the **Pavilion angle** to 40.4°. What does the tool say? Check the band again.\n3. Set it to 41.4°. Tool, then band.\n4. **Find the overlap:** at the T73's table and crown, which pavilion angles are Excellent in the tool *and* inside IGI's Ideal band?\n5. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator), T73 in diamond, and turn on **Light map**. Compare its colors with an ASET map's (below). Then open [Hearts & Arrows Scope](https://digitalgemology.com/tools/hearts-and-arrows-scope).\n\n## What the tools show\n\n**The T73 fits both.** Table 53%, crown 34.5° and about 16% high, pavilion 40.8° and about 43% deep, total depth about 61.6%, girdle 2.5%. Every number is inside IGI's Ideal band, and the tool says Excellent.\n\n**At 40.4°** the tool drops to Very Good: GIA's tables want 40.6° or more at this table and crown. IGI's Ideal band starts at 40.0°, and the pavilion depth (about 42.6%) still fits. **At 41.4°** it's the other way round. The tool still says Excellent. But 41.4° is past IGI's 41.3°, and the pavilion depth (about 44.1%) is past 44%. So IGI would drop the Ideal comment. **The overlap** is 40.6° to 41.2° (in the tool's 0.2° steps).\n\nThat's our tool reading GIA's tables, and our reading of IGI's chart: neither is a lab's grade. But it shows why \"Ideal\" and \"Excellent\" aren't interchangeable: the labs draw their lines differently.\n\n**The colors.** An ASET map uses four colors:\n\n- **Red** marks where the stone returns its strongest light.\n- **Green** marks where it returns dimmer light that still adds sparkle.\n- **Blue** marks the dark contrast areas that give the pattern its shape.\n- **Gray** marks light lost through the bottom.\n\nA stone that scores well is mostly red, with blue spread evenly and only small touches of green and gray. Our simulator's Light Return map uses the same idea, with black for leakage. It's our own render, not an ASET.\n\n## Key points\n\n- At IGI, \"Ideal\" is a comment on an Excellent round whose every proportion fits a narrower band (IGI's pages say \"Excellent-Ideal\").\n- At GIA, the cut grade tops out at Excellent. \"AGS Ideal\" is a separate light performance grade on a supplement, and only for stones that reach grade 0.\n- A GIA Triple Excellent doesn't automatically qualify for AGS Ideal.\n- The labs draw their lines differently. By the published charts, a pavilion of 40.4° can sit inside IGI's Ideal band and still be Very Good on GIA's tables.\n- Light performance reports (AGS and IGI) score brightness, fire and contrast. An ASET map shows red, green, blue and gray.\n\n**Go further:** [how the pavilion, the most sensitive number on a round, moves the grade](https://digitalgemology.com/learn/diamond-anatomy/diamond-pavilion-angle).\n\n## Try it free\n\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n- [Hearts & Arrows Scope](https://digitalgemology.com/tools/hearts-and-arrows-scope): See the arrows face up and the hearts face down as you change the cut.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/reading-a-grading-report/what-ideal-means)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Polish, symmetry and fluorescence on a diamond report](https://digitalgemology.com/learn/grading-reports/polish-symmetry-and-fluorescence)\n- [Try another topic · Diamond anatomy and proportions: Star length and lower half length in a round brilliant](https://digitalgemology.com/learn/diamond-anatomy/star-length-and-lower-half-length)\n\n[Previous lesson](https://digitalgemology.com/learn/grading-reports/diamond-report-grades) · [How to read a diamond grading report: all lessons](https://digitalgemology.com/learn/grading-reports) · [All topics](https://digitalgemology.com/learn)"},{"id":"GR-L5","course":"Reading a grading report","lesson_number":5,"title":"Polish, symmetry and fluorescence on a diamond report","url":"https://digitalgemology.com/learn/grading-reports/polish-symmetry-and-fluorescence","path":"/learn/grading-reports/polish-symmetry-and-fluorescence","markdown":"https://digitalgemology.com/learn/grading-reports/polish-symmetry-and-fluorescence.md","summary":"Diamond polish and symmetry on a report, from Excellent to Poor, how they cap a round's cut grade, and what fluorescence \"None\" really means.","queries":["diamond polish and symmetry","excellent polish very good symmetry","fluorescence on gia report"],"quiz":"https://digitalgemology.com/skool/quiz/reading-a-grading-report/polish-symmetry-and-fluorescence","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator","https://digitalgemology.com/tools/hearts-and-arrows-scope","https://digitalgemology.com/tools/cut-grading-tool"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[How to read a diamond grading report](https://digitalgemology.com/learn/grading-reports) · 4 min read\n\n# Polish, symmetry and fluorescence on a diamond report\n\nPolish grades the smoothness of the facet surfaces, and symmetry the exactness of the outline and the facets, both from Excellent to Poor. On a GIA round, Good polish or symmetry caps the cut grade at Very Good, Fair at Good, and Poor at Poor.\n\n## The small print that vetoes the cut\n\nBelow the big four grades, a report has three short lines: polish, symmetry, fluorescence. They look like footnotes. They aren't.\n\nTake a round with every proportion in GIA's Excellent range. Give it **Good** polish, and on GIA's system it can't be Excellent any more: the best it can get is Very Good. And symmetry is precise enough to measure in tenths of a degree. Try it in our Hearts & Arrows Scope. Tilt the [T73](https://digitalgemology.com/cuts/t73-round-brilliant)'s pavilion mains by at most a tenth of a degree, each a different amount. The symmetry of its hearts drops from 100% to 85%.\n\n![The same cut with Excellent and with Poor polish and symmetry.](https://digitalgemology.com/img/learn/gr-l5-t73-polish-symmetry-excellent-vs-poor.webp?v=d6e63746)\n\nThe same cut with Excellent and with Poor polish and symmetry.\n\n## Polish: the surface\n\n**Polish** describes how smooth the surface of the facets is, from **Excellent** to **Poor**. The grader looks at the stone at 10x for the marks that polishing or wear leaves:\n\n- tiny pits and nicks\n- fine polish lines\n- scratches\n- burn marks from overheating\n- rough patches.\n\nAt the low end, the stone's luster suffers even to the unaided eye.\n\n## Symmetry: the geometry\n\n**Symmetry**, also Excellent to Poor, is about geometry. Is the outline true? Does every facet have the right shape, sit in the right place and line up with its neighbors? GIA sorts the faults into two kinds:\n\n- **proportion faults**, such as an off-center table or culet, an out-of-round outline, a wavy girdle, or a table not parallel to the girdle;\n- **facet faults**, such as extra or missing facets, misshapen facets, facets that don't meet in a point, or crown and pavilion facets out of line with each other.\n\n## Why they matter: the cap\n\nOn a GIA report, polish and symmetry cap the cut grade of a round:\n\n| Polish and symmetry | Best possible cut grade |\n| --- | --- |\n| Excellent or Very Good | Excellent |\n| Good | Very Good |\n| Fair | Good |\n| Poor | Poor |\n\nGIA found that one grade of difference didn't noticeably change how observers rated a stone. That is why Very Good finish still allows Excellent.\n\n**On an IGI report:** IGI lists polish and symmetry for **every** shape and color. Low polish or symmetry can pull a round's cut grade down too. Its [\"Ideal\" comment](https://digitalgemology.com/learn/grading-reports/what-ideal-cut-means) needs at least Very Good for both.\n\n## Fluorescence: the glow\n\n**Fluorescence** is a glow. Shine ultraviolet light on some diamonds and they light up, usually blue, for as long as the UV is on. A GIA report gives its **strength and color** under long-wave UV. Two things to know:\n\n- **\"None\" doesn't mean zero.** It covers everything from no visible reaction up to very faint.\n- **It isn't a grade.** It's there to help identify the stone, not to rank it.\n\nGIA reports that about 25 to 35% of the diamonds it sees fluoresce, and more than 95% of them glow blue. For most stones, GIA says, it makes no noticeable difference to their looks.\n\n**On an IGI report:** IGI also records strength and color when fluorescence is present. It puts the share of fluorescent diamonds at around 35%.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator), T73 in diamond, **Photo studio**. In the report, under **Additional grading information**, step **Polish** from Excellent to Poor, then **Symmetry**. Watch the stone each time.\n2. Set the lighting to **UV lamp** and step **Fluorescence** from None to Very strong. Then go back to Photo studio.\n3. Open [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool). Under **More proportions**, set **Polish** to Good, then Fair. Read the grade and the **Limited by** line.\n4. **Break the hearts.** Open [Hearts & Arrows Scope](https://digitalgemology.com/tools/hearts-and-arrows-scope) with the T73. Move **Crown twist**, then **Main angles**, a little at a time. How small an error drops the symmetry figure below 95%?\n\n## What the tools show\n\n**In the simulator,** poor polish makes the stone look hazy and flat. It lowers contrast and color, because a rough surface scatters light. Poor symmetry tilts each crown and pavilion facet by up to 2°, and the pattern loses its order. Fluorescence glows blue under the UV lamp and changes nothing in daylight. The simulator is a learning tool, not a lab report: its polish and symmetry are simple models.\n\n**In the Cut Grading Tool,** Good polish makes the T73 Very Good and Fair polish makes it Good. The tool spells out the reason.\n\n**In the Scope,** the symmetry figure falls fast. Main angles off by up to a tenth of a degree give 90% face up and 85% face down. A crown twisted by one degree gives 92% and 88%. That's how fine the symmetry a grader judges really is.\n\n## Key points\n\n- Polish is the smoothness of the surface. Symmetry is the exactness of the outline and the facets. Both run Excellent to Poor.\n- On a GIA round, Good polish or symmetry caps the cut grade at Very Good, Fair at Good, Poor at Poor.\n- IGI lists polish and symmetry for every shape and color. Low finish can pull its cut grade down too.\n- Fluorescence is the strength and color of the glow under long-wave UV. \"None\" means anything from no reaction to very faint.\n- Fluorescence identifies a stone. It isn't part of the color or clarity grade.\n\n**Go further:** [fluorescence under the UV lamp](https://digitalgemology.com/learn/four-cs/fancy-color-diamonds-and-fluorescence), and [the cut grade's other limits](https://digitalgemology.com/learn/four-cs/how-diamond-cut-grade-is-determined).\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n- [Hearts & Arrows Scope](https://digitalgemology.com/tools/hearts-and-arrows-scope): See the arrows face up and the hearts face down as you change the cut.\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/reading-a-grading-report/polish-symmetry-and-fluorescence)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: The clarity plot: how to read the inclusion map on a report](https://digitalgemology.com/learn/grading-reports/diamond-clarity-plot)\n- [Try another topic · Diamond anatomy and proportions: Star length and lower half length in a round brilliant](https://digitalgemology.com/learn/diamond-anatomy/star-length-and-lower-half-length)\n\n[Previous lesson](https://digitalgemology.com/learn/grading-reports/what-ideal-cut-means) · [How to read a diamond grading report: all lessons](https://digitalgemology.com/learn/grading-reports) · [All topics](https://digitalgemology.com/learn)"},{"id":"GR-L6","course":"Reading a grading report","lesson_number":6,"title":"The clarity plot: how to read the inclusion map on a report","url":"https://digitalgemology.com/learn/grading-reports/diamond-clarity-plot","path":"/learn/grading-reports/diamond-clarity-plot","markdown":"https://digitalgemology.com/learn/grading-reports/diamond-clarity-plot.md","summary":"How to read the diamond clarity plot on a report: symbols for type, position and size, the key to symbols, and why the Dossier has no plot.","queries":["diamond clarity plot","clarity characteristics symbols","inclusion map diamond"],"quiz":"https://digitalgemology.com/skool/quiz/reading-a-grading-report/the-clarity-plot","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[How to read a diamond grading report](https://digitalgemology.com/learn/grading-reports) · 3 min read\n\n# The clarity plot: how to read the inclusion map on a report\n\nA diamond clarity plot is the map on a full grading report: an outline of the stone with a symbol for each characteristic's type, position and approximate size. The key to symbols lists the kinds shown, and the Diamond Dossier gives a written list instead.\n\n## A map of one diamond\n\nTwo SI2 diamonds can share the same grade, the same weight and the same color. You can still tell them apart in seconds. Turn to the clarity plot. Each full Diamond Grading Report carries a small drawing of the stone. It marks every significant inclusion and blemish where it sits. No two stones have the same map.\n\nThat's why the clarity characteristics matter beyond the grade. Like birthmarks, they identify one particular diamond. And they help gemologists separate natural stones from synthetics and simulants.\n\n![An SI2 T73 face up, the view a plot is drawn from.](https://digitalgemology.com/img/learn/gr-l6-t73-si2-face-up.webp?v=5eea152c)\n\nAn SI2 T73 face up, the view a plot is drawn from.\n\n## What the plot shows\n\nOn a GIA Diamond Grading Report:\n\n- The **plotted diagram** is an outline drawing of the stone's shape and cutting style.\n- **Symbols** on it show each clarity characteristic: its **type**, its **position** and roughly its **size**.\n- The **key to symbols** lists the kinds of characteristic that appear on the plot. A laser drill hole, for example, shows up there.\n\nThe clarity grade itself rests on what the plot records: the **size, nature, number, position and relief** of the characteristics, seen at 10x. Graders find each characteristic, and at least two of them grade independently. Then they draw the characteristics onto an outline that matches the stone's own shape and facets.\n\n## Why the Dossier has no plot\n\nThe **Diamond Dossier** grades the same four Cs but leaves out the plotted diagram. Instead it lists, in words, the **most significant characteristics** behind the clarity grade, **up to four** of them. It also carries the report number laser-inscribed on the girdle, so you can still identify the stone.\n\n**On an IGI report:** the method is the same idea: clarity at 10x, judged on the visibility, size, number, location and nature of the characteristics. The gemologist works around the stone segment by segment (IGI calls it a wedge technique). The result is a map of the stone. It records what's there and helps to recognize the stone later.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator), [T73](https://digitalgemology.com/cuts/t73-round-brilliant) in diamond, **Photo studio**, **View** face up. Set **Clarity grade** to **SI2**.\n2. Don't scroll down yet. Find every characteristic you can in the stone. Turn it a little to catch the ones that hide. Sketch a circle for the crown and mark where each one sits.\n3. Now scroll to **Clarity characteristics** in the report: crown on the left, pavilion on the right. Compare with your sketch. Then read the **Comments** line.\n4. Step the clarity to **VVS1** and to **I3**, and watch the diagram fill and empty.\n5. Open **PDF report**: the plot is printed on the page, the way a lab report carries it.\n\n## What the simulator shows\n\n**The plot.** At SI2 the simulator plots five characteristics: crystals, pinpoints and a feather. Each one is on the crown or pavilion view where it sits. Its Comments line lists their types. At VVS1 there's a single pinpoint; at I3, eight characteristics.\n\n**Your sketch.** Most people find some, not all. A few sit under facets that only show them at an angle, and the small ones vanish in the pattern. That's why a grader examines the stone at 10x, from several sides, before plotting.\n\n**What the plot is for.** It records the evidence for the grade, and it fingerprints the stone. Two stones with the same grade will still have different maps.\n\nThe simulator draws its plot from its own 3D model and its fixed set of characteristics per grade. It's a learning tool, not a lab plot.\n\n## Key points\n\n- A full report's clarity plot shows each characteristic's type, position and approximate size on a diagram of the stone's shape.\n- The key to symbols lists the kinds of characteristics shown. Treatments like laser drill holes appear there.\n- The clarity grade rests on size, nature, number, position and relief at 10x.\n- The Diamond Dossier has no plot. It lists up to four of the most significant characteristics in words and carries an inscription.\n- A plot fingerprints a stone: two stones with the same grade have different maps.\n\n**Go further:** [each clarity grade, from Flawless to I3](https://digitalgemology.com/learn/four-cs/diamond-clarity-scale).\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/reading-a-grading-report/the-clarity-plot)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: How to read the proportion diagram on a diamond report](https://digitalgemology.com/learn/grading-reports/diamond-proportion-diagram)\n- [Try another topic · The four Cs of diamonds: Carat weight vs size: why a 2 ct diamond isn't twice as big](https://digitalgemology.com/learn/four-cs/carat-weight-vs-size)\n\n[Previous lesson](https://digitalgemology.com/learn/grading-reports/polish-symmetry-and-fluorescence) · [How to read a diamond grading report: all lessons](https://digitalgemology.com/learn/grading-reports) · [All topics](https://digitalgemology.com/learn)"},{"id":"GR-L7","course":"Reading a grading report","lesson_number":7,"title":"How to read the proportion diagram on a diamond report","url":"https://digitalgemology.com/learn/grading-reports/diamond-proportion-diagram","path":"/learn/grading-reports/diamond-proportion-diagram","markdown":"https://digitalgemology.com/learn/grading-reports/diamond-proportion-diagram.md","summary":"How to read the proportion diagram on a diamond report: every number on the profile, and how to rebuild the stone and its cut grade from them.","queries":["diamond proportion diagram","gia proportions diagram","diamond report proportions"],"quiz":"https://digitalgemology.com/skool/quiz/reading-a-grading-report/the-proportion-diagram","tools":["https://digitalgemology.com/tools/cut-grading-tool"],"cuts":[],"text":"[How to read a diamond grading report](https://digitalgemology.com/learn/grading-reports) · 3 min read\n\n# How to read the proportion diagram on a diamond report\n\nThe proportion diagram on a diamond report is a side-view profile of the stone, drawn to its measured proportions: table, total depth, crown angle and height, pavilion angle and depth, star and lower half lengths, girdle and culet. GIA designed its cut grade so you can predict it from them.\n\nVideo: [How to read the proportion diagram on a diamond grading report (animated)](https://www.youtube.com/watch?v=CTBi2R9bVAg)\n\nEach number on the proportion diagram lands on the part of the stone that it measures. Crown height, girdle and pavilion depth add up to the total depth. Then the girdle and culet fix, live, from Very Good to Excellent. · 1 min 25 s · No sound, captions on screen\n\n## Transcript\n\nA GIA report has a small side view of the stone, with numbers around it.\n\nIt is a map. Each number measures one part of the stone.\n\nEvery percentage is a share of the average diameter.\n\nTable size: the width of the table, 53% of the diameter.\n\nCrown angle: the slope of the crown, 34.5°.\n\nCrown height: from the girdle up to the table, about 16.0%.\n\nGirdle: a description from thinnest to thickest, and a percentage.\n\nPavilion angle: the slope of the pavilion, 40.8°.\n\nPavilion depth: from the girdle down to the culet, about 43.0%.\n\nCulet size: the tip of the pavilion, as a word such as None or Medium.\n\nStar length: the stars reach 55% of the way from the table to the girdle.\n\nLower half length: the lower halves reach 80% of the way to the culet.\n\nThe three heights add up to the total depth: about 63.6%.\n\nThe parts are rounded, so the sum is approximate.\n\nAn optical device measures the stone without touching it.\n\nOn an IGI report, a 3D optical scan measures the stone.\n\nThe report prints the key measurements.\n\nIn our Cut Grading Tool, this stone is Very Good, for two reasons.\n\nThe total depth, about 63.6%, is past the Excellent limit of 63.0%.\n\nAnd the Medium culet caps the grade at Very Good on its own.\n\nThe one-number fix: what is the smallest change that makes it Excellent?\n\nThin the girdle to 3.5%. The depth falls to about 62.6%.\n\nBut the Medium culet still holds the stone at Very Good.\n\nMake the culet Small as well, and it is Excellent.\n\nNo single change does it. The angles were never the problem.\n\n## Everything you need is in the drawing\n\nIn the corner of a GIA report sits a small side-view drawing of the stone with numbers around it. It looks like decoration. It's the opposite.\n\nGIA designed its cut grading so that diamonds with the same rounded proportions, and the same girdle and culet descriptions, get the same grade. So the little drawing carries nearly everything the cut grade depends on. Copy its numbers into our Cut Grading Tool, and you can watch the grade appear. The tool also shows the reason a stone didn't make Excellent.\n\n![A report's proportions rebuilt in the Cut Grading Tool, its profile and grade.](https://digitalgemology.com/img/learn/gr-l7-cgt-stone-b.webp?v=bf216757)\n\nA report's proportions rebuilt in the Cut Grading Tool, its profile and grade.\n\n## What's on the diagram\n\nThe proportion diagram is a profile of the stone, drawn to its own measured proportions. GIA's diagram shows:\n\n- **table size** and **total depth**, as percentages of the average diameter;\n- **crown angle** and **crown height**;\n- **pavilion angle** and **pavilion depth**;\n- **star length** and **lower half length**;\n- **girdle thickness**, as a description from thinnest to thickest (such as \"Thin to Medium\") with a percentage, and whether it's faceted, polished or bruted;\n- **culet size**, as a description (None, Very Small and so on).\n\nAn optical device measures the stone without touching it. The report gives the numbers in rounded steps.\n\n**On an IGI report:** a 3D optical scan measures the stone, and the report prints the key measurements. Reports can include a graphic of the proportions too.\n\n## Rebuilding a stone\n\nOur Cut Grading Tool takes exactly these numbers. It rounds each one to the steps a report uses:\n\n- table 1%\n- crown 0.5°\n- pavilion 0.2°\n- star and lower half 5%\n- girdle 0.5%.\n\nThen it reads the grade from GIA's published tables. It draws the same kind of profile, so you can compare it with the report's. It's an educational estimate, not a GIA grade.\n\n### Try it yourself\n\n1. Open [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool). Enter this stone, adapted from one of GIA's worked examples. Table 53%, crown 34.5°, pavilion 40.8°, star 55%, lower half 80%, girdle 4.5% (Slightly Thick), culet Medium. (Open **More proportions** for the last four.)\n2. Read the grade and the **Limited by** line. Compare the **Profile** with the numbers you entered.\n3. **The one-number fix:** what's the smallest change that makes this stone Excellent? Is one change enough?\n4. Find a real report or listing with its proportion diagram (any round). Rebuild it the same way, and compare the tool's grade with the report's.\n\n## What the Cut Grading Tool shows\n\n**The grade.** In the tool, this stone comes out **Very Good**, for two reasons. The total depth, about 63.6%, is past the Excellent limit of 63.0%. And the Medium culet caps the grade at Very Good on its own. GIA's own version of this example prints a Slightly Thick to Thick girdle and a 64.2% total depth. It lists three limits: depth, girdle and culet. Our tool calculates the depth from the angles, so its figure differs.\n\n**The fix, in the tool.** No single change does it. Thin the girdle to 3.5% and the tool's depth falls to about 62.6%. But the Medium culet still holds the stone at Very Good. Make the culet Small as well, and it's Excellent. (With GIA's printed 64.2%, a 1% thinner girdle would still leave the depth just over 63%.) The angles were never the problem.\n\n**Reading it the other way.** Our pages on [diamond anatomy and proportions](https://digitalgemology.com/learn/diamond-anatomy) show how the numbers interact, one by one. Once you know that, the diagram tells you a lot at a glance:\n\n- A deep total depth with a thick girdle means weight below the face.\n- A pavilion near the edge of its range means the light return is at stake.\n\n## Key points\n\n- The proportion diagram is a profile of the stone drawn to its measured proportions.\n- It shows table, total depth, crown angle and height, pavilion angle and depth, star and lower half lengths, girdle and culet.\n- An optical device measures the proportions, and the report gives them in rounded steps.\n- GIA designed its cut grade so that you can predict it from those rounded numbers and descriptions.\n- Our Cut Grading Tool rebuilds a round from its diagram and estimates the grade, with the reason it stopped where it did.\n\n**Go further:** [every number on the diagram, one page each](https://digitalgemology.com/learn/diamond-anatomy), and [how to decode a whole stone from its numbers](https://digitalgemology.com/learn/diamond-anatomy/how-to-read-diamond-proportions).\n\n## Try it free\n\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/reading-a-grading-report/the-proportion-diagram)\n\n## Keep exploring\n\n- [Next lesson: Comments, treatments and lab-grown origin on a diamond report](https://digitalgemology.com/learn/grading-reports/diamond-report-comments-treatments-origin)\n- [Try another topic · Diamond anatomy and proportions: The parts of a diamond: crown, girdle and pavilion](https://digitalgemology.com/learn/diamond-anatomy/parts-of-a-diamond)\n\n[Previous lesson](https://digitalgemology.com/learn/grading-reports/diamond-clarity-plot) · [How to read a diamond grading report: all lessons](https://digitalgemology.com/learn/grading-reports) · [All topics](https://digitalgemology.com/learn)"},{"id":"GR-L8","course":"Reading a grading report","lesson_number":8,"title":"Comments, treatments and lab-grown origin on a diamond report","url":"https://digitalgemology.com/learn/grading-reports/diamond-report-comments-treatments-origin","path":"/learn/grading-reports/diamond-report-comments-treatments-origin","markdown":"https://digitalgemology.com/learn/grading-reports/diamond-report-comments-treatments-origin.md","summary":"How a lab-grown diamond report differs, where a report discloses treatments, and which treated stones get no grading report at all.","queries":["lab grown diamond report","diamond report comments","treated diamond report"],"quiz":"https://digitalgemology.com/skool/quiz/reading-a-grading-report/comments-treatments-and-origin","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[How to read a diamond grading report](https://digitalgemology.com/learn/grading-reports) · 4 min read\n\n# Comments, treatments and lab-grown origin on a diamond report\n\nA lab-grown diamond gets its own document: since 1 October 2025, GIA rates it Premium or Standard instead of D to Z, and IGI inscribes every lab-grown stone with \"LG\" before the report number. Detected treatments go in Comments, and unstable ones get an Identification Report instead.\n\n## Twins with different birth certificates\n\nTwo diamonds turn side by side. Same cut, same weight, D, Flawless. One formed deep in the earth. The other was grown in a laboratory. Which is which?\n\nYou can't tell, and neither can most jewelers by eye. Chemically and physically, a laboratory-grown diamond is a diamond: same carbon, same crystal, same way of handling light. Only a gem lab's instruments can tell the two apart. In our simulator the two render identically, pixel for pixel. Only one line on the report differs.\n\nThat's why the bottom of a report matters as much as the grades: the comments, the inscriptions and the report's own type.\n\n![The same stone as natural and as laboratory-grown.](https://digitalgemology.com/img/learn/gr-l8-natural-vs-lab-grown.webp?v=58a5d20f)\n\nThe same stone as natural and as laboratory-grown.\n\n## Comments: what doesn't fit elsewhere\n\n**Comments** hold any identifying characteristic or feature that has no other line on the report. Comments is also where a lab describes a **treatment** it has detected. If a color grade carries an [asterisk](https://digitalgemology.com/learn/grading-reports/diamond-report-grades), Comments explains it.\n\n## Treatments: graded, or not graded at all\n\nSome diamonds are treated to improve their color or apparent clarity. Anyone who sells a treated gem must disclose the treatment. GIA sorts treatments by whether they last:\n\n- **HPHT** (heating at high temperature under high pressure) can remove or change a diamond's color. GIA grades such a stone on a full grading report, not a Dossier: GIA doesn't issue a Dossier for HPHT-processed stones. GIA marks the color grade with an asterisk, explains it in Comments, and inscribes the girdle TREATED COLOR.\n- **Laser drilling** bores a tiny channel to an inclusion, usually a small dark one. The channel lets the laser burn the inclusion away, or lets a bleaching agent in. GIA grades the stone, shows the drill hole in the key to symbols and describes the treatment in Comments.\n- **Coating** (a very thin layer that masks the body color) and **fracture filling** (a glass-like filler injected into a crack) are **unstable**. GIA issues no grading report for them. It issues an **Identification Report** instead.\n\n## Origin: a report of its own\n\nPeople grow a lab-grown diamond with machines; the earth doesn't form it. The usual methods are **HPHT** or **CVD** (chemical vapor deposition). Yes, HPHT appears twice: the same high pressure and temperature can grow a diamond, or treat a natural one.\n\nSince 1 October 2025, GIA no longer grades lab-grown diamonds on the D-to-Z scale. Its **Laboratory-Grown Diamond Quality Assessment** rates a colorless to near-colorless lab-grown diamond **Premium** or **Standard**. Before that, GIA's digital **Laboratory-Grown Diamond Report** gave color and clarity grades. GIA inscribes a lab-grown stone with its number and **LABORATORY-GROWN**.\n\nSimulants such as glass or cubic zirconia aren't diamond at all. GIA doesn't grade them. It identifies them, on an Identification Report.\n\n**On an IGI report:** every lab-grown diamond IGI reports is inscribed with **\"LG\"** before the report number, and Comments notes the inscription. On request, IGI also notes the **growth method** (HPHT or CVD) and any treatment in Comments. IGI discloses permanent treatments in Comments. For non-permanent ones, IGI issues no full grading report.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator), [T73](https://digitalgemology.com/cuts/t73-round-brilliant) in diamond. In the report's **Additional grading information**, switch **Origin** from **Natural** to **Laboratory-grown**. What changes in the stone? On the report?\n2. Change **Gemstone** to moissanite. What does the Origin line say now, and why?\n3. **Sort the treatments.** For each one, say what GIA would issue: a grading report (and where the treatment would show), or an Identification Report. (a) HPHT color treatment, (b) laser drilling, (c) coating, (d) fracture filling.\n\n## What the simulator shows, and what GIA issues\n\n**Origin.** Switching to Laboratory-grown changes one line: Origin. The stone doesn't change by a single pixel. A real lab-grown diamond is the same. The difference is in its growth history, which instruments read and the report records. (The simulator is a learning tool, not a lab report. It lets you \"grade\" moissanite, which GIA would only identify. It also gives a lab-grown diamond D-to-Z grades, which GIA stopped in 2025.)\n\n**Moissanite.** The Origin line reads Laboratory-grown and you can't change it: moissanite and cubic zirconia used as gems are made in a laboratory.\n\n**The treatments.**\n\n- (a) HPHT: graded on a full report, with an asterisk on the color, an explanation in Comments and TREATED COLOR inscribed.\n- (b) Laser drilling: graded, drill hole in the key to symbols, described in Comments.\n- (c) Coating and (d) fracture filling: unstable, so an Identification Report, not a grading report.\n\n## Key points\n\n- Comments hold features that have no other line on the report, and the description of any detected treatment.\n- Permanent treatments (HPHT color, laser drilling) are graded and disclosed. Unstable ones (coating, fracture filling) get an Identification Report instead.\n- Lab-grown diamonds are essentially identical to natural ones. Only a lab can tell. Since 1 October 2025, GIA rates them Premium or Standard, not D to Z.\n- GIA inscribes lab-grown stones with their number and LABORATORY-GROWN; IGI with \"LG\" before the report number.\n- Simulants such as CZ aren't graded, only identified.\n\n**Go further:** [how a lab and a loupe tell a simulant from a diamond](https://digitalgemology.com/learn/diamond-vs-moissanite).\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/reading-a-grading-report/comments-treatments-and-origin)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: How to read a diamond grading report, start to finish](https://digitalgemology.com/learn/grading-reports/how-to-read-a-diamond-grading-report)\n- [Try another topic · Diamond anatomy and proportions: Pavilion angle and pavilion depth: how a diamond keeps the light in](https://digitalgemology.com/learn/diamond-anatomy/diamond-pavilion-angle)\n\n[Previous lesson](https://digitalgemology.com/learn/grading-reports/diamond-proportion-diagram) · [How to read a diamond grading report: all lessons](https://digitalgemology.com/learn/grading-reports) · [All topics](https://digitalgemology.com/learn)"},{"id":"GR-L9","course":"Reading a grading report","lesson_number":9,"title":"How to read a diamond grading report, start to finish","url":"https://digitalgemology.com/learn/grading-reports/how-to-read-a-diamond-grading-report","path":"/learn/grading-reports/how-to-read-a-diamond-grading-report","markdown":"https://digitalgemology.com/learn/grading-reports/how-to-read-a-diamond-grading-report.md","summary":"How to read a diamond grading report, start to finish: a six-step checklist, the IGI differences side by side, and a practice sheet with five errors.","queries":["how to read a diamond grading report","how to read a gia certificate","diamond report example"],"quiz":"https://digitalgemology.com/skool/quiz/reading-a-grading-report/read-a-whole-report","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator","https://digitalgemology.com/tools/cut-grading-tool"],"cuts":[],"text":"[How to read a diamond grading report](https://digitalgemology.com/learn/grading-reports) · 4 min read\n\n# How to read a diamond grading report, start to finish\n\nRead every diamond report in the same order: report type, identity, grades, finish, diagrams and fine print. At each step, check that the fields agree: the measurements with the total depth, the polish and symmetry with the cut grade, and every asterisk with Comments.\n\n## Five things wrong with this report\n\nBelow is a made-up practice sheet. It looks like the main fields of a GIA Diamond Dossier. It contains **five errors**: five things that can't be true together on a real report. By the end of this page you'll find them all.\n\n| Field | Practice sheet (not a real report) |\n| --- | --- |\n| Report type | Diamond Dossier |\n| Shape and cutting style | Round Brilliant |\n| Measurements | 6.10 – 6.14 × 3.81 mm |\n| Carat weight | 0.90 carat |\n| Color grade | H* |\n| Clarity grade | VS2 |\n| Cut grade | Excellent |\n| Polish | Good |\n| Symmetry | Excellent |\n| Fluorescence | None |\n| Inscription(s) | None |\n| Comments | None |\n| Total depth | 60.0% |\n| Clarity | plotted diagram with key to symbols |\n\n## The checklist\n\nRead every report in the same order. Each step has its own page:\n\n1. **What kind of report is it?** Diamond Grading Report, Dossier, Laboratory-Grown Diamond Quality Assessment (or an older Laboratory-Grown Diamond Report) or Identification Report? Each has its own scope (see [the report types](https://digitalgemology.com/learn/grading-reports/what-is-a-diamond-grading-report)).\n2. **Who is this stone?** Date, number, shape and cutting style, measurements. Do the measurements fit the carat weight? Do the inscription and the online record match (see [the ID section](https://digitalgemology.com/learn/grading-reports/diamond-report-identity-section))?\n3. **The grades.** Color (look for an asterisk), clarity, and a cut grade only where the lab gives one (see [the grades](https://digitalgemology.com/learn/grading-reports/diamond-report-grades)). If \"Ideal\" appears anywhere, which kind is it (see [what \"Ideal\" means](https://digitalgemology.com/learn/grading-reports/what-ideal-cut-means))?\n4. **The finish.** Polish and symmetry: do they allow the cut grade? Fluorescence: strength and color, not a grade (see [polish, symmetry and fluorescence](https://digitalgemology.com/learn/grading-reports/polish-symmetry-and-fluorescence)).\n5. **The diagrams.** A clarity plot on a full report, a written list on a Dossier (see [the clarity plot](https://digitalgemology.com/learn/grading-reports/diamond-clarity-plot)). The proportion diagram: does the total depth match the measurements (see [the proportion diagram](https://digitalgemology.com/learn/grading-reports/diamond-proportion-diagram))?\n6. **The fine print.** Comments, treatments, inscriptions, origin (see [comments, treatments and origin](https://digitalgemology.com/learn/grading-reports/diamond-report-comments-treatments-origin)).\n\n## The IGI differences, side by side\n\n|  | GIA | IGI |\n| --- | --- | --- |\n| Stones in jewelry | Diamond grading reports for loose stones | Also graded \"as mounting permits\": color and clarity as a range, estimated cut grade |\n| Inscription | Report number on the girdle; always on a Dossier | Laserscribe; every lab-grown stone gets \"LG\" plus the number; natural on request |\n| Balance | Reads to five decimals, reports two | Reads to four decimals, reports two |\n| Cut grade, rounds | Excellent to Poor; individual limits plus table, crown and pavilion judged in combination | Excellent to Poor; one published range per proportion per grade; fish-eye caps at Fair |\n| \"Ideal\" | Not a cut grade; AGS Ideal is a light performance supplement | A comment on an Excellent round inside a narrower band (\"Excellent-Ideal\") |\n| Cut grade, fancy shapes | None | Optional, Excellent to Poor; four checks to earn Excellent |\n| Lab-grown stones | Own report, digital, looks different | \"LG\" inscription noted in Comments; growth method on request |\n| Unstable treatments | Identification Report only | No full grading report |\n\n### Try it yourself\n\n1. Run the checklist on the practice sheet above. Write down every line that can't be right, and why.\n2. Then open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) and build a round like the one on the sheet: H, VS2. The simulator's carat steps don't include 0.90 ct, so use 1.00 ct. Compare its measurements line and total depth with the sheet's.\n3. Open the simulator's **PDF report** and run the same checklist on it.\n\n## What the checklist finds\n\nThe five errors:\n\n1. **The total depth.** The measurements give an average diameter of 6.12 mm, and 3.81 ÷ 6.12 is 62.3%, not 60.0%. The two numbers describe different stones.\n2. **The asterisk.** H* means a detected color treatment, and Comments must explain it. Comments says None. This line is a red flag twice over. A color-treated stone would also carry TREATED COLOR on its girdle. And GIA doesn't issue a Dossier for HPHT-processed stones at all.\n3. **The cut grade.** Good polish caps a GIA round at Very Good. Excellent can't stand next to it.\n4. **The plot.** A Dossier has no plotted diagram. It lists up to four characteristics in words instead.\n5. **The inscription.** A Dossier always carries its report number laser-inscribed on the girdle. \"None\" can't be right.\n\nEverything else fits:\n\n- A 0.90 ct round falls inside the Dossier's weight range.\n- VS2 and H are ordinary grades.\n- Fluorescence \"None\" just means indiscernible to very faint.\n\nNone of these errors needed a loupe. A report checks itself, if you read it in order.\n\nWhen you practice on the simulator's PDF report, remember that it's a learning tool, not a lab report. It has a simulation number, not a report number, and nothing to verify online.\n\n## Key points\n\n- Read every report in the same order: type, identity, grades, finish, diagrams, fine print.\n- The measurements and the total depth must agree. So must the polish, symmetry and cut grade.\n- Every asterisk needs an explanation in Comments.\n- Each report type has its own scope: a Dossier has no plot but always an inscription.\n- IGI differs in a few clear places: mounted stones, inscriptions, cut grading, and what \"Ideal\" means.\n\n**Go further:** [take the quiz on reading a grading report](https://digitalgemology.com/skool/quiz/reading-a-grading-report).\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n- [Cut Grading Tool](https://digitalgemology.com/tools/cut-grading-tool): Grade a round brilliant from its proportions and see its light map change.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/reading-a-grading-report/read-a-whole-report)\n\n## Keep exploring\n\n- [Try another topic · The four Cs of diamonds: How a diamond cut grade is set: proportions, polish and symmetry](https://digitalgemology.com/learn/four-cs/how-diamond-cut-grade-is-determined)\n\n[Previous lesson](https://digitalgemology.com/learn/grading-reports/diamond-report-comments-treatments-origin) · [How to read a diamond grading report: all lessons](https://digitalgemology.com/learn/grading-reports) · [All topics](https://digitalgemology.com/learn)"},{"id":"DM-L1","course":"Diamond vs moissanite","lesson_number":1,"title":"Diamond vs moissanite: two look-alikes, two different materials","url":"https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-differences","path":"/learn/diamond-vs-moissanite/diamond-vs-moissanite-differences","markdown":"https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-differences.md","summary":"Diamond vs moissanite: carbon in a cubic crystal against silicon carbide in a hexagonal one. Why moissanite is a simulant, and why it is always lab-grown.","queries":["diamond vs moissanite","what is moissanite","moissanite vs diamond differences"],"quiz":"https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/two-look-alikes-two-materials","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Diamond vs moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite) · 3 min read\n\n# Diamond vs moissanite: two look-alikes, two different materials\n\nDiamond is carbon in a cubic crystal; moissanite is silicon carbide in a hexagonal one. So moissanite is a look-alike, a diamond simulant, and because natural moissanite crystals are tiny (the largest known is 4.1 mm), every moissanite in jewelry is laboratory-grown.\n\nVideo: [The T73 at 1.00 ct in diamond and in moissanite](https://www.youtube.com/watch?v=jMYuj1xYWSg)\n\nThe T73 at 1.00 ct in diamond and in moissanite, turning side by side in sunlight. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nThe T73 at 1.00 ct in diamond and in moissanite, turning side by side in sunlight.\n\n## Two round stones, side by side\n\nPut a diamond and a moissanite next to each other: same cut, same weight. Both are colorless, both sparkle, and at arm's length most people can't say which is which. (Look closely: the moissanite is a little wider. We explain why in [same size, different weight](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-carat-size).)\n\nBut they are not two versions of one thing. They are two different materials that look alike, as a red spinel can pass for a ruby. Everything that separates them starts here: the [fire](https://digitalgemology.com/learn/diamond-vs-moissanite/why-moissanite-has-more-fire), the [doubled facets](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test), the [weight](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-carat-size).\n\n## Two materials\n\n**Diamond** is a single element, carbon. Every atom holds on to four neighbors in a cubic network. Natural diamond is a deep-earth mineral. It forms under enormous heat and pressure about 160 km below our feet, and it only reaches the surface when an eruption carries it up. A **laboratory-grown diamond** is the same material, made by one of two methods: HPHT (high pressure, high temperature) or CVD (chemical vapor deposition). It has essentially the same composition, structure and properties. So it is diamond, just not from the ground.\n\n**Moissanite** is silicon carbide: one silicon atom for every carbon atom, stacked in layers with hexagonal symmetry. The chemistry is different, and the crystal system is different. So moissanite is a different material, and no moissanite is a diamond of any kind.\n\n## Three boxes\n\nEvery colorless stone sold as, or next to, a diamond fits in one of three boxes:\n\n1. **Natural diamond.**\n2. **Laboratory-grown diamond.** Still diamond.\n3. **Simulant**: a look-alike that isn't diamond at all. GIA names cubic zirconia as the most common simulant today, and moissanite as the next.\n\nMoissanite goes in box 3. Be careful with one word that does two jobs. A \"lab-grown moissanite\" and a \"lab-grown diamond\" are both made in a lab, but only one of them is diamond. A simulant is a different material, so it gives itself away somewhere: in how it handles light, in its weight, or in how it reacts to an instrument. Our other pages on [diamond vs moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite) show which tests catch it and which tests don't.\n\n## Natural moissanite is real, but not in your ring\n\nThe mineral is named after the French chemist Henri Moissan. He found natural silicon carbide in the Canyon Diablo meteorite in Arizona. In 1905 the mineral got the name moissanite, in his honor.\n\nOn Earth it is very rare, and the crystals are tiny: usually under 1.5 mm. The largest known crystal comes from the Kishon River area in northern Israel. It measures 4.1 mm, and those crystals are blue to light green. No one cuts colorless jewelry stones from that.\n\nSo every faceted moissanite you will meet was grown in a laboratory. Its producer planned to release near-colorless moissanite to jewelers in early 1998. That was just after GIA published its first full study of the material, in the winter of 1997.\n\n![The diamond and moissanite crystal models from the two gemstone pages, side by side.](https://digitalgemology.com/img/learn/dm-l1-crystal-models.webp?v=7fcc7764)\n\nThe diamond and moissanite crystal models from the two gemstone pages, side by side.\n\n### Try it yourself\n\n1. Open the [diamond gemstone page](https://digitalgemology.com/gemstones/diamond) and drag the crystal model at the top. You see one kind of atom, in a cubic cell.\n2. Open the [moissanite gemstone page](https://digitalgemology.com/gemstones/moissanite) and turn its model. You see two kinds of atom, silicon and carbon, in hexagonal layers. The model shows 6H, the form that gem moissanite is made of. Its stack of layers repeats every six layers.\n3. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the [T73 Round Brilliant](https://digitalgemology.com/cuts/t73-round-brilliant) in diamond. In the report, find **Origin**. You can set it to Natural or Laboratory-grown.\n4. Change the gemstone to moissanite. What happens to the Origin row?\n\n## What the simulator shows\n\nFor diamond, the Origin row is a choice. The same material can come from the earth or from a lab, and a report has to say which. For moissanite, the row locks to **Laboratory-grown**, because gem moissanite doesn't come out of the ground. So before anyone looks at the sparkle, the two stones already differ: in what they are made of, in how their atoms are arranged, and in where they can come from.\n\n## Key points\n\n- Diamond is carbon in a cubic crystal; moissanite is silicon carbide in a hexagonal one.\n- A laboratory-grown diamond is diamond. Moissanite is a different material, so it is a diamond simulant.\n- Natural moissanite occurs only as tiny crystals (the largest known is 4.1 mm), so moissanite in jewelry is laboratory-grown.\n- The two are different materials, so standard gem tests can separate them. But not every test can.\n\n**Go further:** the [diamond](https://digitalgemology.com/gemstones/diamond) and [moissanite](https://digitalgemology.com/gemstones/moissanite) gemstone pages list every property that we compare in [diamond vs moissanite properties](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-properties).\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/two-look-alikes-two-materials)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Diamond vs moissanite properties: hardness, refractive index, dispersion, density](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-properties)\n- [Try another topic · How to read a diamond grading report: How to read the proportion diagram on a diamond report](https://digitalgemology.com/learn/grading-reports/diamond-proportion-diagram)\n\n[Diamond vs moissanite: all lessons](https://digitalgemology.com/learn/diamond-vs-moissanite) · [All topics](https://digitalgemology.com/learn)"},{"id":"DM-L2","course":"Diamond vs moissanite","lesson_number":2,"title":"Diamond vs moissanite properties: hardness, refractive index, dispersion, density","url":"https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-properties","path":"/learn/diamond-vs-moissanite/diamond-vs-moissanite-properties","markdown":"https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-properties.md","summary":"Moissanite vs diamond hardness (Mohs 9.25 vs 10), refractive index, dispersion and specific gravity side by side, and what each number predicts.","queries":["moissanite vs diamond hardness","moissanite refractive index vs diamond","moissanite density"],"quiz":"https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/the-property-card","tools":["https://digitalgemology.com/tools/refractometer","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Diamond vs moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite) · 4 min read\n\n# Diamond vs moissanite properties: hardness, refractive index, dispersion, density\n\nDiamond is harder, Mohs 10 against 9.25 for moissanite, but it has cleavage, and moissanite showed none. Moissanite also differs in refractive index (2.648 to 2.691 against 2.417), dispersion (0.104 against 0.044) and specific gravity (3.22 against 3.52).\n\n## Different materials, different numbers\n\nDiamond and moissanite are [two different materials](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-differences): carbon in a cubic crystal against silicon carbide in a hexagonal one. A different material behaves differently with light, weight and wear. Gemologists record that behavior as a short list of numbers.\n\nYou don't need to memorize the list. You need to know what each line predicts. Every test that separates the two stones is one of these numbers, turned into something you can see.\n\n## The card\n\n| Property | Diamond | Moissanite | What it predicts | More on it |\n| --- | --- | --- | --- | --- |\n| Refractive index | 2.417 | 2.648 to 2.691 | How strongly the stone bends light | [refractive index](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-refractive-index-and-cut), [instruments](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite) |\n| Critical angle | 24.4° | 22.2° | Which light stays inside the stone | [refractive index](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-refractive-index-and-cut) |\n| Optic character | singly refractive | doubly refractive (uniaxial positive) | Whether light splits in two | [loupe test](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test), [instruments](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite) |\n| Birefringence | none | 0.043 | How far the two rays split | [loupe test](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test) |\n| Dispersion | 0.044 | 0.104 | How much white light spreads into colors (fire) | [fire](https://digitalgemology.com/learn/diamond-vs-moissanite/why-moissanite-has-more-fire) |\n| Specific gravity | 3.52 | 3.22 | Weight for its size | [carat and size](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-carat-size) |\n| Mohs hardness | 10 | 9.25 | Resistance to scratching | [wear and care](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-durability-and-care) |\n| Toughness | good along its cleavage directions, exceptional in others | excellent; no cleavage found | Resistance to chipping and breaking | [wear and care](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-durability-and-care) |\n| Luster | adamantine | subadamantine | How the surface reflects | – |\n| Heat conduction | very high | close to diamond's | What a thermal tester says | [testers](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite) |\n\n![The simulator's report for diamond and for moissanite, with the rows that change outlined.](https://digitalgemology.com/img/learn/dm-l2-report-rows-diamond-vs-moissanite.webp?v=87d0ac40)\n\nThe simulator's report for diamond and for moissanite, with the rows that change outlined.\n\n## Reading the lines\n\n**Refractive index** is how much light slows down and bends when it enters the stone. Moissanite has two indices, one for each of the two rays it splits light into. The gap between them is its **birefringence**, 0.043. Diamond has a single index, so it has no gap.\n\n**Critical angle** comes from the index. Inside the stone, light that meets a facet at more than this angle from the facet's perpendicular reflects back in. A higher index gives a smaller critical angle. That is why moissanite's critical angle is smaller than diamond's.\n\n**Dispersion** is how differently the stone bends red and violet light. It is measured as the difference in index between a red and a violet line of the spectrum (686.7 and 430.8 nm). Moissanite's figure is about 2.4 times diamond's.\n\n**Specific gravity** compares the stone's weight with the weight of the same volume of water. Diamond is 3.52 times as heavy, moissanite 3.22 times.\n\n**Hardness and toughness** are two different things. Hardness is resistance to scratching. Toughness is resistance to chipping and breaking. Diamond is the hardest gem, but it has cleavage: directions along which a hard knock can split it. GIA's researchers smashed a moissanite cube with a hammer. It broke with curved, shell-like fractures and showed no cleavage.\n\nOne warning about **Mohs**: it is a ranking, not a ruler. In measured indentation hardness, the jump from sapphire (9) to moissanite (9.25) is larger than the whole step from topaz (8) to sapphire. And diamond, at 10, is far harder than either.\n\n**Heat conduction** is the odd one out. Here the two are so close that the classic thermal diamond tester can't separate them. Our page on [diamond testers and moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite) shows what to use instead.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the [T73 Round Brilliant](https://digitalgemology.com/cuts/t73-round-brilliant) in diamond, 1.00 carat.\n2. Scroll the report to **Additional grading information**. Note the refractive index, dispersion, birefringence and hardness.\n3. Scroll down to **Light performance** and note the critical angle.\n4. Change the gemstone to moissanite. Write down every row that changes.\n5. Look for the row that disappears. Also look for one number at the top of the report that changed, although you didn't touch it.\n\n## What the simulator report shows\n\nFive property rows changed: refractive index, dispersion, birefringence, hardness and critical angle. The **Origin** row locked to Laboratory-grown (see [what the two stones are made of](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-differences)). The **Fluorescence** row disappeared, because in the simulator only diamond is graded for it (see [color and fluorescence](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-color-and-fluorescence)). The Light Return bar shifted too; [moissanite's refractive index](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-refractive-index-and-cut) explains why. And the **Measurements** at the top grew from 6.48 to 6.67 mm across, at the same 1.00 carat. That's specific gravity at work: see [same size, different weight](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-carat-size).\n\nEverything else on the card turns into something you can see:\n\n- the index turns into [the way a cut returns light](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-refractive-index-and-cut);\n- dispersion turns into [fire](https://digitalgemology.com/learn/diamond-vs-moissanite/why-moissanite-has-more-fire);\n- birefringence turns into [doubled facet edges](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test).\n\n## Key points\n\n- Diamond's index is 2.417. Moissanite's is 2.648 to 2.691: two indices, because it is doubly refractive.\n- Moissanite's dispersion, 0.104, is about 2.4 times diamond's 0.044.\n- Moissanite is lighter for its size: specific gravity 3.22 against 3.52.\n- Diamond is harder (Mohs 10 against 9.25) but has cleavage. Moissanite showed none.\n- Their heat conduction is so close that a thermal tester calls both \"diamond\".\n\n**Go further:** our [gemstone constants](https://digitalgemology.com/about/how-we-measure/gemstone-constants) page lists the same numbers for all seven gemstones. It also shows how we calculate each angle.\n\n## Try it free\n\n- [Refractometer](https://digitalgemology.com/tools/refractometer): Read the shadow edges of seven gemstones on a gem refractometer.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/the-property-card)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Moissanite's refractive index, and why it needs its own cut](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-refractive-index-and-cut)\n- [Try another topic · The four Cs of diamonds: Carat weight vs size: why a 2 ct diamond isn't twice as big](https://digitalgemology.com/learn/four-cs/carat-weight-vs-size)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-differences) · [Diamond vs moissanite: all lessons](https://digitalgemology.com/learn/diamond-vs-moissanite) · [All topics](https://digitalgemology.com/learn)"},{"id":"DM-L3","course":"Diamond vs moissanite","lesson_number":3,"title":"Moissanite's refractive index, and why it needs its own cut","url":"https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-refractive-index-and-cut","path":"/learn/diamond-vs-moissanite/moissanite-refractive-index-and-cut","markdown":"https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-refractive-index-and-cut.md","summary":"Moissanite's refractive index (2.648 to 2.691) bends light more than diamond's 2.417. Why diamond-cut moissanite loses its hearts and arrows.","queries":["moissanite refractive index","best cut for moissanite","moissanite hearts and arrows"],"quiz":"https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/refractive-index-why-dg-anteros-exists","tools":["https://digitalgemology.com/tools/hearts-and-arrows-scope","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/dg-anteros","https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Diamond vs moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite) · 5 min read\n\n# Moissanite's refractive index, and why it needs its own cut\n\nMoissanite's refractive index is 2.648 to 2.691, against diamond's 2.417, so it bends every ray further. Diamond angles such as the T73's lose their hearts and arrows in moissanite; DG-Anteros re-solves the crown and pavilion for moissanite's index and brings them back.\n\nVideo: [The T73 and DG-Anteros, both in moissanite, turning side by side](https://www.youtube.com/watch?v=FoIm03eunds)\n\nThe T73 and DG-Anteros, both in moissanite, turning side by side. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nThe T73 and DG-Anteros, both in moissanite, turning side by side.\n\n## A pattern that vanishes\n\nHere's a trick to start with. Open a Hearts & Arrows viewer on a perfectly cut round brilliant in diamond: eight crisp arrows face-up, eight hearts face-down. Now change nothing about the cut. Not one facet, not one angle. Only change the stone, from diamond to moissanite.\n\nBoth patterns fall apart.\n\nThe cause is the first number on the [property card](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-properties): the refractive index. This page is about that one number, and about the cut we drew because of it.\n\n## What refractive index is\n\nLight slows down when it enters a stone. The refractive index (RI) tells you how much. It is the speed of light in air (strictly, in a vacuum) divided by its speed in the stone.\n\n- In **diamond** (RI 2.417), light crawls along at about 124,000 km per second.\n- In **moissanite** (RI 2.648, and 2.691 for its second ray), it's down to about 113,000 km per second.\n\nSlower light bends more where it crosses a surface at an angle. So moissanite bends every ray that enters or leaves it further than diamond does. (Its second index has its own effect: it [doubles the facet edges](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test).)\n\nTwo things follow:\n\n1. **Off the scale.** A gem refractometer reads only up to about 1.81, the index of its contact liquid. Both stones are far beyond the end of the scale and read \"over the limit\". So the standard instrument can't read the most important number on this page.\n2. **A tighter trap.** Inside a stone, light can escape through a facet only near straight-on. The limit is the critical angle. Beyond that angle, the facet is a perfect mirror. Diamond's critical angle is 24.4°; moissanite's is 22.2°. Moissanite's escape window is narrower, so it holds light more easily.\n\n## Why a diamond cut misfires in moissanite\n\nA round brilliant is a light machine. Light comes in through the top, bounces off the pavilion and comes back up toward your eye. The crown and pavilion angles are set to make that happen. The [T73](https://digitalgemology.com/cuts/t73-round-brilliant)'s angles go back to 1919, and they were worked out for diamond's index, 2.417.\n\nPut those same angles in moissanite, and every ray bends a little further. It meets the pavilion at a different angle and leaves at a slightly different place. The stone still holds light, but it doesn't send the light where the design intended. Most moissanite is cut to diamond proportions like this.\n\nThat's why we drew **[DG-Anteros](https://digitalgemology.com/cuts/dg-anteros)**: the T73's 73-facet layout, with the crown and pavilion re-solved for moissanite's index.\n\nVideo: [The T73 in diamond through the H&A viewer](https://www.youtube.com/watch?v=WP4JPFvj_QA)\n\nThe T73 in diamond through the H&A viewer, eight arrows turning over into eight hearts. · 10 s · No sound\n\n![The same cut in moissanite: both patterns gone, symmetry still 100%.](https://digitalgemology.com/img/learn/dm-l3-t73-moissanite-hearts-arrows.webp?v=ee7f96d5)\n\nThe same cut in moissanite: both patterns gone, symmetry still 100%.\n\n### Try it yourself\n\n1. Open [Hearts & Arrows Scope](https://digitalgemology.com/tools/hearts-and-arrows-scope). It starts with the T73 in diamond. Set the gemstone to **Moissanite** and watch both patterns go.\n2. Look at the two **Symmetry** readings. Still 100%?\n3. Set the cut to **DG-Anteros**, still in moissanite. Note its pavilion and crown angles in the panel.\n4. Switch DG-Anteros to **Diamond**.\n5. **The rescue challenge.** Go back to the T73 in moissanite. Using only the **Pavilion angle** and **Crown angle** controls, bring the hearts and arrows back. Which angles work?\n6. In [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator), turn on **Light map**. Read the **Light Return** bar for the T73 in diamond, the T73 in moissanite, and DG-Anteros in moissanite.\n\n## What the scope and the light map show\n\nIn moissanite, the T73's arrows dissolve into a red field with scattered dark marks, and its hearts melt into a dark star. But symmetry stays at 100%: all sixteen halves still match each other. Symmetry makes a pattern even. The proportions, matched to the index, make the pattern exist.\n\nDG-Anteros has a pavilion of 40.1° and a crown of 33° in the scope; the T73 has 40.75° and 34.5°. In moissanite, DG-Anteros shows crisp white arrows and eight clean hearts. Switch it to diamond and the trick runs backwards: its arrows go dark and its hearts flood. **A cut is matched to its material, not better in general.**\n\nVideo: [DG-Anteros in moissanite, crisp arrows and eight clean hearts](https://www.youtube.com/watch?v=f2LSr3MRFOw)\n\nDG-Anteros in moissanite, crisp arrows and eight clean hearts. · 10 s · No sound\n\n![DG-Anteros in diamond: arrows dark, hearts flooded.](https://digitalgemology.com/img/learn/dm-l3-dg-anteros-diamond-hearts-arrows.webp?v=597f47da)\n\nDG-Anteros in diamond: arrows dark, hearts flooded.\n\nThe rescue works too. Set the T73 in moissanite to around 40.1° pavilion and 33° crown, and the arrows and hearts come back. Two sliders find the whole idea of DG-Anteros.\n\n![The T73 in moissanite at pavilion 40.1° and crown 33°: the hearts are back.](https://digitalgemology.com/img/learn/dm-l3-t73-moissanite-rescued-hearts-arrows.webp?v=58e08dba)\n\nThe T73 in moissanite at pavilion 40.1° and crown 33°: the hearts are back.\n\nThe light map shows what happens to the light itself. Light Return sorts the face-up stone by where its light comes from:\n\n- **direct**: bright light from above, 15° to 45° off your line of sight;\n- **indirect**: light from lower angles;\n- **contrast**: where your own head blocks the light;\n- **leakage**: light lost through the pavilion.\n\n| Stone | Direct | Indirect | Contrast | Leakage |\n| --- | --- | --- | --- | --- |\n| T73 in diamond | 69% | 5% | 22% | 4% |\n| T73 in moissanite | 49% | 28% | 11% | 12% |\n| DG-Anteros in moissanite | 61% | 13% | 24% | 2% |\n\n![The three light maps face up: T73 in diamond, T73 in moissanite, DG-Anteros in moissanite.](https://digitalgemology.com/img/learn/dm-l3-light-map-t73-diamond-moissanite-dg-anteros.webp?v=87d71a6d)\n\nThe three light maps face up: T73 in diamond, T73 in moissanite, DG-Anteros in moissanite.\n\nIn moissanite, the T73 swaps bright overhead light for low-angle light. It loses contrast, and it leaks more than twice as much. DG-Anteros brings back the direct light and the contrast, and it leaks least of all three. On the Cut Performance Wheel, it lifts brilliance in moissanite from the T73's 86 to 92.\n\n## Key points\n\n- Refractive index is how much a stone slows light: diamond 2.417, moissanite about 2.65. A higher index bends light more.\n- Both stones are beyond a refractometer's scale and read \"over the limit\".\n- Moissanite's critical angle (22.2°) is smaller than diamond's (24.4°), so it traps light more easily.\n- A cut's angles are solved for one index. The T73 loses its hearts and arrows in moissanite, but its symmetry stays 100%.\n- DG-Anteros re-solves the T73 for moissanite: crisp hearts and arrows, more direct light, less leakage. In diamond it misfires. A cut is matched to its material.\n\n**Go further:** the [DG-Anteros cut page](https://digitalgemology.com/cuts/dg-anteros) shows the cut in both stones. It also has the cutting files and 3D models.\n\n## Try it free\n\n- [Hearts & Arrows Scope](https://digitalgemology.com/tools/hearts-and-arrows-scope): See the arrows face up and the hearts face down as you change the cut.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/refractive-index-why-dg-anteros-exists)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [DG-Anteros Cut](https://digitalgemology.com/cuts/dg-anteros): 3D files and cutting files, €9.99 each\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Why moissanite shows more fire than diamond](https://digitalgemology.com/learn/diamond-vs-moissanite/why-moissanite-has-more-fire)\n- [Try another topic · Diamond anatomy and proportions: Star length and lower half length in a round brilliant](https://digitalgemology.com/learn/diamond-anatomy/star-length-and-lower-half-length)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-properties) · [Diamond vs moissanite: all lessons](https://digitalgemology.com/learn/diamond-vs-moissanite) · [All topics](https://digitalgemology.com/learn)"},{"id":"DM-L4","course":"Diamond vs moissanite","lesson_number":4,"title":"Why moissanite shows more fire than diamond","url":"https://digitalgemology.com/learn/diamond-vs-moissanite/why-moissanite-has-more-fire","path":"/learn/diamond-vs-moissanite/why-moissanite-has-more-fire","markdown":"https://digitalgemology.com/learn/diamond-vs-moissanite/why-moissanite-has-more-fire.md","summary":"Why moissanite has more fire than diamond: dispersion 0.104 against 0.044. The T73 scores 97 for fire in moissanite and 78 in diamond.","queries":["moissanite fire vs diamond","moissanite rainbow sparkle","dispersion diamond moissanite"],"quiz":"https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/fire-the-main-optical-difference","tools":["https://digitalgemology.com/tools/cut-performance-wheel","https://digitalgemology.com/tools/3d_gemstone_simulator","https://digitalgemology.com/tools/spectroscope"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant","https://digitalgemology.com/cuts/dg-m5"],"text":"[Diamond vs moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite) · 4 min read\n\n# Why moissanite shows more fire than diamond\n\nMoissanite shows more fire because its dispersion, 0.104, is about 2.4 times diamond's 0.044, so each facet fans white light into wider colors. In the same T73, moissanite scores 97 for fire against diamond's 78, and it out-fires diamond in 36 of the 37 cuts we score.\n\nVideo: [Why moissanite has more fire than diamond: dispersion explained (animated)](https://www.youtube.com/watch?v=fTZqBo1-a1s)\n\nRefractive index against wavelength for both stones: dispersion 0.044 in diamond and 0.104 in moissanite. One ray that leaves a crown facet fans into colors, 0.84° wide in diamond and 2.14° in moissanite. On the Cut Performance Wheel, the T73 scores fire 78 in diamond and 97 in moissanite. Moissanite is ahead in 36 of 37 cuts. · 1 min 29 s · No sound, captions on screen\n\n## Transcript\n\nWhite light is a mix of colors. The index is higher for violet than for red.\n\nDispersion is the index at 430.8 nm minus the index at 686.7 nm.\n\nDiamond: 0.044. Moissanite: 0.104, about 2.4 times as much.\n\nLight leaves a cut stone through its top facets. Look at one crown facet.\n\nClose up: one ray of white light meets the facet at 15.0° inside.\n\nSnell's law gives the angle outside. Each color has its own index n.\n\nRed leaves at 38.5° from the dashed line.\n\nViolet bends more. It leaves at 39.4°.\n\nThe other colors fill the gap. In diamond, the fan is 0.84° wide.\n\nNow moissanite, at the same facet and the same angle inside.\n\nThe fan opens to 2.14°, about 2.5 times as wide as in diamond.\n\nEvery facet the light crosses opens the fan further.\n\nThe Wheel measures fire in 3D. T73: 78 in diamond, 97 in moissanite.\n\nAcross the 37 cuts we score, moissanite out-fires diamond in 36.\n\nThe one exception: DG-Elongated Hexagon, 97 in diamond and 93 in moissanite.\n\n## The difference you see first\n\nPut a diamond and a moissanite under the same spotlight and turn them. Long before anyone mentions refractive index or doubled facets, one thing jumps out. The moissanite throws flashes of red, orange, green and blue that are bigger, brighter and more frequent.\n\nThat's **fire**. Of all the optical differences between these two stones, it's the one you'll see first and see most. This page shows where fire comes from, how big the gap is, and when fire vanishes.\n\n## Every color bends differently\n\n[Refractive index](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-refractive-index-and-cut) decides how much a stone bends light. Here's the twist: the index isn't one number. It's slightly higher for violet light than for red. White light is a mix of every color. When it crosses a facet at an angle, the violet part bends a little more than the red part, and the colors fan apart.\n\nThat fan of colors is **dispersion**. It's measured as the difference between the stone's index for a red line and for a violet line of the spectrum (686.7 and 430.8 nm):\n\n- **Diamond:** 0.044\n- **Moissanite:** 0.104, about 2.4 times as much.\n\nEvery time light passes through a facet, the fan opens a little further. In moissanite it opens about 2.4 times as wide. So when the light reaches your eye, the colors are far enough apart to see as separate flashes. Moissanite's index, critical angle and weight differ from diamond's by around a tenth. Its dispersion is more than double.\n\n## A prism you can play with\n\nA prism is dispersion you can watch. Our Spectroscope has one: a 60° prism of dense flint glass that spreads lamp light into a rainbow. It bends violet (400 nm) by about 75.5° and red (700 nm) by about 64.7°. So the colors land about 11° apart. A faceted gem does the same thing at every facet, many times over, in every direction.\n\n![Diamond through the Spectroscope's prism: the full rainbow, no lines.](https://digitalgemology.com/img/learn/dm-l4-diamond-prism-spectrum.webp?v=852d3d20)\n\nDiamond through the Spectroscope's prism: the full rainbow, no lines.\n\nVideo: [The T73 in diamond and in moissanite under red carpet flashes](https://www.youtube.com/watch?v=nJ-fw5dl_pk)\n\nThe T73 in diamond and in moissanite turning under the same red carpet flashes. · 10 s · No sound\n\n### Try it yourself\n\n1. **The prism.** Open [Spectroscope](https://digitalgemology.com/tools/spectroscope) and choose diamond (it absorbs nothing, so the spectrum is clean). Set **Spread by** to **Prism**. That rainbow is dispersion.\n2. **The scoreboard.** Open [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel) with the [T73](https://digitalgemology.com/cuts/t73-round-brilliant) in moissanite. (`?cut=t73-round-brilliant&stone=moissanite&vsstone=diamond` compares it with the T73 in diamond.) Read brilliance, fire and scintillation for both.\n3. **The light show.** Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the T73 in moissanite, **Turn** set to Slow. Go through four lightings: **Cloudy day**, **Sunny day**, **Red carpet**, **Club**. Then switch to diamond and repeat.\n4. **The hunt.** Go back to the Wheel. Set the comparison gemstone to diamond and try other cuts. Find: (a) the cut where moissanite gains the most fire over diamond; (b) the one cut where diamond comes out ahead.\n\n## What the tools show\n\n**The scoreboard.** The T73 in moissanite scores 97 for fire against 78 in diamond: 19 points more. Brilliance goes the other way, 86 against 93. Scintillation doesn't move at all (80 and 80): sparkle comes from the pattern of facets, and the cut is the same. Of the three, fire is where the stones differ most. GIA's researchers saw the same in 1997: dispersion well above diamond's, brilliance slightly below.\n\nVideo: [The Cut Performance Wheel, the T73 in diamond giving way to moissanite](https://www.youtube.com/watch?v=qfKQ8hZa5lE)\n\nThe Cut Performance Wheel, the T73 in diamond giving way to the T73 in moissanite, fire growing past it. · 10 s · No sound\n\n**The hunt.** Across the 37 cuts we score, moissanite out-fires diamond in 36. The biggest gain is [DG-M5](https://digitalgemology.com/cuts/dg-m5), a cut drawn for moissanite: fire 67 in diamond, 100 in moissanite. The one exception is DG-Elongated Hexagon: 97 in diamond against 93 in moissanite. It pays for that fire with a brilliance of only 12 in diamond and 20 in moissanite. Diamond's fieriest cuts are fancy shapes that trade brilliance for color: the Oval reaches 92 for fire but only 47 for brilliance. The ten best brilliants in diamond (ranked on our gemstone page) top out at 82 for fire. All ten of the best brilliants in moissanite score 90 or more.\n\n**The light show.** Under a cloudy sky, soft light arrives from everywhere. The colored fans overlap and wash out, and even moissanite looks calm and white. Under direct sun, colored flashes appear. Then come the photographers' flashes on the red carpet and the isolated spots of the club. There the moissanite erupts with color. Under exactly the same light, the diamond flashes less often and in smaller sparks. Fire needs small, bright light sources: the same moissanite can look quiet at the office and like a prism at dinner.\n\n![The same moissanite under a cloudy sky and in direct sun.](https://digitalgemology.com/img/learn/dm-l4-moissanite-cloudy-vs-sunny.webp?v=b57c88e7)\n\nThe same moissanite under a cloudy sky and in direct sun.\n\nVideo: [Diamond and moissanite rocked side by side in sunlight](https://www.youtube.com/watch?v=fZVsk1Zw2ws)\n\nDiamond and moissanite rocked side by side in sunlight, the same pose and light. · 10 s · No sound\n\nIs more fire better? That's taste. Some people love the rainbow; others feel it gives the stone away. For identification, fire is a hint, never a proof. A well-cut diamond under spotlights shows plenty of fire too.\n\n## Key points\n\n- Fire is the flashes of spectral color that a stone throws. It comes from dispersion: the index is higher for violet than for red.\n- Moissanite's dispersion, 0.104, is about 2.4 times diamond's 0.044: the biggest optical gap between the two stones.\n- In the same T73, moissanite gains 19 points of fire and loses 7 of brilliance. Scintillation is unchanged.\n- Moissanite out-fires diamond in 36 of the 37 cuts we score. DG-M5 gains the most (67 to 100).\n- Fire shows under small, bright lights and almost vanishes under soft, even light. It's a clue, not a proof.\n\n**Go further:** the [moissanite gemstone page](https://digitalgemology.com/gemstones/moissanite) ranks the top ten cuts in moissanite. [DG-M5's cut page](https://digitalgemology.com/cuts/dg-m5) has its files.\n\n## Try it free\n\n- [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel): Compare brilliance, fire and scintillation of two cuts, or one cut in two stones.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n- [Spectroscope](https://digitalgemology.com/tools/spectroscope): Read a gemstone's absorption lines through a prism or a grating.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/fire-the-main-optical-difference)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n- [DG-M5 Cut](https://digitalgemology.com/cuts/dg-m5): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: The loupe test: doubled facet edges in moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test)\n- [Try another topic · Historic diamond cuts: the history of the brilliant: Tolkowsky's 1919 ideal cut: the brilliant that was calculated](https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-refractive-index-and-cut) · [Diamond vs moissanite: all lessons](https://digitalgemology.com/learn/diamond-vs-moissanite) · [All topics](https://digitalgemology.com/learn)"},{"id":"DM-L5","course":"Diamond vs moissanite","lesson_number":5,"title":"The loupe test: doubled facet edges in moissanite","url":"https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test","path":"/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test","markdown":"https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test.md","summary":"How to tell moissanite from diamond with a loupe: look through a crown facet for doubled edges, not straight down. Plus needles, polish lines and girdle.","queries":["how to tell moissanite from diamond","moissanite double refraction","moissanite under a loupe"],"quiz":"https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/doubled-facets-the-loupe-test","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Diamond vs moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite) · 4 min read\n\n# The loupe test: doubled facet edges in moissanite\n\nLook for doubled facet edges with a 10× loupe: through a crown facet, moissanite's pavilion edges show twice, because it is doubly refractive (birefringence 0.043), and diamond never doubles. Don't look only straight down through the table: along moissanite's optic axis, nothing doubles.\n\n## The number you can see\n\nOn the [property card](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-properties), moissanite has a line that diamond doesn't: birefringence, 0.043. Moissanite's [higher index](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-refractive-index-and-cut) changes a whole pattern of light. Birefringence does something smaller and more useful: it doubles the edges you see through the stone. It's the most reliable clue you can check with a loupe. GIA's first study of gem moissanite named it as the way to separate the two.\n\n## Why the edges double\n\nMoissanite is doubly refractive. Light that enters it splits into two rays. The two rays travel at slightly different speeds and bend by slightly different amounts. Look through the stone at a facet edge on the far side. You see the edge twice, along two slightly different paths: two thin lines where there should be one.\n\nDiamond is singly refractive. Light stays one ray, and every edge you see through a diamond is single, from any direction.\n\n## The trap: looking straight down\n\nMoissanite has one direction in which light doesn't split: along its **optic axis**. Cutters usually set that axis straight up through the table, square to it. So when you look straight down through the table, you see no doubling, and the stone can pass for diamond. (A stone cut off its axis can show some doubling even face-up.)\n\nYou have to look another way:\n\n- **Through a crown facet**, at an angle: the pavilion facet edges behind it double.\n- **Through the pavilion**, from below: the crown facet edges double.\n- **Straight down, but focused past the culet**: the reflections of the table and crown facets double.\n\nGIA noted that in larger stones, you can sometimes see the doubling without a loupe.\n\n![The T73 in diamond and in moissanite, looked at from 45° under the grading lamp, traced at the finest quality; enlarge a crown facet of each to see single pavilion edges in diamond and doubled ones in moissanite.](https://digitalgemology.com/img/learn/dm-l5-diamond-vs-moissanite-doubling.webp?v=667b1132)\n\nThe T73 in diamond and in moissanite, looked at from 45° under the grading lamp, traced at the finest quality; enlarge a crown facet of each to see single pavilion edges in diamond and doubled ones in moissanite.\n\n### Try it yourself\n\nUse the biggest window you have. The doubling is a few pixels wide.\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the [T73 Round Brilliant](https://digitalgemology.com/cuts/t73-round-brilliant) in moissanite.\n2. Under **View**, choose **At an angle**. Set **Turn** to Off. Leave **Facet mesh** off: the mesh draws the true edges on top and hides the effect.\n3. Look through a crown facet near you at the pavilion edges behind it. Look for edges that come in pairs, slightly ghosted.\n4. Switch to **Face up**. Look through the table. What happened to the doubling?\n5. Switch the gemstone to diamond and repeat steps 2 to 4.\n\n## What the simulator shows\n\nAt an angle, moissanite's edges seen through the crown come in ghosted pairs. The simulator traces both rays. Its report notes that the effect is strongest through the crown and at an angle. Face-up, through the table, most of the doubling disappears, because you look close to the optic axis. In diamond, every edge stays single at every angle.\n\nDoubling proves that the stone is doubly refractive, so **not diamond**. It doesn't prove moissanite on its own. Other doubly refractive look-alikes, such as synthetic rutile, double too. That's why you collect more clues.\n\n## The other loupe clues\n\nGIA's 1997 study listed what else a loupe or microscope shows in moissanite:\n\n- **Needles**: thin white needles, roughly parallel to each other, that run straight down from the table, along the optic axis. Sometimes fine reflective \"stringers\" in the same direction, and pinpoints.\n- **Rounded facet junctions**, where a diamond's are knife-sharp.\n- **Polish lines that all point the same way, facet after facet.** Diamond is harder in some directions than in others, so the cutter works each of its facets at its own angle. Moissanite has no such grain, so the cutter can work it one way throughout. If the lines on every facet you check run the same way, the stone isn't a diamond. But that still doesn't prove moissanite.\n- **The girdle**: frosted, polished or striated, without the fine hairlike \"bearding\" a diamond girdle can show.\n\nWhat you *don't* find in moissanite is just as telling. None of GIA's samples showed the mineral crystals, feathers, strain or cleavage typical of diamond. A diamond, in turn, can show:\n\n- included crystals;\n- feathers;\n- graining;\n- bearding;\n- a \"natural\" (a bit of the original crystal skin left on the girdle);\n- a waxy to granular girdle surface.\n\nTwo cautions. First, GIA's samples were early material, and polish improved even during the study. So today's moissanite may have sharper edges. The doubling doesn't go away, because it comes from the material itself. Second, GIA's researchers treated what you see under magnification as an indication. In their view, only very experienced eyes can call it diagnostic. Doubling is the strongest of these clues; the others add weight to it.\n\n## Key points\n\n- Moissanite's birefringence doubles the facet edges you see through it. Diamond never doubles.\n- Cutters usually set the optic axis square to the table. So look through a crown facet, through the pavilion, or past the culet, never only straight down.\n- Doubling proves \"not diamond\". Add more clues before you say \"moissanite\".\n- Other loupe clues:\n  - parallel needles that run down from the table;\n  - rounded facet junctions;\n  - polish lines that run one way on every facet;\n  - a frosted, polished or striated girdle.\n- No diamond-type inclusions, strain or cleavage in moissanite.\n\n**Go further:** our [double refraction notes](https://digitalgemology.com/about/how-we-measure/simulator#sim-biref) explain how the simulator traces both rays.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/doubled-facets-the-loupe-test)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Moissanite vs diamond: same size, different carat weight](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-carat-size)\n- [Try another topic · The four Cs of diamonds: How a diamond cut grade is set: proportions, polish and symmetry](https://digitalgemology.com/learn/four-cs/how-diamond-cut-grade-is-determined)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-vs-moissanite/why-moissanite-has-more-fire) · [Diamond vs moissanite: all lessons](https://digitalgemology.com/learn/diamond-vs-moissanite) · [All topics](https://digitalgemology.com/learn)"},{"id":"DM-L6","course":"Diamond vs moissanite","lesson_number":6,"title":"Moissanite vs diamond: same size, different carat weight","url":"https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-carat-size","path":"/learn/diamond-vs-moissanite/moissanite-vs-diamond-carat-size","markdown":"https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-carat-size.md","summary":"Moissanite carat to mm: a 1.00 ct T73 is 6.48 mm in diamond and 6.67 mm in moissanite. At the same size, moissanite weighs about 0.91 times as much.","queries":["moissanite carat to mm","moissanite carat weight vs diamond","diamond equivalent weight"],"quiz":"https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/same-size-different-weight","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Diamond vs moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite) · 3 min read\n\n# Moissanite vs diamond: same size, different carat weight\n\nA 1.00 carat T73 measures 6.48 mm across in diamond and 6.67 mm in moissanite, because moissanite is lighter for its size (specific gravity 3.22 against 3.52). At the same size, moissanite weighs about 0.91 times as much; at the same weight, it is about 3% wider.\n\n## The stone that grew\n\nSwitch a 1.00 carat [T73](https://digitalgemology.com/cuts/t73-round-brilliant) from diamond to moissanite in the simulator, and its measurements grow. You don't touch the weight. The [loupe test](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test) is a test for your eyes. This page gives you a test for a scale and a gauge. It starts from one line of the [property card](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-properties): specific gravity.\n\n## Weight for size\n\nSpecific gravity (SG) compares a stone's weight with the weight of the same volume of water. Diamond is 3.52; moissanite is 3.22.\n\nSo a moissanite is lighter for its size. Two stones of exactly the same shape and size weigh in the ratio 3.22 to 3.52. So the moissanite weighs about **0.91 times** as much as the diamond. GIA's 1997 study gave the same example. A 6.50 mm round diamond weighs about 1.00 carat. A moissanite of the same diameter and cut weighs about 0.91 carat.\n\nTurn it around and the same thing happens in reverse: at the same carat weight, the moissanite is the bigger stone. Not by much. Weight goes with volume, so the width changes with the cube root of the ratio. A moissanite of the same weight is only about 3% wider.\n\nA carat is a unit of weight, 0.2 g, not a unit of size. That's why the same \"1 carat\" can be two different sizes.\n\n![1.00 ct T73s in diamond, moissanite and cubic zirconia at true size, each labeled with its width.](https://digitalgemology.com/img/learn/dm-l6-t73-1ct-diamond-moissanite-cz.webp?v=5dbb3cd3)\n\n1.00 ct T73s in diamond, moissanite and cubic zirconia at true size, each labeled with its width.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the T73 Round Brilliant in diamond at **1** carat. Read the **Measurements** line.\n2. Switch the gemstone to moissanite. Read the measurements again.\n3. Set **2** carats and repeat for both stones.\n4. Work it out. What would a moissanite exactly the size of the 1.00 carat diamond weigh? (Multiply by 3.22 ÷ 3.52.)\n5. Bonus: switch to cubic zirconia at 1 carat.\n\n## What the simulator shows\n\nAt 1.00 carat the T73 measures 6.48 mm across in diamond and 6.67 mm in moissanite. At 2.00 carats, 8.16 mm against 8.41 mm. Both times the moissanite is about 3% wider. A moissanite exactly 6.48 mm across would weigh about 0.91 carat.\n\nThe bonus shows why moissanite is harder to catch than cubic zirconia. CZ is far heavier, SG about 5.8, so 1.00 carat of it is only 5.48 mm across. A CZ sold by weight as a diamond looks small for its carat. A moissanite looks only slightly large. GIA described moissanite as much closer to diamond in \"heft\" than any earlier imitation.\n\n## Using it on a loose stone\n\nFor a loose round stone, measure the diameter with a gauge and weigh the stone on a carat scale. Is the weight low for the size, by roughly a tenth for a well-proportioned round? Then look harder.\n\nIt's a clue, not a verdict: proportions change weight too. A deep stone weighs more for its width than a shallow one, and a thick girdle adds hidden weight. So compare like with like: same shape, similar proportions. The check works much better on a stone with a report. There you can compare the stone with the measurements and weight on paper (see [moissanite certificates vs diamond reports](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-certificate-vs-diamond-report)).\n\nLabs and dealers that sort mixed parcels use a heavy liquid instead. In methylene iodide, SG 3.32, a moissanite floats and a diamond sinks. GIA called specific gravity diagnostic. The liquid is toxic, so this is a lab method, not a kitchen-table one.\n\n## Key points\n\n- Moissanite's specific gravity is 3.22 against diamond's 3.52.\n- At the same size, a moissanite weighs about 0.91 times as much as a diamond.\n- At the same carat weight, a moissanite is about 3% wider: 6.67 mm against 6.48 mm for a 1.00 carat T73.\n- Weight for size is a useful check on a loose stone. It works best when you compare it with a report or with stones of similar proportions.\n- In a heavy liquid of SG 3.32, moissanite floats and diamond sinks.\n\n**Go further:** the [moissanite gemstone page](https://digitalgemology.com/gemstones/moissanite) answers \"How much does moissanite weigh compared with diamond?\" in one line.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/same-size-different-weight)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Moissanite color and fluorescence compared with diamond](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-color-and-fluorescence)\n- [Try another topic · Historic diamond cuts: the history of the brilliant: Old European cut diamonds: when the outline went round](https://digitalgemology.com/learn/historic-cuts/old-european-cut-diamond)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test) · [Diamond vs moissanite: all lessons](https://digitalgemology.com/learn/diamond-vs-moissanite) · [All topics](https://digitalgemology.com/learn)"},{"id":"DM-L7","course":"Diamond vs moissanite","lesson_number":7,"title":"Moissanite color and fluorescence compared with diamond","url":"https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-color-and-fluorescence","path":"/learn/diamond-vs-moissanite/moissanite-color-and-fluorescence","markdown":"https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-color-and-fluorescence.md","summary":"Moissanite color grades: D to F since 2015, from the producer or IGI, not GIA. Early moissanite tints, and what a UV lamp shows in each stone.","queries":["moissanite color grades","does moissanite turn yellow","moissanite fluorescence"],"quiz":"https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/color-and-fluorescence","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Diamond vs moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite) · 3 min read\n\n# Moissanite color and fluorescence compared with diamond\n\nColorless moissanite has been sold in D, E and F grades since 2015, but those letters come from the producer or IGI, not from GIA's diamond scale. Early moissanite had gray, green or yellow tints, so GIA's 1997 research grades, from about I to U–V, were only approximate.\n\n## Colorless isn't one color\n\nPut a diamond and a moissanite side by side on a white tray, table down, as graders do when they look at color. Two \"colorless\" stones rarely match exactly. A faint tint shows, and the kind of tint matters.\n\n## How diamond color is graded\n\nOn a GIA report, the color of a near-colorless diamond is a single letter on the **D-to-Z scale**. The scale measures how little color there is. D shows none, and each letter further down the alphabet shows a little more yellow or brown. Graders judge the letter by setting the stone beside reference diamonds of known grade. If the lab found a color treatment, the letter carries an asterisk. Diamonds with more color than Z, or with other colors, are graded as **fancy colors**.\n\nThe scale is built for the tints diamonds actually have: yellow and brown.\n\n## Moissanite's tint\n\nWhen GIA studied the first gem moissanite in 1997, its stones ranged from near-colorless to light yellow, green and gray. Graders tried to give them diamond-equivalent grades, for research only, because GIA doesn't grade simulants. The best came out around I; others went down to U–V. Face-up, the better ones, around I to K, passed for colorless. Tint became visible from roughly L to N. The real problem was the **kind** of tint. Gray and green hues fall outside a scale built on yellow and brown, so the grades could only be approximate.\n\nProduction has moved on. In 2015, the original producer of moissanite launched its first colorless line. Since then, moissanite has been sold in D, E and F grades. Those letters come from the producer or from IGI (see [moissanite certificates](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-certificate-vs-diamond-report)), not from GIA's diamond scale. Moissanite also comes in colors. GIA has examined blue-green, brown-yellow and deep green moissanites offered as colored diamonds.\n\n## Fluorescence\n\nSome stones glow under ultraviolet light. A GIA diamond report has a line for it, **Fluorescence**. It describes how strong the glow is and what color it is, under long-wave UV. A report that says \"None\" can still hide a glow too faint to grade. Fluorescence doesn't change the color or clarity grade; it describes the stone.\n\nMany near-colorless diamonds fluoresce, mostly **blue**. Many don't. In GIA's 1997 study, 19 of 23 moissanites were **inert** under long-wave UV. The other four glowed **weak to moderate orange**. Only one reacted to short-wave UV.\n\nSo a blue glow points to diamond. A dark, inert stone proves nothing, because many diamonds are inert too.\n\n![Under the UV lamp, a diamond with strong blue fluorescence beside a moissanite staying dark.](https://digitalgemology.com/img/learn/dm-l7-diamond-vs-moissanite-uv.webp?v=f257a359)\n\nUnder the UV lamp, a diamond with strong blue fluorescence beside a moissanite staying dark.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the [T73](https://digitalgemology.com/cuts/t73-round-brilliant) in diamond. Under **Color grade**, choose the **K–M** range and **K**.\n2. Switch the gemstone to moissanite and keep K. Compare the tint face-up, then face-down.\n3. Go back to diamond. Set **Fluorescence** to **Strong**, and choose the **UV lamp** lighting.\n4. Set Fluorescence back to **None**. Then switch to moissanite under the same lamp.\n\n## What the simulator shows\n\nAt the same letter, the two tints aren't quite the same. The simulator gives moissanite its own body color, a little greener than diamond's yellow. On a real tray, this difference in hue, not just in depth, made early moissanite hard to grade.\n\n![Color K in diamond and in moissanite under the grading lamp.](https://digitalgemology.com/img/learn/dm-l7-t73-k-diamond-vs-moissanite.webp?v=7a8017d1)\n\nColor K in diamond and in moissanite under the grading lamp.\n\nUnder the UV lamp, the diamond with strong fluorescence glows blue. Set to None, it stays dark. The moissanite has no fluorescence setting at all, because in the simulator only diamond is graded for it. It stays dark, like an inert diamond. That's the point: a stone that stays dark under UV can be either one.\n\nThere's one more UV difference, and it shows up in instruments. Moissanite absorbs near-ultraviolet light that diamond lets through. An early moissanite tester used exactly that. After a thermal tester said \"diamond\", it checked whether near-UV passed through the stone. Our page on [diamond testers and moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite) picks that up.\n\n## Key points\n\n- Diamond color is graded D to Z for the absence of yellow or brown, against master stones. Stronger colors are fancy colors.\n- Early moissanite had gray, green or yellow tints that didn't fit a scale built on yellow and brown. Colorless D–F moissanite has been sold since 2015.\n- Moissanite color letters come from producers or IGI, not from GIA's diamond grading.\n- Many diamonds fluoresce blue under long-wave UV. Most moissanite is inert; a few glow weak orange.\n- A blue glow points to diamond. No glow proves nothing.\n\n**Go further:** the [simulator's notes on color, clarity and fluorescence](https://digitalgemology.com/about/how-we-measure/simulator) explain how the tints and the UV glow are drawn.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/color-and-fluorescence)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Diamond testers and moissanite: what the instruments say](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite)\n- [Try another topic · Diamond anatomy and proportions: The parts of a diamond: crown, girdle and pavilion](https://digitalgemology.com/learn/diamond-anatomy/parts-of-a-diamond)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-carat-size) · [Diamond vs moissanite: all lessons](https://digitalgemology.com/learn/diamond-vs-moissanite) · [All topics](https://digitalgemology.com/learn)"},{"id":"DM-L8","course":"Diamond vs moissanite","lesson_number":8,"title":"Diamond testers and moissanite: what the instruments say","url":"https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite","path":"/learn/diamond-vs-moissanite/diamond-tester-and-moissanite","markdown":"https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite.md","summary":"Does moissanite pass a diamond tester? A thermal tester says \"diamond\" for both. What electrical testers, screeners and the polariscope show.","queries":["does moissanite pass a diamond tester","moissanite tester","polariscope moissanite"],"quiz":"https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/what-the-instruments-and-testers-say","tools":["https://digitalgemology.com/tools/polariscope","https://digitalgemology.com/tools/refractometer","https://digitalgemology.com/tools/spectroscope","https://digitalgemology.com/tools/dichroscope"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Diamond vs moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite) · 4 min read\n\n# Diamond testers and moissanite: what the instruments say\n\nYes, a thermal tester: moissanite conducts heat almost as well as diamond, and in GIA's study every moissanite read \"diamond\". An electrical tester flags many moissanites (13 of 23), but some gray and blue diamonds conduct too; a polariscope, used away from the optic axis, separates the two.\n\nVideo: [Diamond with strain in the polariscope (illustrative)](https://www.youtube.com/watch?v=hPiyusVqrrY)\n\nDiamond with strain (illustrative): patchy light that never goes dark all at once. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nDiamond with strain (illustrative): patchy light that never goes dark all at once.\n\n## Not every test is a test\n\nSome differences you can't see. Moissanite absorbs near-ultraviolet light that diamond lets through (see [color and fluorescence](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-color-and-fluorescence)). Gem labs and jewelers use instruments to turn differences like that into a reading. But an instrument only helps if the two stones read differently on it. For diamond and moissanite, several classic instruments give the same answer for both. A few give an answer that looks like proof and isn't.\n\n## The four gem instruments\n\n**Refractometer.** It reads refractive index, up to the limit of its contact liquid, 1.81. Diamond (2.417) and moissanite (2.648 to 2.691) are both far above it. So both read **over the limit (OTL)**: no number, no edges, and moissanite's double refraction stays hidden. Cubic zirconia reads the same way. Result: no separation.\n\n**Dichroscope.** It shows whether a stone sends out different colors in different directions. Both stones are colorless, so the two windows match for both. Moissanite does split light into two rays, but it absorbs neither ray, so they leave with the same color. Result: no separation. Also a reminder: \"no difference\" doesn't prove that a stone is singly refractive.\n\n![Moissanite through the dichroscope: the two windows alike.](https://digitalgemology.com/img/learn/dm-l8-moissanite-dichroscope.webp?v=7f3550ce)\n\nMoissanite through the dichroscope: the two windows alike.\n\n**Spectroscope.** It shows dark lines where a stone absorbs light. Our model treats both stones as perfectly colorless and shows an unbroken spectrum for both. Real stones can differ at the violet end. Many near-colorless diamonds show a fine line at 415 nm. Moissanite absorbs everything below about 425 nm. GIA noted that both are easy to misread with a hand spectroscope. Result: a hint for experienced eyes, not a test.\n\n![Moissanite's modeled spectrum: unbroken.](https://digitalgemology.com/img/learn/dm-l8-moissanite-spectrum.webp?v=7e909f25)\n\nMoissanite's modeled spectrum: unbroken.\n\n**Polariscope.** Two crossed polarizing filters, with the stone between them. A singly refractive stone stays dark as it turns. A doubly refractive stone blinks: light and dark four times a turn. This instrument **does** separate diamond and moissanite, if you use it right.\n\nVideo: [Moissanite down its optic axis in the polariscope](https://www.youtube.com/watch?v=i5UwXOB0XA4)\n\nMoissanite looked at down its optic axis, staying dark as it turns. · 10 s · No sound\n\nVideo: [Moissanite across the axis in the polariscope](https://www.youtube.com/watch?v=ymkD8929yek)\n\nAcross the axis, four light and four dark positions a turn. · 10 s · No sound\n\n![The conoscope's uniaxial figure with the red plate in.](https://digitalgemology.com/img/learn/dm-l8-moissanite-conoscope-red-plate.webp?v=c8d7cda1)\n\nThe conoscope's uniaxial figure with the red plate in.\n\n### Try it yourself\n\n1. Open [Refractometer](https://digitalgemology.com/tools/refractometer) and choose diamond, then moissanite. Read the eyepiece both times.\n2. Open [Polariscope](https://digitalgemology.com/tools/polariscope). Choose **Moissanite** and the **[T73 Round Brilliant](https://digitalgemology.com/cuts/t73-round-brilliant)** shape. Drag the **Tilt** slider to **0°**. Now you look straight down the optic axis, as you would through the table. Turn the stone.\n3. Drag the tilt to **90°**, across the axis. Turn the stone again.\n4. Turn on the **Conoscope** and set the tilt back to 0°. Then add the **Red plate**.\n5. Choose **Diamond** and turn on **Strain**. Turn the stone.\n\n## What the Refractometer and Polariscope show\n\nThe refractometer gave the same non-reading twice: over the limit.\n\nThe polariscope sprang the trap from the [loupe test](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test). Straight down the optic axis, moissanite **stayed dark** as it turned, exactly like a singly refractive stone. Our tool says so: dark is not always singly refractive. GIA described this trap in 1997. Face-down, all its moissanites passed for singly refractive. They showed their double refraction only from other sides, the girdle above all. Tilted away from the axis (the tool's 90° looks straight across it), the moissanite **blinked**. The conoscope showed a uniaxial interference figure. The red plate turned it blue in the northeast quadrant: **optically positive**.\n\nDiamond stays dark at every turn and tilt. With strain on, it shows patchy gray light that never goes dark all at once. Many diamonds carry internal strain, which makes them weakly doubly refractive in patches. A truly doubly refractive stone goes dark everywhere at once, four times a turn. Between these two stones, strain points to diamond: GIA saw no strain in moissanite.\n\n## The testers\n\n**Thermal testers** measure how fast the stone draws heat from a hot tip. Diamond conducts heat extremely well, and so does moissanite. In GIA's study, every moissanite read \"diamond\" on every thermal tester tried. A thermal \"diamond\" means diamond **or moissanite**.\n\n**Electrical testers** check whether the stone conducts electricity. Many moissanites do (13 of the 23 GIA tested), and most near-colorless diamonds don't. But some gray and blue diamonds conduct as well. A blue diamond that conducts is type IIb, colored by boron, and labs grow boron-blue diamonds too. GIA's study called conductivity an indication, never a diagnosis. So a \"moissanite\" reading on a blue or gray stone needs a lab. Combined testers use a thermal reading and a second reading together. The first one, in 1997, checked near-UV transparency after the thermal test.\n\n**Screening devices**, such as GIA's DiamondCheck and iD100, separate natural diamonds from laboratory-grown diamonds and simulants. Most answer **Pass** (natural) or **Refer**. A referred stone may still be natural, and it goes to a lab. One warning matters here. Depending on how it tests, a screener may fail to refer a simulant and pass it as natural. So know what your device covers before you trust a Pass on a moissanite.\n\n**The lab** settles it with spectra. Moissanite's Raman spectrum lacks diamond's peak at 1332 cm⁻¹. Its infrared spectrum looks nothing like diamond's. And X-ray fluorescence finds silicon, which an untreated diamond doesn't contain. That's how GIA identifies moissanites submitted as diamonds today.\n\n## Key points\n\n- Refractometer, dichroscope and (in practice) spectroscope don't separate colorless diamond and moissanite.\n- The polariscope does. Diamond stays dark (strain shows as patchy light). Moissanite blinks when you look at it away from its optic axis, for example through the girdle, not straight down through the table.\n- A thermal tester reads both as \"diamond\".\n- An electrical tester flags most moissanite, but some blue or gray diamonds conduct too.\n- Screeners answer Pass or Refer. A lab confirms with Raman and infrared spectra.\n\n**Go further:** the [Polariscope's How we measure page](https://digitalgemology.com/about/how-we-measure/polariscope) explains blinking, strain and the red plate.\n\n## Try it free\n\n- [Polariscope](https://digitalgemology.com/tools/polariscope): Turn a gemstone between crossed polarizers and read its optic figure.\n- [Refractometer](https://digitalgemology.com/tools/refractometer): Read the shadow edges of seven gemstones on a gem refractometer.\n- [Spectroscope](https://digitalgemology.com/tools/spectroscope): Read a gemstone's absorption lines through a prism or a grating.\n- [Dichroscope](https://digitalgemology.com/tools/dichroscope): See the two colors of a gemstone side by side in a dichroscope.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/what-the-instruments-and-testers-say)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Moissanite certificates vs diamond grading reports](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-certificate-vs-diamond-report)\n- [Try another topic · The four Cs of diamonds: Carat weight vs size: why a 2 ct diamond isn't twice as big](https://digitalgemology.com/learn/four-cs/carat-weight-vs-size)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-color-and-fluorescence) · [Diamond vs moissanite: all lessons](https://digitalgemology.com/learn/diamond-vs-moissanite) · [All topics](https://digitalgemology.com/learn)"},{"id":"DM-L9","course":"Diamond vs moissanite","lesson_number":9,"title":"Moissanite certificates vs diamond grading reports","url":"https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-certificate-vs-diamond-report","path":"/learn/diamond-vs-moissanite/moissanite-certificate-vs-diamond-report","markdown":"https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-certificate-vs-diamond-report.md","summary":"Moissanite certificate vs diamond grading report: GIA identifies moissanite but doesn't grade it, IGI grades one producer's stones. How to check a report.","queries":["moissanite certificate","does moissanite come with a certificate","gra moissanite certificate"],"quiz":"https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/reports-and-paperwork","tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Diamond vs moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite) · 4 min read\n\n# Moissanite certificates vs diamond grading reports\n\nA moissanite certificate is not a diamond grading report. GIA issues only an Identification Report for moissanite; IGI has graded one producer's moissanite since May 2024, and other moissanite gets an identification report, a certificate of authenticity or only a seller's card.\n\n## From the lab bench to the paper\n\nIn the end, a lab settles what a stone is, with spectra (see [diamond testers and moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite)). A lab writes its findings down, and that document travels with the stone. The type of document is itself a clue: diamond and moissanite don't get the same paper.\n\n## What a diamond gets\n\nGIA tests every stone it receives. The tests confirm whether the stone is diamond, and whether it is natural or laboratory-grown.\n\n- A **natural diamond** gets a grading report. The report gives its four Cs (carat, color, clarity, cut), measurements, proportions, finish, fluorescence, any inscription and comments. The report number can be laser-inscribed on the girdle.\n- A **laboratory-grown diamond** gets a document that you can't mistake for a natural diamond's report. Since 1 October 2025, GIA rates a colorless to near-colorless lab-grown diamond Premium or Standard, with no D-to-Z color or clarity grade. Before that, GIA's digital Laboratory-Grown Diamond Report graded it on the same principles as a natural diamond. Its girdle carries the number plus the word LABORATORY-GROWN.\n\n## What a moissanite gets\n\nSend GIA a moissanite, and GIA examines it just as thoroughly. But the moissanite comes back with a different document, an **Identification Report**, because GIA doesn't grade simulants. Expect no D-to-Z letter and no clarity grade. For comparison, GIA's identification reports for colored stones list:\n\n- the item's details (weight, measurements, shape, color, cutting style);\n- the result (what the material is, with laboratory-grown material labeled as such);\n- comments.\n\nWe haven't seen a moissanite one, so we can't quote its exact wording.\n\nSince May 2024, **IGI** has issued grading reports for one producer's moissanite:\n\n- cut and clarity on IGI's usual standards;\n- color graded individually only for D and E, with F written as \"colorless\" and G–H as \"near colorless\";\n- every stone laser-inscribed by IGI.\n\nMoissanite from other producers gets an IGI identification report or a certificate of authenticity.\n\nMany moissanites come only with a card from the seller or the brand. That card can be useful, for example as a warranty, but it isn't an independent lab report. Ask who issued it, and whether you can look its number up.\n\n## When the paper lies\n\nIn Lab Notes published in 2020 and 2022, GIA described moissanites that carried a **fake GIA inscription**. In one case, a 1.02 carat round came in for a diamond grading report. It carried the number of a real report, for an E-color natural diamond of the same weight, graded the year before. The weight matched. The **measurements didn't**, and the lettering of the inscription wasn't GIA's.\n\n[Same size, different weight](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-carat-size) explains why the weight can match but the size can't: at the same carat weight, a moissanite is about 3% wider.\n\n![The same 1.00 ct in diamond and in moissanite at true size: 6.5 against 6.7 mm.](https://digitalgemology.com/img/learn/dm-l6-t73-1ct-diamond-moissanite-cz.webp?v=5dbb3cd3)\n\nThe same 1.00 ct in diamond and in moissanite at true size: 6.5 against 6.7 mm.\n\n![The report header for a 1.00 ct T73 in diamond and in moissanite, with the measurements circled.](https://digitalgemology.com/img/learn/dm-l9-report-header-measurements.webp?v=d600c282)\n\nThe report header for a 1.00 ct T73 in diamond and in moissanite, with the measurements circled.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the [T73 Round Brilliant](https://digitalgemology.com/cuts/t73-round-brilliant) in diamond at **1** carat. Treat its report as \"the paper\". Write down the carat weight and the measurements.\n2. Now play the stone that arrives with that paper. Switch the gemstone to moissanite, keep 1 carat, and read the measurements.\n3. Compare the two lines. Which field on a report would give the swap away?\n4. Scroll through the moissanite's report. Find two rows that a diamond grading report wouldn't have. Then find the line at the bottom that says what this document is.\n\n## What the simulator report shows\n\n\"The paper\" says 1.00 carat, 6.48 – 6.48 × 4.00 mm. The moissanite weighs exactly the same and measures 6.67 – 6.67 × 4.12 mm. The weight checks out. The measurements are off by about 0.2 mm, and a gauge or a lab spots that immediately. So to check a report, check the stone against it. Look the number up on GIA's Report Check. Then compare **weight and measurements**, not just the number on the girdle.\n\nThe moissanite's report shows a **Birefringence** of 0.043 and an **Origin** locked to Laboratory-grown. It also lets you set color and clarity grades, so you can learn the scales. A GIA document wouldn't grade a moissanite at all. The last line says it plainly: a simulation, not a grading report.\n\n## Key points\n\n- GIA tests every stone. A natural diamond gets a grading report. A lab-grown diamond gets its own document: since 1 October 2025, a Premium or Standard assessment.\n- GIA issues no grading report for simulants. A moissanite gets an Identification Report, with no color or clarity grade.\n- IGI has graded one producer's moissanite since 2024. Other moissanite gets an identification report or a certificate of authenticity.\n- A seller's or brand's card isn't an independent lab report.\n- Check the stone against its report. Look up the number, then compare weight and measurements. A moissanite with a diamond's weight is about 3% wider.\n\n**Go further:** our pages on [how to read a diamond grading report](https://digitalgemology.com/learn/grading-reports) walk through every field of a diamond report.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/reports-and-paperwork)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Moissanite vs diamond: wear, care and cleaning](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-durability-and-care)\n- [Try another topic · The bow-tie effect: Fixing a bow-tie: the steep belly of DG-Bowtie](https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite) · [Diamond vs moissanite: all lessons](https://digitalgemology.com/learn/diamond-vs-moissanite) · [All topics](https://digitalgemology.com/learn)"},{"id":"DM-L10","course":"Diamond vs moissanite","lesson_number":10,"title":"Moissanite vs diamond: wear, care and cleaning","url":"https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-durability-and-care","path":"/learn/diamond-vs-moissanite/moissanite-vs-diamond-durability-and-care","markdown":"https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-durability-and-care.md","summary":"Moissanite durability vs diamond: hardness, cleavage, heat and cleaning. Then a step-by-step routine that ends in diamond, not diamond, or a lab.","queries":["moissanite durability","how to clean moissanite","does moissanite scratch"],"quiz":"https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/wear-care-and-your-bench-routine","tools":["https://digitalgemology.com/tools/polariscope","https://digitalgemology.com/tools/3d_gemstone_simulator","https://digitalgemology.com/tools/refractometer"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Diamond vs moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite) · 4 min read\n\n# Moissanite vs diamond: wear, care and cleaning\n\nMoissanite (Mohs 9.25) is harder than sapphire, showed no cleavage, and is reportedly stable in air to 1700 °C. Diamond (Mohs 10) resists scratches better but can cleave; neither stone is unbreakable, and moissanite's girdle can chip under hard wear.\n\n## Living with each stone\n\nThis page is about the stone on a hand. Then it puts in order every check from our pages on [diamond vs moissanite](https://digitalgemology.com/learn/diamond-vs-moissanite).\n\n**Scratches.** Diamond is the hardest gem: Mohs 10. Moissanite, at 9.25, is harder than sapphire (9). The real gap up to diamond is larger than those numbers suggest (see [the property card](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-properties)).\n\n**Knocks.** Hardness doesn't stop chipping; toughness does. Diamond's toughness is good along its cleavage directions and exceptional in others. So a hard knock in the wrong direction can split or chip it. GIA found no cleavage in moissanite. It breaks with curved, shell-like fractures, and its girdle could chip under hard wear. Neither stone is unbreakable.\n\n**Heat.** Moissanite is reportedly stable in air to 1700 °C. GIA's researchers saw moissanites cast in place in a gold ring without apparent damage. They expected no problem with prong repairs while the stone stays in place.\n\n**Cleaning.** For diamond, GIA's cleaning chart adds a caution to ultrasonic and steam cleaning for stones with feathers, many inclusions or a fracture filling. For moissanite, GIA did no durability testing of its own. The producer reported no problems with ordinary setting, repair and cleaning.\n\n## The bench routine\n\nHere are the checks in order, from free to lab, with what each result **proves**. The most important rule comes from GIA's first study. Many tests prove that a stone is **not diamond**. No single test proves that it is **moissanite**.\n\n| Step | Check | Points to moissanite | What it proves |\n| --- | --- | --- | --- |\n| 1 | Look under spotlights ([fire](https://digitalgemology.com/learn/diamond-vs-moissanite/why-moissanite-has-more-fire)) | Strong, broad colored flashes | Nothing; a hint |\n| 2 | Loupe through a crown facet ([loupe test](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test)) | Doubled pavilion edges | Not diamond |\n| 3 | Loupe: inclusions, edges, polish, girdle ([loupe test](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test)) | Parallel needles running down from the table; rounded edges; polish lines that run one way on every facet; frosted, polished or striated girdle | Hints; one-way polish lines on every facet rule out diamond |\n| 4 | Weight against size, loose stone ([carat and size](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-carat-size)) | About a tenth light for its size | A strong hint |\n| 5 | UV lamp ([fluorescence](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-color-and-fluorescence)) | Inert or orange | Blue points to diamond; dark proves nothing |\n| 6 | Thermal tester ([testers](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite)) | \"Diamond\" | Diamond or moissanite |\n| 7 | Electrical or combined tester ([testers](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite)) | \"Moissanite\" | Strong hint; refer blue or gray stones |\n| 8 | Polariscope, in two directions ([instruments](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite)) | Blinks when viewed away from the optic axis | Not diamond |\n| 9 | Paperwork ([certificates and reports](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-certificate-vs-diamond-report)) | Identification report, seller card, or a report whose measurements don't match | Depends on the document; check the stone against it |\n| 10 | Lab: Raman, infrared ([the lab](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite)) | No 1332 cm⁻¹ peak, silicon present | Identification |\n\nTwo more rules of thumb. First, write each result down as you go, including the results that prove nothing. Second, this routine separates moissanite from diamond. It can't tell a natural diamond from a laboratory-grown one. That needs a screening device or a lab.\n\n![The routine as a two-column checklist, diamond and moissanite, with pictures from these pages beside the steps that have one.](https://digitalgemology.com/img/learn/dm-l10-bench-routine-checklist.webp?v=d9b1de36)\n\nThe routine as a two-column checklist, diamond and moissanite, with pictures from these pages beside the steps that have one.\n\n### Try it yourself\n\nRun the routine on screen, one column per stone. Use the same cut in both.\n\n1. **Look:** open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the [T73](https://digitalgemology.com/cuts/t73-round-brilliant), **Club** lighting and a slow turn. Note the fire.\n2. **Loupe:** set **At an angle** and turn the facet mesh off. Doubled edges, yes or no?\n3. **Weight for size:** set 1 carat. Note the measurements.\n4. **UV:** choose the **UV lamp** lighting. For diamond, try Fluorescence None and Strong.\n5. **Refractometer and Polariscope:** open [Refractometer](https://digitalgemology.com/tools/refractometer), then [Polariscope](https://digitalgemology.com/tools/polariscope) at 0° and 90° tilt.\n6. **Paper:** read the simulator's report rows for Origin and Birefringence.\n\n## What the routine shows\n\nOn the stone itself, the two columns split in three places, and nowhere else for certain:\n\n- at the loupe (step 2);\n- at the measurements (step 3);\n- at the polariscope, tilted across the axis (step 5).\n\nThe paper split too (step 6): a birefringence of 0.043 against none, and an origin locked to laboratory-grown. On a real stone, the paper is only as good as the document behind it (see [moissanite certificates vs diamond reports](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-certificate-vs-diamond-report)). Fire leaned toward moissanite but proved nothing. The UV lamp only spoke when the diamond glowed. The refractometer gave the same answer twice.\n\nThat's what a good routine looks like: several independent checks that agree, each one cheap, and a clear point where you stop and send the stone to a lab.\n\n## Key points\n\n- Diamond (Mohs 10) resists scratches best but can cleave. Moissanite (9.25) showed no cleavage but can chip at the girdle.\n- Moissanite is reportedly stable at high heat, and GIA saw stones cast in place without apparent damage.\n- For diamond, take care with ultrasonic and steam if it has feathers, many inclusions or a fracture filling.\n- Many tests prove \"not diamond\". No single test proves \"moissanite\". Combine independent checks.\n- The routine separates moissanite from diamond, not natural from laboratory-grown diamond.\n\n**Go further:** take the [diamond vs moissanite quiz](https://digitalgemology.com/skool/quiz/diamond-vs-moissanite). Then read our pages on [how to read a diamond grading report](https://digitalgemology.com/learn/grading-reports) for every field of a diamond report.\n\n## Try it free\n\n- [Polariscope](https://digitalgemology.com/tools/polariscope): Turn a gemstone between crossed polarizers and read its optic figure.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n- [Refractometer](https://digitalgemology.com/tools/refractometer): Read the shadow edges of seven gemstones on a gem refractometer.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/diamond-vs-moissanite/wear-care-and-your-bench-routine)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Try another topic · Diamond anatomy and proportions: Crown angle and crown height in a round diamond](https://digitalgemology.com/learn/diamond-anatomy/diamond-crown-angle)\n\n[Previous lesson](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-certificate-vs-diamond-report) · [Diamond vs moissanite: all lessons](https://digitalgemology.com/learn/diamond-vs-moissanite) · [All topics](https://digitalgemology.com/learn)"},{"id":"HB-L1","course":"The history of the brilliant","lesson_number":1,"title":"The old single cut: eight facets and a lot of fire","url":"https://digitalgemology.com/learn/historic-cuts/old-single-cut-diamond","path":"/learn/historic-cuts/old-single-cut-diamond","markdown":"https://digitalgemology.com/learn/historic-cuts/old-single-cut-diamond.md","summary":"The single cut diamond of the 1400s: 8 facets above the girdle, 18 in all. Why it throws more fire than a modern round but barely sparkles.","queries":["single cut diamond","old single cut","eight cut diamond"],"quiz":"https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/the-old-single-eight-facets-and-a-lot-of-fire","tools":["https://digitalgemology.com/tools/cut-performance-wheel","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/old-single","https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Historic diamond cuts: the history of the brilliant](https://digitalgemology.com/learn/historic-cuts) · 4 min read\n\n# The old single cut: eight facets and a lot of fire\n\nThe single cut, or eight cut, flattens the top of a diamond octahedron into a table and bevels the corners to an octagon: 8 facets above the girdle, 18 in all. On our Wheel it beats the modern T73 on fire (84 vs 78) but scores only 44 for scintillation.\n\nVideo: [The old single beside the T73 in direct sun](https://www.youtube.com/watch?v=MqbJ1CR_buQ)\n\nThe old single beside the T73 in direct sun, at true size: big, separate flashes against many small ones. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nThe old single beside the T73 in direct sun, at true size: big, separate flashes against many small ones.\n\n## A crystal that was already a gem\n\nFor most of history, a diamond in jewelry was a crystal as it came out of the ground. That crystal is an octahedron: two four-sided pyramids joined at their bases. People prized it for its hardness and its mirror-like luster, not for colored flashes. In paintings of the period, table-cut diamonds look almost black.\n\nOur [history of the brilliant](https://digitalgemology.com/learn/historic-cuts) follows that crystal for six hundred years, one cut at a time. For each cut we ask two questions: what technology made it possible, and what did it change in the light?\n\n## The technology: a wheel and diamond dust\n\nOnly diamond scratches diamond. So the only way to shape one was to grind it with its own powder. The first firm record is a guild of diamond polishers in Nuremberg in 1375, with an apprenticeship of five to six years. Around 1476, Lodewyk van Berquem, a polisher in Bruges, became famous for something new: facets laid out with strict symmetry. His family later claimed he invented polishing with diamond powder. Tolkowsky, writing in 1919, points out that polishing was a century older. What Van Berquem may have added is a better iron wheel, one that held the powder well.\n\nDemand pushed the craft forward. From about 1450, it became fashionable at the French court for women to wear diamonds as jewels. The fashion spread across Europe. More orders meant more cutters, and more ideas.\n\nStill, every cut of this era was a compromise with the crystal. The French traveler Tavernier described Indian cutters in 1665. They mostly polished over the natural faces, covered flaws with many small facets, and kept as much weight as possible. European cutters went further, but only so far.\n\n## The old single cut\n\nThe single cut, or eight cut, does three things to the octahedron:\n\n- The cutter grinds away the top point to make a flat **table**.\n- The cutter bevels the corners into a regular octagon.\n- Every crown facet matches every other, and every pavilion facet matches every other.\n\nThat gives **8 facets above the girdle, 18 in all** (table, 8 crown facets, 8 pavilion facets and a culet). Our model adds 8 small facets at the girdle, for 26. The plan never quite disappeared: cutters still use it today for very small melee stones.\n\n### Try it yourself\n\n1. Open [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel) with `?cut=old-single&stone=diamond`. The comparison cut is the [T73](https://digitalgemology.com/cuts/t73-round-brilliant) by default, our benchmark, built on [Tolkowsky's 1919 cut](https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919). Read brilliance, fire and scintillation for both.\n2. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with `?cut=old-single&stone=diamond`. Set **Turn** to Slow and lighting to **Club**. Count the facets that you can see flash.\n3. Change the cut to the T73 round brilliant, with the same lighting. What changes: the size of the flashes, or the number?\n\n## What the Wheel and the simulator show\n\n**The scoreboard.** The [old single](https://digitalgemology.com/cuts/old-single) scores **72** for brilliance, **84** for fire and **44** for scintillation. The T73 scores 93, 78 and 80. This old cut beats the modern benchmark on fire, and loses badly on the other two.\n\n**Why so much fire?** Our fire score is a share of the light that comes back to you, not of all the light that goes in. A stone with eight big crown facets sends that light out in a few large beams. Each beam has room to spread into separate colors. So when the old single does return light, a lot of it arrives as color. That's why the simulator shows a few big, slow, colored flashes under Club lighting.\n\n**Why so little sparkle?** Scintillation is the on-and-off twinkle when you move the stone. The Wheel counts it from the number of facets that reach the surface: 26 facets give 44, and the T73's 73 give 80. Few facets, few sparkles.\n\n**Where the light goes.** In our ray census, 19% of the light leaks out through the pavilion, against 2% in the T73. Much of the missing brilliance goes there.\n\n**One caution.** These are scores for our model: a regular single cut at fixed angles (pavilion 48.5°, depth 67.5%). A real stone from the 1400s followed its crystal and was rarely this regular. The written sources say these early cuts showed little fire, and in paintings of the period table-cut diamonds look almost black. Our model shows what the plan could do, cut perfectly.\n\n## Key points\n\n- In the 1400s, the only way to shape diamond was to grind it with diamond powder on a wheel. Polishers in Nuremberg formed a guild by 1375.\n- Around 1476, Van Berquem in Bruges made strict symmetry the standard and may have improved the wheel.\n- The old single cut flattens the octahedron into a table and bevels it to an octagon: 8 facets above the girdle, 18 in all.\n- On our Wheel it has the most fire (84) and the least scintillation (44) of the eight cuts in [the history of the brilliant](https://digitalgemology.com/learn/historic-cuts). 19% of its light leaks out.\n- Fire is a share of the light that returns. Scintillation is a count of facets.\n\n**Go further:** the [old single cut page](https://digitalgemology.com/cuts/old-single) has the full diagram and proportions.\n\n## Try it free\n\n- [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel): Compare brilliance, fire and scintillation of two cuts, or one cut in two stones.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/the-old-single-eight-facets-and-a-lot-of-fire)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [Old Single Cut](https://digitalgemology.com/cuts/old-single): 3D files and cutting files, €9.99 each\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: The Mazarin cut: the first brilliant](https://digitalgemology.com/learn/historic-cuts/mazarin-cut-diamond)\n- [Try another topic · The bow-tie effect: Fixing a bow-tie: the steep belly of DG-Bowtie](https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie)\n\n[Historic diamond cuts: the history of the brilliant: all lessons](https://digitalgemology.com/learn/historic-cuts) · [All topics](https://digitalgemology.com/learn)"},{"id":"HB-L2","course":"The history of the brilliant","lesson_number":2,"title":"The Mazarin cut: the first brilliant","url":"https://digitalgemology.com/learn/historic-cuts/mazarin-cut-diamond","path":"/learn/historic-cuts/mazarin-cut-diamond","markdown":"https://digitalgemology.com/learn/historic-cuts/mazarin-cut-diamond.md","summary":"The Mazarin cut, or double cut, was the first brilliant (mid-1600s): 34 facets on a cushion outline. Why twice the facets gave less light.","queries":["mazarin cut","mazarin cut diamond","first brilliant cut"],"quiz":"https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/the-mazarin-the-first-brilliant","tools":["https://digitalgemology.com/tools/cut-performance-wheel","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/mazarin","https://digitalgemology.com/cuts/old-single"],"text":"[Historic diamond cuts: the history of the brilliant](https://digitalgemology.com/learn/historic-cuts) · 3 min read\n\n# The Mazarin cut: the first brilliant\n\nThe Mazarin, or double cut, was the first brilliant, of the mid-1600s: 16 crown facets plus the table, 34 facets in all, on a cushion outline. On our Wheel it twinkles more than the old single (scintillation 61 vs 44) but returns less light (brilliance 65 vs 72).\n\nVideo: [The old single and the Mazarin turning side by side](https://www.youtube.com/watch?v=wisPk29mNxY)\n\nThe old single and the Mazarin turning side by side, same light, at true size. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nThe old single and the Mazarin turning side by side, same light, at true size.\n\n## Two hundred years later\n\nThe [old single cut](https://digitalgemology.com/learn/historic-cuts/old-single-cut-diamond) was still in use in the 1600s, but cutters had tried new things. The question had changed: not only how to save weight, but how to make the stone come alive.\n\nThe first popular answer was not a brilliant at all.\n\n## The rose: lots of facets, no fire\n\nFrom the middle of the 1500s, the **rose cut** spread fast. It is a dome of triangular facets with a flat base: all crown, no pavilion. It suited flat pieces of rough, and it lost very little weight. For about a century it was the fashion.\n\nTolkowsky, in 1919, explained why it had to fail. In a rose, light enters through one sloping facet and leaves through another, and it meets both at the same angle. Every color bends by the same amount on the way in and on the way out. So the colors leave parallel and recombine into white. A rose can be bright, but it has almost no fire.\n\nTo make fire, light must enter through the top, reflect off a back, and leave again at a different angle. For that you need a crown on top of a pavilion: a brilliant.\n\n## The technology: still just the wheel\n\nThe tools hadn't changed since the [old single](https://digitalgemology.com/cuts/old-single): diamond powder on a wheel, set by hand. What was missing was a way to make a stone **round**. Rounding a diamond is called **bruting**: you grind its outline against another diamond. Nobody could yet do it well enough to make a true circle. So the early brilliants were all cushions, rounded squares, and so were the [Peruzzi](https://digitalgemology.com/learn/historic-cuts/peruzzi-cut-diamond) and the [old mine](https://digitalgemology.com/learn/historic-cuts/old-mine-cut-diamond) that followed.\n\n## The Mazarin, or double cut\n\nIn the middle of the 1600s, the first brilliants appeared, by tradition under the influence of Cardinal Mazarin of France. They were called **Mazarins**, or double-cut brilliants:\n\n- **16 facets above the girdle**, plus the table, twice the old single's eight.\n- **34 facets in all**: table, 16 crown facets, 16 pavilion facets and a culet. Our model adds 8 small girdle facets, for 42.\n- A wide, open culet at the bottom and a cushion outline.\n\nIt is the step between the single cut and the Peruzzi. We rebuilt our model from the drawing in Tolkowsky's *Diamond Design*.\n\n### Try it yourself\n\n1. Open [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel) with `?cut=mazarin&stone=diamond`. Set the comparison cut to the old single. Read the three scores for both.\n2. Set the comparison cut back to the [T73](https://digitalgemology.com/cuts/t73-round-brilliant), our modern benchmark.\n3. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with `?cut=mazarin&stone=diamond`, **Turn** on Slow, lighting **Sunny day**. Then change to the old single. Which one twinkles more as it turns? Which one looks brighter in the middle?\n\n## What the Wheel shows\n\n**More sparkle.** Scintillation goes from **44** to **61**. That's the facet count at work: 42 facets instead of 26.\n\n**Less light, less fire.** Brilliance drops from **72** to **65**, and fire from **84** to **63**. Twice the facets, and the stone got darker and less colorful. Against the T73 (93 / 78 / 80), the [Mazarin](https://digitalgemology.com/cuts/mazarin) is behind on all three.\n\n**Why?** Smaller facets break the light into smaller beams. Each beam has less room to spread into color, so fire falls. And nobody calculated the angles. They were whatever worked on a cushion of rough. Our model has a shallow crown (31.4°), a steep pavilion (44.3°) and a deep stone (68.8% of its width), and 17% of the light leaks out. More facets change the pattern of light. They don't fix where the light goes.\n\n**Still a big step.** Tolkowsky calls the Mazarin's fire and brilliance incomparably better than the rose's. The brilliant plan had arrived; the proportions hadn't.\n\n## Key points\n\n- The rose cut (mid-1500s) saved weight but showed almost no fire. Light leaves at the same angle it enters, so the colors recombine.\n- The Mazarin, or double cut (mid-1600s), was the first brilliant: 16 facets above the girdle, 34 in all, on a cushion outline.\n- Brilliants stayed square because nobody could yet round a diamond accurately.\n- On our Wheel, the Mazarin gains scintillation over the old single (61 vs 44) but loses brilliance (65 vs 72) and fire (63 vs 84).\n- More facets change the sparkle. Only better angles change how much light comes back.\n\n**Go further:** the [Mazarin cut page](https://digitalgemology.com/cuts/mazarin) has the diagram rebuilt from Tolkowsky's book.\n\n## Try it free\n\n- [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel): Compare brilliance, fire and scintillation of two cuts, or one cut in two stones.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/the-mazarin-the-first-brilliant)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [Mazarin Cut](https://digitalgemology.com/cuts/mazarin): 3D files and cutting files, €9.99 each\n- [Old Single Cut](https://digitalgemology.com/cuts/old-single): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: The Peruzzi cut: today's crown arriving early](https://digitalgemology.com/learn/historic-cuts/peruzzi-cut-diamond)\n- [Try another topic · Diamond anatomy and proportions: The diamond culet: none, pointed or large](https://digitalgemology.com/learn/diamond-anatomy/diamond-culet)\n\n[Previous lesson](https://digitalgemology.com/learn/historic-cuts/old-single-cut-diamond) · [Historic diamond cuts: the history of the brilliant: all lessons](https://digitalgemology.com/learn/historic-cuts) · [All topics](https://digitalgemology.com/learn)"},{"id":"HB-L3","course":"The history of the brilliant","lesson_number":3,"title":"The Peruzzi cut: today's crown arriving early","url":"https://digitalgemology.com/learn/historic-cuts/peruzzi-cut-diamond","path":"/learn/historic-cuts/peruzzi-cut-diamond","markdown":"https://digitalgemology.com/learn/historic-cuts/peruzzi-cut-diamond.md","summary":"The Peruzzi cut, or triple cut, of the late 1600s: the first 32-facet crown, still on every modern round, and why the stone still looked dull.","queries":["peruzzi cut","peruzzi cut diamond","triple cut brilliant"],"quiz":"https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/the-peruzzi-todays-crown-arriving-early","tools":["https://digitalgemology.com/tools/cut-performance-wheel","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/peruzzi","https://digitalgemology.com/cuts/mazarin","https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Historic diamond cuts: the history of the brilliant](https://digitalgemology.com/learn/historic-cuts) · 3 min read\n\n# The Peruzzi cut: today's crown arriving early\n\nThe Peruzzi, or triple cut, was made by the Venetian polisher Vincent Peruzzi toward the end of the 1600s. It doubled the crown to 32 facets (8 bezels, 8 stars, 16 upper girdle halves), the crown of every modern round, for 58 facets in all.\n\n## Doubling again\n\nThe [Mazarin](https://digitalgemology.com/learn/historic-cuts/mazarin-cut-diamond) gave cutters a crown of 16 facets. Toward the end of the 1600s, a Venetian polisher, Vincent Peruzzi, doubled it again. The cut is called the [Peruzzi](https://digitalgemology.com/cuts/peruzzi), or the **triple cut**. With it, the modern facet plan arrives.\n\n## The technology: the same tools, more skill\n\nNothing new on the bench. Diamond powder, a polishing wheel, a stone held by hand, and an outline that still couldn't be made round. What changed was ambition. Cutters now laid out 32 small facets on the crown and made them meet. That is a feat of hand and eye, with no machine to set the angles.\n\n## The modern crown, three hundred years early\n\nLook at the crown of any round brilliant today. You'll find:\n\n- **8 bezels**, the large kite-shaped facets around the table;\n- **8 stars**, the small triangles touching the table;\n- **16 upper girdle halves**, the triangles along the girdle.\n\nThat's **32 facets above the girdle**, the Peruzzi's crown. Add the table, a pavilion of 24 facets and a culet, and you get **58 facets in all**. Our model adds 16 small girdle facets, for 74.\n\nWhat the Peruzzi doesn't have is a modern shape. It is a cushion, cut deep. Our model is 69.1% as deep as it is wide, with a steep pavilion of 46.2°.\n\n![The T73 and the Peruzzi face up with their facet edges drawn.](https://digitalgemology.com/img/learn/hb-l3-t73-vs-peruzzi-face-up-mesh.webp?v=5ca5f32d)\n\nThe T73 and the Peruzzi face up with their facet edges drawn.\n\n### Try it yourself\n\n1. Open [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel) with `?cut=peruzzi&stone=diamond`. Set the comparison cut to the [Mazarin](https://digitalgemology.com/cuts/mazarin). Read brilliance, fire and scintillation for both.\n2. Set the comparison cut to the [T73](https://digitalgemology.com/cuts/t73-round-brilliant), our modern benchmark. Now read the **Symmetry** row as well.\n3. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with `?cut=peruzzi&stone=diamond`, lighting **Sunny day**, **Turn** on Slow. Watch the corners of the cushion, then the straight sides. Do they flash at the same moments?\n\n## What the Wheel and the simulator show\n\n**A step up on all three.** Against the Mazarin, the Peruzzi gains on every score: brilliance **65 → 75**, fire **63 → 68**, scintillation **61 → 81**. Tolkowsky agreed: the triple cut raised fire and brilliance a great deal.\n\n**Scintillation level with today, with a catch.** The Peruzzi scores 81, one point above the T73's 80. That's the facet count again: our Peruzzi has 74 facets and the T73 has 73. The catch is the girdle. A faceted girdle is a modern habit. A girdle can be frosted, polished smooth or faceted, and most have been faceted only in recent decades. Our model carries 16 girdle facets anyway. On a plain girdle, its 58 facets would score **72** by the Wheel's own formula, level with [Tolkowsky's T57](https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919). So the modern crown plan was there in the 1690s. The extra twinkle of a faceted girdle came much later.\n\n**But still dull.** Brilliance 75 is well behind the T73's 93, and 19% of the light leaks out, against 2%. Tolkowsky gave two reasons, and you can see both:\n\n- **Too thick.** In a deep stone with a steep pavilion, light finds its way out of the back.\n- **Corners and sides at different angles.** On a cushion, the facets at the corners and the facets along the sides can't all sit at the same angle. Even if one set is right, the other is too steep. The Wheel shows this as a **Symmetry** score of 85 against 100, and lists it as \"a less regular pavilion\". It's also why, in the simulator, the corners and the sides don't light up together as the stone turns.\n\nSeen today, Tolkowsky wrote, these stones look exceedingly dull next to modern ones. The facet plan was right. The shape wasn't, and the technology set that limit.\n\n## Key points\n\n- The Peruzzi, or triple cut (late 1600s), doubles the crown to 32 facets: 8 bezels, 8 stars, 16 upper halves. This is the crown of every modern round.\n- 58 facets in all, still on a deep cushion, still cut entirely by hand.\n- On our Wheel it improves on the Mazarin in brilliance, fire and scintillation (75 / 68 / 81).\n- Our model's scintillation matches the T73's because it carries as many facets. That includes 16 girdle facets that a stone of the 1690s wouldn't have had. On a plain girdle it would score 72.\n- It stays dull for two reasons: it is thick, and a cushion forces different angles at the corners and sides (symmetry 85). 19% of the light leaks.\n\n**Go further:** the [Peruzzi cut page](https://digitalgemology.com/cuts/peruzzi) has the facet diagram to compare with the T73's.\n\n## Try it free\n\n- [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel): Compare brilliance, fire and scintillation of two cuts, or one cut in two stones.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/the-peruzzi-todays-crown-arriving-early)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [Peruzzi Cut](https://digitalgemology.com/cuts/peruzzi): 3D files and cutting files, €9.99 each\n- [Mazarin Cut](https://digitalgemology.com/cuts/mazarin): 3D files and cutting files, €9.99 each\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Old mine cut diamonds: tidier, not brighter](https://digitalgemology.com/learn/historic-cuts/old-mine-cut-diamond)\n- [Try another topic · Diamond anatomy and proportions: The diamond culet: none, pointed or large](https://digitalgemology.com/learn/diamond-anatomy/diamond-culet)\n\n[Previous lesson](https://digitalgemology.com/learn/historic-cuts/mazarin-cut-diamond) · [Historic diamond cuts: the history of the brilliant: all lessons](https://digitalgemology.com/learn/historic-cuts) · [All topics](https://digitalgemology.com/learn)"},{"id":"HB-L4","course":"The history of the brilliant","lesson_number":4,"title":"Old mine cut diamonds: tidier, not brighter","url":"https://digitalgemology.com/learn/historic-cuts/old-mine-cut-diamond","path":"/learn/historic-cuts/old-mine-cut-diamond","markdown":"https://digitalgemology.com/learn/historic-cuts/old-mine-cut-diamond.md","summary":"Old mine cut diamonds (1700s and 1800s): the Peruzzi's 58 facets made neater and rounder by hand. Why the tidier stone returned less light.","queries":["old mine cut diamond","old mine cut vs old european","antique cushion cut"],"quiz":"https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/the-old-mine-tidier-not-brighter","tools":["https://digitalgemology.com/tools/cut-performance-wheel","https://digitalgemology.com/tools/brightness-tilt-analysis","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/old-mine","https://digitalgemology.com/cuts/peruzzi","https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Historic diamond cuts: the history of the brilliant](https://digitalgemology.com/learn/historic-cuts) · 3 min read\n\n# Old mine cut diamonds: tidier, not brighter\n\nAn old mine cut is an antique cushion-shaped diamond of the 1700s and 1800s: the Peruzzi's 58 facets, made more uniform and rounder by hand. On our Wheel it is the darkest of the historic cuts: brilliance 59, with 32% of the light leaking out.\n\nVideo: [The old mine against the T73 across the tilt](https://www.youtube.com/watch?v=Ecse__YBzZA)\n\nThe old mine against the T73 across the tilt, in the Brightness & Tilt Analysis. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nThe old mine against the T73 across the tilt, in the Brightness & Tilt Analysis.\n\n## A new source of rough\n\nFor centuries, almost every diamond came from India. In the 1720s that changed: large deposits were found in Brazil. (Tolkowsky gives 1728, other sources 1725.) More rough reached Europe's cutting centers.\n\nThe trade now calls the antique stones from this period **[old mine](https://digitalgemology.com/cuts/old-mine) cuts**. The name comes from the old mines of India and Brazil.\n\n## The technology: refinement by hand\n\nThere was still no machine to round a diamond. What improved over the 1700s and 1800s was handwork. In Tolkowsky's words, cutters modified the old-cut brilliants: they made the size and angle of the facets more uniform. That produced \"a somewhat rounder stone\".\n\nSo the old mine cut is the [Peruzzi](https://digitalgemology.com/learn/historic-cuts/peruzzi-cut-diamond) tidied up:\n\n- **the same 58 facets**, in the same plan (our model again adds 16 girdle facets, for 74);\n- facets more even in size and angle;\n- a rounder cushion, with a wider table (60.3% of the width in our model) and a shallower stone (65.6% deep, against the [Peruzzi](https://digitalgemology.com/cuts/peruzzi)'s 69.1%).\n\nOn paper, every one of those changes sounds like progress.\n\n![The Peruzzi and the old mine face up, edges drawn, at true size: the rounder outline and wider table.](https://digitalgemology.com/img/learn/hb-l4-peruzzi-vs-old-mine-face-up-mesh.webp?v=2a65e446)\n\nThe Peruzzi and the old mine face up, edges drawn, at true size: the rounder outline and wider table.\n\n### Try it yourself\n\n1. Open [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel) with `?cut=old-mine&stone=diamond`. Set the comparison cut to the Peruzzi. Read brilliance, fire, scintillation and symmetry for both.\n2. Before you look: which one do you expect to be brighter?\n3. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with `?cut=old-mine&stone=diamond` and open the **Light Return** view. Then change to the Peruzzi. Where are the dark areas in each?\n\n## What the Wheel shows\n\n**Neater.** Symmetry goes up from **85** to **90**: the more uniform facets show.\n\n**Darker.** Brilliance drops from **75** to **59**. That is the lowest of all eight cuts in [the history of the brilliant](https://digitalgemology.com/learn/historic-cuts), and our [old mine cut page](https://digitalgemology.com/cuts/old-mine) agrees: the least light face-up of the antique cuts. In our ray census, **32%** of the light leaks out. That is the most of any historic diamond cut we measure, against the Peruzzi's 19% and the [T73](https://digitalgemology.com/cuts/t73-round-brilliant)'s 2%.\n\n**The rest barely moves.** Fire goes from 68 to 72. Scintillation stays at **81**, because the facet count stays at 74.\n\n**Why would a tidier stone be darker?** Because nobody was aiming at light. Cutters wanted a neat, even stone that kept as much weight as possible. The angles followed the rough and the habit of the workshop. Our model's steep pavilion (44.4°) and wide table are one plausible version of that. Tidy facets and a rounder outline are craftsmanship. Whether light comes back is optics, and in the 1700s nobody had worked out the optics.\n\n**And yet people love them.** Old mine stones have a soft, chunky, candlelit look, with big flashes and dark areas between them. That's partly what the numbers measure: less light that comes straight back to your eye. Whether it's a fault is taste. Our Wheel measures light, not charm.\n\n## Key points\n\n- Brazil's deposits, found in the 1720s, ended India's near-monopoly on diamond.\n- The old mine cut is the Peruzzi made more uniform and rounder, by hand: same 58 facets, wider table, shallower stone.\n- On our Wheel, symmetry improves (85 → 90) but brilliance falls (75 → 59), the lowest of all the historic cuts.\n- It leaks 32% of the light, the most of any historic diamond cut we measure.\n- Neatness and weight were the goals. Nobody calculated the angles yet.\n\n**Go further:** the [old mine cut page](https://digitalgemology.com/cuts/old-mine) has the 3D model and cutting file, if you want an antique-style stone for a reproduction piece.\n\n## Try it free\n\n- [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel): Compare brilliance, fire and scintillation of two cuts, or one cut in two stones.\n- [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis): Face-up brightness under four standard lights, and how it holds as the stone tilts.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/the-old-mine-tidier-not-brighter)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [Old Mine Cut](https://digitalgemology.com/cuts/old-mine): 3D files and cutting files, €9.99 each\n- [Peruzzi Cut](https://digitalgemology.com/cuts/peruzzi): 3D files and cutting files, €9.99 each\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Old European cut diamonds: when the outline went round](https://digitalgemology.com/learn/historic-cuts/old-european-cut-diamond)\n- [Try another topic · The bow-tie effect: Fixing a bow-tie: the steep belly of DG-Bowtie](https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie)\n\n[Previous lesson](https://digitalgemology.com/learn/historic-cuts/peruzzi-cut-diamond) · [Historic diamond cuts: the history of the brilliant: all lessons](https://digitalgemology.com/learn/historic-cuts) · [All topics](https://digitalgemology.com/learn)"},{"id":"HB-L5","course":"The history of the brilliant","lesson_number":5,"title":"Old European cut diamonds: when the outline went round","url":"https://digitalgemology.com/learn/historic-cuts/old-european-cut-diamond","path":"/learn/historic-cuts/old-european-cut-diamond","markdown":"https://digitalgemology.com/learn/historic-cuts/old-european-cut-diamond.md","summary":"Old European cut diamonds: the bruting machine made the outline round. Same 58 facets, brilliance 59 to 90, and how it compares with a modern round.","queries":["old european cut diamond","old european cut vs round brilliant","old european cut sparkle"],"quiz":"https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/the-old-european-when-the-outline-went-round","tools":["https://digitalgemology.com/tools/cut-performance-wheel","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/old-european","https://digitalgemology.com/cuts/old-mine","https://digitalgemology.com/cuts/t73-round-brilliant","https://digitalgemology.com/cuts/peruzzi"],"text":"[Historic diamond cuts: the history of the brilliant](https://digitalgemology.com/learn/historic-cuts) · 3 min read\n\n# Old European cut diamonds: when the outline went round\n\nThe old European cut, the standard round from the 1870s to about 1930, keeps the old mine's 58 facets on a round outline made by the bruting machine. On our Wheel that lifts brilliance from 59 to 90 and cuts leakage from 32% to 5%.\n\nVideo: [The old mine and the old European turning side by side](https://www.youtube.com/watch?v=uuwMChztwyk)\n\nThe old mine and the old European turning side by side at the same carat weight and true size, the old European brighter in the center. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nThe old mine and the old European turning side by side at the same carat weight and true size, the old European brighter in the center.\n\n## Two hundred years of cushions\n\nSince the [Mazarin](https://digitalgemology.com/learn/historic-cuts/mazarin-cut-diamond), every brilliant had been a cushion. Not by choice. To round a diamond, you grind its outline against another diamond. This is called **bruting**, and by hand nobody could do it accurately. Careful handwork had already made the [old mine cut](https://digitalgemology.com/learn/historic-cuts/old-mine-cut-diamond) rounder and neater, and it got darker.\n\nIn the 1870s, a machine finished the job.\n\n## The technology: the bruting machine\n\nTwo things arrived together in the second half of the 1800s.\n\n**A machine.** In Boston, the jeweler Henry Morse opened a diamond-cutting workshop around 1860. His foreman, Charles Field, built a mechanical bruting machine to replace rounding by hand. The two also brought dimensional gauges into the trade, so a cutter could measure a stone and not judge it by eye. Tolkowsky thought mechanical bruting more likely started in Amsterdam or Antwerp, where nearly all diamonds were cut. Either way, by the 1870s a cutter could make a diamond truly round.\n\n**More rough.** In 1866 the first diamond was found in South Africa. Within a few years the Kimberley mines produced diamonds on a scale the world had never seen. With plenty of rough, cutters could afford to give up weight for beauty. Morse is remembered for exactly that bet: a smaller stone that looks better sells better.\n\n## Why round matters\n\nOn a cushion, the facets at the corners and those along the sides can't sit at the same angle, as [the Peruzzi](https://digitalgemology.com/learn/historic-cuts/peruzzi-cut-diamond) shows. On a circle, they can. The cutter can give every pavilion main one angle. Once that angle is right everywhere, the stone no longer needs to be thick. Tolkowsky describes it this way: as the corners shrank in, the stones could be cut less thick, with more fire and life.\n\nThat's the **[old European](https://digitalgemology.com/cuts/old-european) cut**:\n\n- **the same 58 facets** as the [Peruzzi](https://digitalgemology.com/cuts/peruzzi) and the [old mine](https://digitalgemology.com/cuts/old-mine): nothing added (our model again adds 16 girdle facets, for 74);\n- a **round** outline;\n- a thinner stone (64.7% deep in our model, against the old mine's 65.6% and the Peruzzi's 69.1%), with a small table (45%), a crown of 35.0° and a pavilion of 41.5°.\n\nIt became the standard round and stayed on the market until about 1930. Most antique round diamonds you'll find are old Europeans.\n\n### Try it yourself\n\n1. Open [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel) with `?cut=old-european&stone=diamond`. Set the comparison cut to the old mine. Read brilliance, fire and scintillation.\n2. Set the comparison cut to the [T73](https://digitalgemology.com/cuts/t73-round-brilliant), our modern benchmark. Read the **Global** row too.\n3. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with `?cut=old-european&stone=diamond`, lighting **Sunny day**. Then change to the old mine. Where did the dark areas go?\n\n## What the Wheel shows\n\n**The biggest jump on our scoreboard.** Brilliance goes from **59** to **90**: 31 points, with the same facets. Leakage drops from **32%** to **5%**. Against the Peruzzi, the 58-facet cut it comes from, leakage falls from 19% to 5%.\n\n**Fire and sparkle hold.** Fire rises a little, **72 → 74**. Scintillation stays at **81**: same facets, same count.\n\n**Close to modern.** Against the T73, the old European is 90 / 74 / 81 against 93 / 78 / 80. On the Wheel's Global score, it's 88 against 90: within two points of the modern benchmark.\n\n**What about \"more fire than a modern round\"?** You'll often read that old Europeans have more fire than modern brilliants. Our model doesn't show it: 74 against the T73's 78. The small table does make large, slow flashes, and people may mean those. But measured as a share of returned light, the modern round comes out ahead. Try it in the simulator under Club lighting and judge for yourself.\n\n**The main point.** No new facets. No new plan. A machine made the outline round, and with it came a single, correct pavilion angle all the way around. Technology, not decoration, closed the gap.\n\n## Key points\n\n- Mechanical bruting (1870s) made diamonds truly round for the first time. Dimensional gauges arrived with it.\n- South Africa's mines (from 1866) gave plenty of rough, so cutters could trade weight for beauty.\n- On a round outline, every pavilion main can share one angle, so the cutter can make the stone thinner.\n- The old European keeps the same 58 facets. Against the old mine, brilliance goes 59 → 90 and leakage 32% → 5%: the biggest jump on our [scoreboard of eight cuts](https://digitalgemology.com/learn/historic-cuts/beyond-the-tolkowsky-brilliant#the-whole-story-in-one-table).\n- It ends within two points of the T73 on the Wheel's Global score (88 vs 90). Its fire (74) is below the T73's (78) in our model.\n\n**Go further:** the [old European cut page](https://digitalgemology.com/cuts/old-european) has the diagram, the 3D model and the cutting file for antique-style work.\n\n## Try it free\n\n- [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel): Compare brilliance, fire and scintillation of two cuts, or one cut in two stones.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/the-old-european-when-the-outline-went-round)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [Old European Cut](https://digitalgemology.com/cuts/old-european): 3D files and cutting files, €9.99 each\n- [Old Mine Cut](https://digitalgemology.com/cuts/old-mine): 3D files and cutting files, €9.99 each\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n- [Peruzzi Cut](https://digitalgemology.com/cuts/peruzzi): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Tolkowsky's 1919 ideal cut: the brilliant that was calculated](https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919)\n- [Try another topic · The bow-tie effect: Fixing a bow-tie: the steep belly of DG-Bowtie](https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie)\n\n[Previous lesson](https://digitalgemology.com/learn/historic-cuts/old-mine-cut-diamond) · [Historic diamond cuts: the history of the brilliant: all lessons](https://digitalgemology.com/learn/historic-cuts) · [All topics](https://digitalgemology.com/learn)"},{"id":"HB-L6","course":"The history of the brilliant","lesson_number":6,"title":"Tolkowsky's 1919 ideal cut: the brilliant that was calculated","url":"https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919","path":"/learn/historic-cuts/tolkowsky-ideal-cut-1919","markdown":"https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919.md","summary":"Tolkowsky's 1919 ideal cut: how he calculated the pavilion (40.75°), crown (34.5°) and table (53%) from diamond's refractive index, and what he left out.","queries":["tolkowsky ideal cut","marcel tolkowsky diamond design","tolkowsky proportions"],"quiz":"https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/tolkowsky-1919-the-cut-that-was-calculated","tools":["https://digitalgemology.com/tools/cut-performance-wheel","https://digitalgemology.com/tools/brightness-tilt-analysis","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/t57-round-brilliant","https://digitalgemology.com/cuts/t73-round-brilliant","https://digitalgemology.com/cuts/old-european"],"text":"[Historic diamond cuts: the history of the brilliant](https://digitalgemology.com/learn/historic-cuts) · 5 min read\n\n# Tolkowsky's 1919 ideal cut: the brilliant that was calculated\n\nMarcel Tolkowsky's 1919 ideal cut was calculated, not found by trial and error. From diamond's refractive index (2.417) and critical angle (24° 26′), he set a pavilion angle of 40.75°, a crown angle of 34.5° and a table of 53%.\n\nVideo: [Tolkowsky's 1919 ideal cut: the math behind the round brilliant (animated)](https://www.youtube.com/watch?v=nQ4ikoPq_u8)\n\nTolkowsky's 1919 calculation, in 2D. The critical angle comes from diamond's refractive index, 2.417. A vertical ray meets the pavilion at a, the opposite facet at 180° − 3a and the top at 180° − 4a. His brilliancy rule puts the exit at 45°, which gives a = 40° 45′. · 1 min 24 s · No sound, captions on screen\n\n## Transcript\n\nTolkowsky started from one number: the refractive index of diamond, 2.417.\n\nFrom it, he calculated the critical angle of diamond: 24° 26′, or 24.4°.\n\nPast that angle from the perpendicular, a facet reflects all the light inside.\n\nHe worked on a 2D slice: a flat top and two pavilion facets at an angle, a.\n\nA ray comes straight down. It meets the first facet at the pavilion angle, a.\n\nIt reflects to the opposite facet, and meets it at 180° − 3a.\n\nThen it meets the top at 180° − 4a. Under 24.4°, it gets out.\n\nAt 40.75°, the three angles are 40.75°, 57.75° and 17.0°. All three pass.\n\nChange the pavilion angle, and the ray still comes back up. Its exit angle changes.\n\nSo Tolkowsky needed one more rule to fix the angle. It was about fire.\n\nHis rule: a bigger exit angle spreads the colors more, but lets less light out.\n\nHe took their product as brilliancy. It is largest at an exit angle of 45°.\n\nTo leave at 45°, the ray must meet the top at 17.0°.\n\nSo 180° − 4a = 17°. That gives a pavilion angle of 40.75°, or 40° 45′.\n\nHis view: a steeper pavilion would reflect better, but not make up for the lost fire.\n\nHe set the crown by the same rule: a balance of brilliance and fire.\n\nHis 1919 numbers: pavilion 40° 45′, crown 34° 30′, table 53%.\n\nHis model was a 2D slice, with light from straight above and at most two reflections.\n\nThen he measured well-cut stones of his day. They were strikingly close to his numbers.\n\n## Five hundred years of trial and error\n\nEvery cut before 1919 came from trying: a [better wheel](https://digitalgemology.com/learn/historic-cuts/old-single-cut-diamond), a [new facet plan](https://digitalgemology.com/learn/historic-cuts/mazarin-cut-diamond), a [machine that rounds](https://digitalgemology.com/learn/historic-cuts/old-european-cut-diamond). Nobody had calculated what shape a diamond *should* be. In 1919, Marcel Tolkowsky, an engineer from a family of diamond cutters, opened his book *Diamond Design* with that point. The art, he wrote, had progressed entirely by trial and error. His aim was to calculate the best shape.\n\n## The technology: the saw, and mathematics\n\n**The saw.** Around 1900, inventors patented motorized rotary saws for diamond (1901 and 1902). Until then a cutter could only split a rough along its cleavage planes or grind it away. A saw could cut a stone wherever the cutter chose, even across the grain. So two stones could come out of one octahedron, with less waste. The saw and good lathes for bruting made it practical to cut every stone to the same round plan. So the crystal did not have to decide the shape.\n\n**Mathematics.** Tolkowsky's tools were geometry, trigonometry and one number: diamond's refractive index, 2.417. From it he calculated diamond's critical angle, **24° 26′** (24.4°). When light strikes the inside of a facet at more than that angle from the perpendicular, the facet reflects all of it. At less, the light leaks out.\n\n## How he worked it out\n\nHe split the problem in two.\n\n- **The pavilion: keep the light in.** A ray that comes straight down through the table must reflect completely off one pavilion facet, then off the opposite one. Then it must go back up through the front. His calculation for this gave a pavilion angle of **40.75°**.\n- **The crown: share the light out as fire.** Steeper crown facets spread the colors further apart but let less light through. Flatter ones do the reverse. Tolkowsky set the crown where the product of the two is largest, a balance of brilliance and fire: **34.5°**, with a table of **53%**.\n\nHe then measured well-cut stones of his day and found them strikingly close to his numbers. He also noted the price: even a perfectly cut brilliant loses at least 52% of its rough.\n\n## What he left out\n\nTolkowsky worked on a **two-dimensional slice** through the stone, with light coming **straight from above**. He followed each ray for **at most two reflections**. Real light enters from every direction, and real rays bounce many times. His answer was a very good start, not the last word. Today a computer can do each of these: see [Past the 1919 ceiling: DG-Miliano and the modern brilliant](https://digitalgemology.com/learn/historic-cuts/beyond-the-tolkowsky-brilliant).\n\n## Our model: the T57\n\nOur **[T57](https://digitalgemology.com/cuts/t57-round-brilliant)** is Tolkowsky's plan as he drew it: 57 facets (table, 32 crown, 24 pavilion), no culet, and a **knife-edge girdle**, with no girdle facets at all. Crown 34.5°, pavilion 40.8°, 59.2% deep. The **[T73](https://digitalgemology.com/cuts/t73-round-brilliant)**, our benchmark on the Wheel, has the same angles plus 16 girdle facets: 73.\n\n![Tolkowsky's angles in the Cut Grading Tool's profile, crown 34.5° and pavilion 40.8° (the tool's 0.2° step for 40.75°).](https://digitalgemology.com/img/learn/hb-l6-cgt-1919-angles.webp?v=2a4574e7)\n\nTolkowsky's angles in the Cut Grading Tool's profile, crown 34.5° and pavilion 40.8° (the tool's 0.2° step for 40.75°).\n\n### Try it yourself\n\n1. Open [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel) with `?cut=t57-round-brilliant&stone=diamond`. Set the comparison cut to the [old European](https://digitalgemology.com/cuts/old-european). Read brilliance, fire and scintillation.\n2. Set the comparison cut to the T73. The angles are the same; only the girdle is different. Which score moves?\n3. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with `?cut=t57-round-brilliant&stone=diamond`, **Turn** on Slow, lighting **Sunny day**. Then load the old European. Look at the center of each stone.\n\n## What the Wheel and the simulator show\n\n**Against the old European.** The T57 scores **92** for brilliance against 90, and **79** for fire against 74. The calculation pays off most in fire. Scintillation is **72** against 81, which looks like a step back. It isn't one, as the next comparison shows.\n\nVideo: [The old European against the T73 across the tilt](https://www.youtube.com/watch?v=_VF1llXVoq8)\n\nThe old European against the T73 across the tilt, in the Brightness & Tilt Analysis. · 10 s · No sound\n\n**Against the T73.** Same crown, same pavilion, same table. Brilliance 92 vs 93, fire 79 vs 78: practically identical. Scintillation 72 vs 80. The difference is the girdle. The T73 has 16 girdle facets (and a girdle band, so it's a little deeper, 61.7% against 59.2%). The Wheel counts scintillation from the facets that reach the surface: 57 facets give 72, 73 give 80. So the knife-edge girdle, not the angles, gives the T57 its lower number. Our [old European](https://digitalgemology.com/learn/historic-cuts/old-european-cut-diamond) model has 16 girdle facets, so it gets the higher count. On a plain girdle, its 58 facets would score 72 too (faceted girdles are a recent habit: see [the Peruzzi](https://digitalgemology.com/learn/historic-cuts/peruzzi-cut-diamond)).\n\n**Where the light comes back.** In the simulator, compare the centers. The old European's table is much smaller (45% against 53%), so you see more crown facets face-up. The T57 shows you a wide, open table with the pavilion's reflections behind it.\n\n![The T57 beside the old European at true size: compare the centers.](https://digitalgemology.com/img/learn/hb-l6-t57-vs-old-european.webp?v=c5680eb9)\n\nThe T57 beside the old European at true size: compare the centers.\n\n**What Tolkowsky changed.** Not a facet, not a tool on the bench, but the method. From 1919, you could design a cut on paper from the properties of the material, before you touched a stone. Every modern round is built on his numbers.\n\n![From the old single to the T73, six cuts at 1.00 ct, at their true sizes.](https://digitalgemology.com/img/learn/hb-l6-lineup.webp?v=57b736c2)\n\nFrom the old single to the T73, six cuts at 1.00 ct, at their true sizes.\n\nVideo: [The same six turning together](https://www.youtube.com/watch?v=VfeYQ5CZakc)\n\nThe same six turning together. · 10 s · No sound\n\n## Key points\n\n- Motorized diamond saws (patented 1901 and 1902) and good lathes let cutters cut every stone to the same plan, with less waste.\n- Tolkowsky calculated his cut from diamond's refractive index (2.417) and critical angle (24° 26′):\n  - pavilion 40.75° to keep light in\n  - crown 34.5° to balance light and fire\n  - table 53%.\n- His model was a 2D slice, with light straight from above and at most two reflections.\n- On our Wheel, the T57 beats the old European in brilliance (92 vs 90) and fire (79 vs 74).\n- The T57 and T73 share the same angles. The T73's 16 girdle facets raise scintillation from 72 to 80.\n\n**Go further:** the [T57 round brilliant page](https://digitalgemology.com/cuts/t57-round-brilliant) has the 1919 plan with its knife-edge girdle, and the [T73 page](https://digitalgemology.com/cuts/t73-round-brilliant) the version with girdle facets.\n\n## Try it free\n\n- [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel): Compare brilliance, fire and scintillation of two cuts, or one cut in two stones.\n- [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis): Face-up brightness under four standard lights, and how it holds as the stone tilts.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/tolkowsky-1919-the-cut-that-was-calculated)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T57 Round Brilliant Cut](https://digitalgemology.com/cuts/t57-round-brilliant): 3D files and cutting files, €9.99 each\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n- [Old European Cut](https://digitalgemology.com/cuts/old-european): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Hearts and arrows diamonds: precision you can see](https://digitalgemology.com/learn/historic-cuts/hearts-and-arrows-diamonds)\n- [Try another topic · Diamond anatomy and proportions: Crown angle and crown height in a round diamond](https://digitalgemology.com/learn/diamond-anatomy/diamond-crown-angle)\n\n[Previous lesson](https://digitalgemology.com/learn/historic-cuts/old-european-cut-diamond) · [Historic diamond cuts: the history of the brilliant: all lessons](https://digitalgemology.com/learn/historic-cuts) · [All topics](https://digitalgemology.com/learn)"},{"id":"HB-L7","course":"The history of the brilliant","lesson_number":7,"title":"Hearts and arrows diamonds: precision you can see","url":"https://digitalgemology.com/learn/historic-cuts/hearts-and-arrows-diamonds","path":"/learn/historic-cuts/hearts-and-arrows-diamonds","markdown":"https://digitalgemology.com/learn/historic-cuts/hearts-and-arrows-diamonds.md","summary":"Hearts and arrows diamonds: where the pattern came from (1985 to 1988), how a viewer shows it, and why it proves symmetry, not light return.","queries":["hearts and arrows diamond","hearts and arrows viewer","are hearts and arrows worth it"],"quiz":"https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/hearts-and-arrows-precision-you-can-see","tools":["https://digitalgemology.com/tools/hearts-and-arrows-scope","https://digitalgemology.com/tools/cut-performance-wheel"],"cuts":["https://digitalgemology.com/cuts/t73-round-brilliant","https://digitalgemology.com/cuts/t57-round-brilliant","https://digitalgemology.com/cuts/dg-broken-hearts-and-arrows"],"text":"[Historic diamond cuts: the history of the brilliant](https://digitalgemology.com/learn/historic-cuts) · 6 min read\n\n# Hearts and arrows diamonds: precision you can see\n\nA hearts and arrows diamond shows eight arrows face-up and eight hearts face-down in a reflector viewer. The pattern appears only when opposite facets match in angle and direction in 3D, so it shows the cutter's precision, not how much light the stone returns.\n\nVideo: [The T73 in the Hearts & Arrows Scope](https://www.youtube.com/watch?v=y7Lw8n9l0CM)\n\nThe T73 in the Hearts & Arrows Scope, arrows face up, turned over to the hearts. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nThe T73 in the Hearts & Arrows Scope, arrows face up, turned over to the hearts.\n\n## Sixty quiet years\n\nAfter [Tolkowsky's 1919 cut](https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919), his proportions became the basis for the \"ideal cut\" standards that followed. One slow change matters here. Over the decades, the **lower girdle facets** grew longer. These are the long triangles on the pavilion, beside the mains. The pavilion mains between them grew narrower. Nobody did this to make hearts. It just happened to set the stage.\n\nThe next step didn't come from a new cutting tool. It came from a new way of **looking**.\n\n## The technology: the instrument came before the cut\n\n**Reflector viewers.** Between 1977 and 1984, Ken Shigetomi and colleagues in Japan researched a viewer that judges a cut by the light it returns. It became the **FireScope**. A Japanese utility model published in 1985 describes a similar idea: a magnifier with its own light and a red disc with a hole in the middle. In it, red reflection reads as good brilliance.\n\nJudged that way, very few stones passed. According to the EightStar account, a worldwide search through tens of thousands of diamonds found almost none that performed perfectly in the FireScope. So cutters started to cut stones *for* the viewer. The first **EightStar** was cut in Tokyo in 1985.\n\n**The name.** A first copy, called Apollon 8, followed in 1987. The company behind it failed over quality control. One of its salesmen, **Kinsaku Yamashita**, bought the remaining stones and took over the subcontractors. In 1988, he renamed the cut **Hearts and Arrows**. Japan's Zenhokyo lab tells it differently: a Mr. K. Yamashita, president of Mount Gold Co., found the pattern by accident with a cut proportion scope. Both accounts lead back to Yamashita.\n\n**The viewer, patented.** Yamashita filed a patent on his viewer in Japan in 1989 and in the US in 1990, granted in 1993 (US 5,260,763). It's a simple device. An opaque tube holds the stone over a black base. A white, semi-transparent tube above it limits the light that reaches the stone. What matters is the angle. Seen from the center of the stone, the rim of the tube should sit 10–25° off the axis, and the best patterns show at about 15–20°. A red inner wall colors the pattern. In the viewer, an ideal cut shows **eight arrows** face-up and **eight hearts** face-down; a poorly cut stone shows neither. The patent itself admits the optical principle isn't fully clear.\n\n**Into the market.** EightStar opened in the US in 1990. Hearts On Fire was founded in Boston in 1996, and by 1997 US brands sold stones as hearts and arrows. In Japan, the Central Gem Laboratory registered its own name for the pattern, \"Heart & Cupid\".\n\n## How the pattern forms\n\n- **Arrows (face-up):** the opposite pavilion main reflects each pavilion main, and that makes the shaft. The crown main adds a second view of that reflection, and that makes the arrowhead.\n- **Hearts (face-down):** six facet reflections build each heart. Four, tied to the pavilion mains, form the body. Two upper-half facets square off the top of the heart.\n\nFor all sixteen halves to match, opposite facets must line up in three dimensions: same angle *and* same direction around the stone. That's a stricter kind of symmetry than a lab's ordinary symmetry grade, which checks the facets as they sit on the surface. Small errors that you'd never see face-up break the pattern at once.\n\n**Lower halves shape the hearts.** A common rule of thumb: lower halves at about 75% or less give fatter hearts with less gap between them. At 80% or more, the hearts are thinner, with more separation.\n\n### Try it yourself\n\n1. Open [Hearts & Arrows Scope](https://digitalgemology.com/tools/hearts-and-arrows-scope) and choose the [T73](https://digitalgemology.com/cuts/t73-round-brilliant) round brilliant in diamond. Look at both views. Read the Arrows Symmetry and Hearts Symmetry numbers.\n2. Under **Symmetry**, turn up **Crown twist** a little, then **Main angles**, then **Main spacing**, one at a time. Watch which part of the pattern breaks first.\n3. Reset. Make the **Table size** much smaller, and then much larger. The Central Gem Laboratory says that a table that's too small spoils the heart shape, and one that's too large turns the hearts into a leaf shape. Does our Scope agree?\n4. Reset, and change the gemstone to moissanite. What happens to the pattern? Does the symmetry number change?\n5. Open [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel) with `?cut=t73-round-brilliant&stone=diamond`. Set the comparison cut to the [T57](https://digitalgemology.com/cuts/t57-round-brilliant), [Tolkowsky's 1919 plan](https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919).\n\n## What the Scope and the Wheel show\n\n**Precision you can see.** Tiny changes in twist, angle or spacing, far too small to see face-up, break the hearts and arrows. That's the whole value of the pattern: it turns the cutter's precision into a picture anyone can check. The Central Gem Laboratory makes the same point. Numbers can judge proportions, but symmetry was hard to judge, even for the trade. So they devised a way to judge it from the reflection image.\n\n![The crown twisted 1°: the arrows bend and symmetry drops.](https://digitalgemology.com/img/learn/hb-l7-t73-crown-twist-hearts-arrows.webp?v=14ee3594)\n\nThe crown twisted 1°: the arrows bend and symmetry drops.\n\n![The pavilion mains up to 0.2° off.](https://digitalgemology.com/img/learn/hb-l7-t73-main-angles-hearts-arrows.webp?v=230f6dbb)\n\nThe pavilion mains up to 0.2° off.\n\n**Not a light-performance test.** In moissanite, the pattern falls apart while the symmetry stays perfect. The pattern needs perfect symmetry, and also angles that suit the stone's refractive index. We bring the hearts back in [Moissanite's refractive index, and why it needs its own cut](https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-refractive-index-and-cut). We change only the pavilion and crown. The reverse holds too: the Central Gem Laboratory notes that the pattern can appear in stones whose overall cut grade is below the top. A crisp pattern says the facets match each other. Whether the crown and pavilion angles work together to bring the light back is a separate question.\n\n![The same cut in moissanite: the pattern collapses, symmetry still 100%.](https://digitalgemology.com/img/learn/hb-l7-t73-moissanite-hearts-arrows.webp?v=ee7f96d5)\n\nThe same cut in moissanite: the pattern collapses, symmetry still 100%.\n\n**On the scoreboard.** The T73 scores **93 / 78 / 80** against the T57's 92 / 79 / 72. Brilliance and fire barely move, because the angles are the same. Scintillation rises because of the 16 girdle facets. Symmetry is **100**, leakage **2%**. In our models, hearts and arrows needs no new angles: the T73 shows the pattern on Tolkowsky's own. What it demands is precision. What it gave buyers is a way to see that precision.\n\nVideo: [The Cut Performance Wheel, the T57 giving way to the T73](https://www.youtube.com/watch?v=3Y-HlQxjZug)\n\nThe Cut Performance Wheel, the T57 giving way to the T73. · 10 s · No sound\n\n**Who grades it.** There's no single standard.\n\n- In Japan, labs set their own.\n- GIA and AGS don't grade hearts and arrows. An \"H&A\" inscription on their report only means the submitter asked for it.\n- IGI and GCAL apply H&A standards.\n\n## Key points\n\n- After 1919, Tolkowsky's proportions became the basis for ideal cuts. The lower girdle facets slowly grew longer, and later this shaped the hearts.\n- The instrument came first. Reflector viewers (FireScope research 1977–1984) judged cut by returned light, and cutters began to cut stones to perform in them (EightStar, 1985).\n- Kinsaku Yamashita named the cut Hearts and Arrows (1988) and patented his viewer (US 5,260,763, granted 1993). The best patterns show at about 15–20° off the axis.\n- The pattern needs opposite facets to match in angle and direction, in 3D. That is a stricter symmetry than a lab's symmetry grade.\n- It shows precision, not light performance. The T73 scores 93 / 78 / 80 with symmetry 100, but the same stone in moissanite loses the pattern.\n\n**Go further:** our [DG-Broken Hearts and Arrows](https://digitalgemology.com/cuts/dg-broken-hearts-and-arrows) is the T73 with 16 narrow extra facets on the pavilion. They put a thin red crack in every heart, on purpose.\n\n## Try it free\n\n- [Hearts & Arrows Scope](https://digitalgemology.com/tools/hearts-and-arrows-scope): See the arrows face up and the hearts face down as you change the cut.\n- [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel): Compare brilliance, fire and scintillation of two cuts, or one cut in two stones.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/hearts-and-arrows-precision-you-can-see)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n- [T57 Round Brilliant Cut](https://digitalgemology.com/cuts/t57-round-brilliant): 3D files and cutting files, €9.99 each\n- [DG-Broken Hearts and Arrows Cut](https://digitalgemology.com/cuts/dg-broken-hearts-and-arrows): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Past the 1919 ceiling: DG-Miliano and the modern brilliant](https://digitalgemology.com/learn/historic-cuts/beyond-the-tolkowsky-brilliant)\n- [Try another topic · Diamond anatomy and proportions: The parts of a diamond: crown, girdle and pavilion](https://digitalgemology.com/learn/diamond-anatomy/parts-of-a-diamond)\n\n[Previous lesson](https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919) · [Historic diamond cuts: the history of the brilliant: all lessons](https://digitalgemology.com/learn/historic-cuts) · [All topics](https://digitalgemology.com/learn)"},{"id":"HB-L8","course":"The history of the brilliant","lesson_number":8,"title":"Past the 1919 ceiling: DG-Miliano and the modern brilliant","url":"https://digitalgemology.com/learn/historic-cuts/beyond-the-tolkowsky-brilliant","path":"/learn/historic-cuts/beyond-the-tolkowsky-brilliant","markdown":"https://digitalgemology.com/learn/historic-cuts/beyond-the-tolkowsky-brilliant.md","summary":"Which diamond cut is brightest? On our Wheel DG-Miliano scores 95 / 82 / 98 against the T73's 93 / 78 / 80. Where the gain comes from, read honestly.","queries":["brightest diamond cut","most brilliant diamond cut","modern round brilliant variations"],"quiz":"https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/dg-miliano-past-the-1919-ceiling","tools":["https://digitalgemology.com/tools/cut-performance-wheel","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/dg-miliano","https://digitalgemology.com/cuts/t73-round-brilliant"],"text":"[Historic diamond cuts: the history of the brilliant](https://digitalgemology.com/learn/historic-cuts) · 5 min read\n\n# Past the 1919 ceiling: DG-Miliano and the modern brilliant\n\nIn diamond on our Wheel, DG-Miliano has the highest brilliance of eight historic and modern cuts: 95, against 93 for the Tolkowsky-based T73. Most of its overall lead is scintillation (98 vs 80), which counts facets; the traced gain in fire is 4 points.\n\nVideo: [The T73 beside DG-Miliano, turning at true size](https://www.youtube.com/watch?v=I59HWHCfrlk)\n\nThe T73 beside DG-Miliano, turning at true size. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nThe T73 beside DG-Miliano, turning at true size.\n\n## 107 years on the same numbers\n\nTolkowsky's proportions became the foundation of the modern round. A century later, the benchmark on our own Wheel, the [T73](https://digitalgemology.com/cuts/t73-round-brilliant), still uses his 40.75° and 34.5°. His numbers became a ceiling as much as a foundation. They were hard to argue with, as long as nobody could trace the light well enough to do better. In our models, even the [hearts and arrows](https://digitalgemology.com/learn/historic-cuts/hearts-and-arrows-diamonds) round runs on his angles.\n\n[Tolkowsky's model](https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919) had three limits: a flat slice, light only from straight above, no more than two reflections. Today a computer does each of those routinely.\n\n## The technology: ray tracing, CAD and the cutting file\n\n**Ray tracing in 3D.** Our Cut Performance Wheel fires 3,200 rays into a full 3D model of the stone, from near-vertical directions. It follows each ray for up to 12 reflections, through every facet. Then it tilts the stone by 20° and does it again with 2,200 more. That is the measurement Tolkowsky couldn't make, and it runs in a browser.\n\n**Design on screen.** Today a designer draws a cut in CAD, scores it, changes it and scores it again, many times before a stone exists. That loop is how we make our house cuts.\n\n**The cutting file.** The finished design becomes a faceting diagram on a standard 96-tooth index wheel. A cutter with an ordinary faceting machine can then reproduce it.\n\n## What DG-Miliano changes\n\n[DG-Miliano](https://digitalgemology.com/cuts/dg-miliano) is one of our house cuts. We drew it for moissanite, but like every cut in the table below we measure it here in diamond. It keeps the modern round's crown plan (8 stars, 8 crown mains, 16 upper girdle facets) and changes three things:\n\n- **A shallower crown**: 32.0° instead of 34.5°.\n- **A multi-angle pavilion**: three tiers of 16 facets instead of one set of mains and halves. The mains sit at 38.3°, below Tolkowsky's 40.75°.\n- **A faceted girdle of 96 facets.**\n\nThat's **177 facets** in all (81 on crown and pavilion, plus 96 on the girdle), against the T73's 73. The stone is 60.3% deep.\n\n![The T73 and DG-Miliano face down, edges drawn: one tier of mains against three tiers.](https://digitalgemology.com/img/learn/hb-l8-t73-vs-dg-miliano-pavilion-mesh.webp?v=4e462aa5)\n\nThe T73 and DG-Miliano face down, edges drawn: one tier of mains against three tiers.\n\n### Try it yourself\n\n1. Open [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel) with `?cut=dg-miliano&stone=diamond`. The comparison cut is the T73. Read all eight rows, not just the top three.\n2. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with `?cut=dg-miliano&stone=diamond`, **Turn** on Slow, lighting **Sunny day**. Then load the T73 and the [old single](https://digitalgemology.com/learn/historic-cuts/old-single-cut-diamond), the oldest cut in the table below.\n3. Go back to the Wheel. Load each of the eight cuts in the table below in diamond and write down brilliance, fire and scintillation.\n\n## What the Wheel shows\n\n**Ahead on all three.** DG-Miliano scores **95** for brilliance, **82** for fire and **98** for scintillation, against the T73's 93, 78 and 80. On the Wheel's Global score it's 93 against 90. On our [diamond page](https://digitalgemology.com/gemstones/diamond) it ranks first of the top-ten brilliants.\n\nVideo: [The Cut Performance Wheel, the T73 giving way to DG-Miliano](https://www.youtube.com/watch?v=nRfAtkyY0C0)\n\nThe Cut Performance Wheel, the T73 giving way to DG-Miliano. · 10 s · No sound\n\n**Read it honestly.** Most of the gap is scintillation: +18 points. The Wheel counts scintillation from the facets, and DG-Miliano has 177 against 73. That's a real design choice, but it's a count, not a traced result. The traced gains are smaller: **+2** in brilliance and **+4** in fire. And not every row goes up. On **Tilt**, how well brightness holds when the stone is tipped 20°, it scores 90 against the T73's 92. These are simulation results for an ideal model: \"a simulation, not a grading report\", as our [method page](https://digitalgemology.com/about/how-we-measure/performance-wheel) says. A few points is a small margin.\n\n**What is new.** Not the facets alone. Tolkowsky's method had no way to test the shallower crown and the lower, three-tier pavilion. Their effect only shows when you follow the light in 3D, from many directions, through many bounces. That is the new step. The gains are small, far smaller than the bruting machine's. But they come from a new way of designing: trace the light first, then choose the angles.\n\n## The whole story in one table\n\n| Cut | Era | Facets | Technology it depended on | Brilliance | Fire | Scintillation |\n| --- | --- | --- | --- | --- | --- | --- |\n| [Old single](https://digitalgemology.com/learn/historic-cuts/old-single-cut-diamond) | 1400s | 18 | Polishing wheel and diamond powder | 72 | 84 | 44 |\n| [Mazarin](https://digitalgemology.com/learn/historic-cuts/mazarin-cut-diamond) | 1650s | 34 | Same; skill | 65 | 63 | 61 |\n| [Peruzzi](https://digitalgemology.com/learn/historic-cuts/peruzzi-cut-diamond) | 1690s | 58 | Same; skill | 75 | 68 | 81 |\n| [Old mine](https://digitalgemology.com/learn/historic-cuts/old-mine-cut-diamond) | 1700s | 58 | Hand refinement; Brazil rough | 59 | 72 | 81 |\n| [Old European](https://digitalgemology.com/learn/historic-cuts/old-european-cut-diamond) | 1870s | 58 | Bruting machine, gauges; South African rough | 90 | 74 | 81 |\n| [T57 (Tolkowsky)](https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919) | 1919 | 57 | Saw, lathe, mathematics | 92 | 79 | 72 |\n| [Hearts and arrows (our T73)](https://digitalgemology.com/learn/historic-cuts/hearts-and-arrows-diamonds) | 1985–1990s | 57 | Reflector viewers; cutting to optical symmetry | 93 | 78 | 80 |\n| DG-Miliano | 2026 | 177 | 3D ray tracing, CAD, cutting files | 95 | 82 | 98 |\n\nScores are our Wheel's, in diamond, for our models. Facet counts in the table are table, crown, pavilion and culet. We count girdle facets only for DG-Miliano, because its girdle is part of the design. Our historic models also carry girdle facets:\n\n- 8 on the old single and Mazarin\n- 16 on the Peruzzi, old mine, old European and T73.\n\nThat's why their scintillation is higher than this column suggests: scintillation counts every facet. Faceted girdles are a recent habit (see [the Peruzzi](https://digitalgemology.com/learn/historic-cuts/peruzzi-cut-diamond)). On plain girdles, the Wheel's own formula would give the old single 33, the Mazarin 53, and the Peruzzi, old mine and old European 72, level with the T57.\n\n## Key points\n\n- Tolkowsky's 1919 proportions were a foundation and, for a century, a ceiling.\n- Today's tools follow light in 3D, from many directions, through up to 12 reflections. A designer can draw and score a cut on screen before anyone cuts it.\n- DG-Miliano: a shallower crown (32.0°), a three-tier pavilion with mains at 38.3°, a 96-facet girdle, 177 facets.\n- In diamond it scores 95 / 82 / 98 against the T73's 93 / 78 / 80, and ranks first of our top-ten brilliants.\n- Most of the lead is scintillation, which is a facet count. The traced gains in brilliance and fire are 2 and 4 points, and tilt is 2 points lower.\n\n**Go further:** the [DG-Miliano cut page](https://digitalgemology.com/cuts/dg-miliano) has the full diagram, and its 3D model and cutting file if you want to cut or render it yourself.\n\n## Try it free\n\n- [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel): Compare brilliance, fire and scintillation of two cuts, or one cut in two stones.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\nFive questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why.\n\n[Take the quiz](https://digitalgemology.com/skool/quiz/the-history-of-the-brilliant/dg-miliano-past-the-1919-ceiling)\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [DG-Miliano Cut](https://digitalgemology.com/cuts/dg-miliano): 3D files and cutting files, €9.99 each\n- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Try another topic · The bow-tie effect: Fixing a bow-tie: the steep belly of DG-Bowtie](https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie)\n\n[Previous lesson](https://digitalgemology.com/learn/historic-cuts/hearts-and-arrows-diamonds) · [Historic diamond cuts: the history of the brilliant: all lessons](https://digitalgemology.com/learn/historic-cuts) · [All topics](https://digitalgemology.com/learn)"},{"id":"BT-L1","course":"The bow-tie files","lesson_number":1,"title":"The bow-tie effect in diamonds: what it is","url":"https://digitalgemology.com/learn/bow-tie/bow-tie-effect-in-diamonds","path":"/learn/bow-tie/bow-tie-effect-in-diamonds","markdown":"https://digitalgemology.com/learn/bow-tie/bow-tie-effect-in-diamonds.md","summary":"What is the bow-tie effect in a diamond? A dark band across the belly of an elongated stone, made by facets that send no light back to your eye.","queries":["bow tie effect diamond","what is a bow tie in a diamond","bowtie oval diamond"],"quiz":null,"tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/dg-bowtie","https://digitalgemology.com/cuts/marquise"],"text":"[The bow-tie effect](https://digitalgemology.com/learn/bow-tie) · 5 min read\n\n# The bow-tie effect in diamonds: what it is\n\nThe bow-tie effect is a dark band across the belly of an elongated diamond, pinched in the middle like a bow tie. It isn't an inclusion or a color: it is a group of facets that, at the angles they were cut, send no light back to your eye.\n\nVideo: [DG-Bowtie face up, turning under Home lighting](https://www.youtube.com/watch?v=EZGJVq14WXA)\n\nDG-Bowtie face up, turning under Home lighting: the band turns with the stone. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nDG-Bowtie face up, turning under Home lighting: the band turns with the stone.\n\n## Two marquises, one dark bar\n\nHere are two marquise diamonds, 1.00 ct each, D, Flawless, face up in the same room.\n\nThey have the same outline, 2.06 times as long as wide. They have the same 87 facets, at the same positions around the stone. The one on the left has a dark bar across its middle. The one on the right doesn't.\n\n![DG-Bowtie and the Marquise at 1.00 ct, face up under Home lighting, at true size.](https://digitalgemology.com/img/learn/bt-l1-dg-bowtie-vs-marquise-home-face-up.webp?v=e462e462)\n\nDG-Bowtie and the Marquise at 1.00 ct, face up under Home lighting, at true size.\n\nThat dark bar is a **bow-tie**. The stone on the left is **[DG-Bowtie](https://digitalgemology.com/cuts/dg-bowtie)**, the first marquise in our library. When we remodeled the [Marquise](https://digitalgemology.com/cuts/marquise), we kept the original under its own name, because it shows a bow-tie so clearly. The stone on the right is the remodel.\n\nAll our [bow-tie pages](https://digitalgemology.com/learn/bow-tie) work on that pair. [Fixing a bow-tie](https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie) shows exactly what we changed, and what it cost. (You may also notice that the Marquise looks bigger at the same weight. [Why bow-ties are still cut](https://digitalgemology.com/learn/bow-tie/why-cutters-leave-a-bow-tie) explains it.)\n\n## The parts of an elongated stone\n\nTo talk about a bow-tie, you need three words. GIA's oval guide uses them, so with them you can read any article on bow-ties:\n\n- **Head or end:** each end of the stone. On a marquise, the ends are **points**.\n- **Shoulder:** where the outline curves away from the end.\n- **Belly:** the wide middle.\n\nA bow-tie is a dark band across the **belly**, from one side to the other. It's pinched in the middle. So it looks like two dark wedges that meet at the center, like a bow tie.\n\nWatch the stone turn in the video at the top of this page. The band goes with it. It isn't a reflection of something in the room. It belongs to the stone.\n\n## What a bow-tie isn't\n\nIt isn't an inclusion, a color, dirt or the setting. Every source we read treats it as an effect of light and cut. Our stone proves it: DG-Bowtie is set to D, Flawless, with nothing inside it at all. The band is still there.\n\nSo where does a dark area in a flawless, colorless diamond come from?\n\n## Why a facet goes dark\n\nA diamond makes no light of its own. It only redirects light that arrives from somewhere else. Each facet you see face up is a small window. Behind it, light bounces through the stone and either comes back to your eye from somewhere bright, or it doesn't.\n\nThe angle of the facet decides which way each window \"looks\". That's geometry. It doesn't change in a drawer, in a safe or on your hand.\n\nSo a bow-tie is a group of facets across the belly that send no light back to your eye, at the angles they have. Those angles were set when the stone was cut.\n\n## Our instrument: the light map\n\nTo see where each facet's light comes from, we use the simulator's **Light map**. It traces the stone face up. It colors every point by the direction its light came from, measured as a height above the girdle:\n\n- **Red, direct:** from 45° to 75° up. The bright light from above.\n- **Green, indirect:** from below 45°. Low, softer light.\n- **Blue, contrast:** from 75° up to straight overhead, within 15° of your line of sight. That's where your own head is.\n- **Black, leakage:** light that never comes back up to you. It leaves through the back of the stone, comes from below the horizon, or is still bouncing after 18 reflections.\n\nThe map uses the stone's geometry alone. No lighting scene and no color enter it. The AGS's ASET maps work on the same idea, and GIA now issues them. They show leakage in gray. Ours shows it in black.\n\n![The T73 round brilliant's light map, face up: a red field of direct light, a blue eight-pointed star of contrast, almost no black.](https://digitalgemology.com/img/learn/bt-l1-t73-light-map.webp?v=d4d61368)\n\nThe T73 round brilliant's light map, face up: a red field of direct light, a blue eight-pointed star of contrast, almost no black.\n\nLearn the colors on a round first. The T73 is orderly: Light Return 69% direct, 5% indirect, 22% contrast and only 4% leakage.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with DG-Bowtie in diamond. Set the lighting to **Home** and the view to **Face up**. Find the band and the belly.\n2. Switch the cut to **Marquise**. Change nothing else.\n3. Switch the cut to the **T73**. Turn on **Light map** and read the **Light Return** bar.\n4. Switch the cut back to **DG-Bowtie**, with the light map still on.\n5. **The challenge:** before you read the bar, guess which color fills DG-Bowtie's band, and what share of the stone it covers. Then check. Last of all, look at the Marquise.\n\n## What the light map shows\n\nDG-Bowtie's band is **black**. Its Light Return reads 15% direct, 21% indirect, 5% contrast and 59% leakage. More than half of what you see face up sends no light back to you. The biggest black area is the belly: the two wedges of the bow-tie. The rest lies scattered toward the points.\n\n![DG-Bowtie's light map, face up: a black bow-tie across the belly, with two small red triangles inside it.](https://digitalgemology.com/img/learn/bt-l1-dg-bowtie-light-map.webp?v=0fc2b573)\n\nDG-Bowtie's light map, face up: a black bow-tie across the belly, with two small red triangles inside it.\n\nThe Marquise reads 47% direct, 22% indirect, 6% contrast and 25% leakage. Its belly is the reddest part of the stone. The outline and the facets are the same: only the angles changed.\n\n![The T73, DG-Bowtie and the Marquise, 1.00 ct each, light maps at true size.](https://digitalgemology.com/img/learn/bt-l1-light-maps-t73-dg-bowtie-marquise.webp?v=84d0cee8)\n\nThe T73, DG-Bowtie and the Marquise, 1.00 ct each, light maps at true size.\n\nThe map tells you that the bar is in the geometry. It doesn't yet tell you why the facets look where they do. And it doesn't tell you why some people never notice the bar in a shop. That leaves an honest question: **is the bar in the stone, or in the room?** We answer it in [Bow-tie in the stone, sometimes on your finger](https://digitalgemology.com/learn/bow-tie/bow-tie-tilt-and-head-shadow).\n\n## Key points\n\n- A bow-tie is a dark band across the belly of an elongated stone, pinched in the middle.\n- The parts are the head or end (on a marquise, the points), the shoulders and the belly.\n- It isn't an inclusion, a color or the setting: it shows in a D, Flawless stone.\n- A diamond only redirects light. A facet is dark when, at the angle it was cut, it sends no light back to you.\n- In the light map, DG-Bowtie's band is black: 59% leakage, against 25% for the Marquise with the same outline and facets.\n\n## Sources\n\n- GIA 4Cs, *Oval Cut Diamond Guide*, 23 September 2025: the parts of an oval (head or end, shoulder, belly).\n- GIA, *AGS Ideal Report* training module, 2024: the ASET map's four colors.\n\n**Go further:** the [DG-Bowtie cut page](https://digitalgemology.com/cuts/dg-bowtie) has its specifications, its light map and its scores in seven gemstones.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\n1. What is a bow-tie?\n  1. An inclusion across the middle of the stone\n  2. A dark band across the belly, made by facets that send no light back\n  3. A reflection of the prongs\n  ### Show the answer\n  **b**: A group of facets across the belly that send no light back to your eye.\n2. In our light map, what does blue mean?\n  1. Light that leaks out of the back\n  2. Light from within 15° of your line of sight, where your head is\n  3. The stone's fire\n  ### Show the answer\n  **b**: Contrast: light from 75° and above, where your own head is.\n3. DG-Bowtie and the Marquise share an outline and 87 facets. What differs between them?\n  1. The material\n  2. The facet angles\n  3. The clarity grade\n  ### Show the answer\n  **b**: Same outline, same facets in the same positions; only the angles changed.\n4. You set DG-Bowtie to D, Flawless in the simulator. What happens to the band?\n  ### Show the answer\n  Nothing. It's already D, Flawless, and the band is still there: it's made by the cut, not the material.\n5. In the simulator, what share of DG-Bowtie's face is leakage, and which color fills its band?\n  ### Show the answer\n  59% leakage; the band is black.\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [DG-Bowtie Cut](https://digitalgemology.com/cuts/dg-bowtie): 3D files and cutting files, €9.99 each\n- [Marquise Cut](https://digitalgemology.com/cuts/marquise): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Which diamond shapes get a bow-tie: oval, pear, marquise and more](https://digitalgemology.com/learn/bow-tie/which-diamond-shapes-have-a-bow-tie)\n- [Try another topic · Historic diamond cuts: the history of the brilliant: Old European cut diamonds: when the outline went round](https://digitalgemology.com/learn/historic-cuts/old-european-cut-diamond)\n\n[The bow-tie effect: all lessons](https://digitalgemology.com/learn/bow-tie) · [All topics](https://digitalgemology.com/learn)"},{"id":"BT-L2","course":"The bow-tie files","lesson_number":2,"title":"Which diamond shapes get a bow-tie: oval, pear, marquise and more","url":"https://digitalgemology.com/learn/bow-tie/which-diamond-shapes-have-a-bow-tie","path":"/learn/bow-tie/which-diamond-shapes-have-a-bow-tie","markdown":"https://digitalgemology.com/learn/bow-tie/which-diamond-shapes-have-a-bow-tie.md","summary":"Which diamond shapes get a bow-tie? Ovals, pears and marquises, never the round. We compare four published lists and show the real criterion.","queries":["oval diamond bow tie","pear diamond bow tie","marquise bow tie"],"quiz":null,"tools":["https://digitalgemology.com/tools/3d_gemstone_simulator","https://digitalgemology.com/tools/cut-performance-wheel"],"cuts":["https://digitalgemology.com/cuts/oval","https://digitalgemology.com/cuts/pear","https://digitalgemology.com/cuts/marquise","https://digitalgemology.com/cuts/dg-bowtie"],"text":"[The bow-tie effect](https://digitalgemology.com/learn/bow-tie) · 6 min read\n\n# Which diamond shapes get a bow-tie: oval, pear, marquise and more\n\nAll four sources we read link the bow-tie to ovals, pears and marquises, and none to the round. The cause is the outline: an elongated stone needs a spread of pavilion angles (7.6° in our Oval, 12.0° in our Marquise, 13.8° in our Pear).\n\n## Four lists\n\n[DG-Bowtie](https://digitalgemology.com/cuts/dg-bowtie), a marquise, has a [dark band across its belly](https://digitalgemology.com/learn/bow-tie/bow-tie-effect-in-diamonds). The next question everyone asks is: which other shapes get one?\n\nFour well-known sources answer it, each from long experience with real stones:\n\n| Shape | GIA's shape guides | Natural Diamond Council | Estate Diamond Jewelry | Ritani |\n| --- | --- | --- | --- | --- |\n| Oval | \"always present\", in some degree | listed | among the most common | \"will exhibit\" it |\n| Pear | \"many\" show one | listed | among the most common | \"can also\" show one |\n| Marquise | \"typically\" some degree | listed | among the most common | \"can also\" show one |\n| Heart | (no guide read) | listed | among the most common | \"sometimes even\" |\n| Radiant | (no guide read) | not listed | \"possible\" in its table | \"sometimes even\" |\n| Cushion | (no guide read) | not listed | prose: no; table: possible; FAQ: can | not prone |\n| Princess | (no guide read) | not listed | table: no; FAQ: cannot | not prone |\n| Round | not listed | not listed | no | not prone |\n\nThey agree on the core: ovals, pears and marquises, and never the round. After that, the lists differ. Estate Diamond Jewelry gives the cushion three different answers in three parts of one guide. That isn't carelessness. \"Cushion\" is a name for an outline, and two cushions can have completely different facet designs inside it.\n\nTwo of the sources also give a reason. Ritani says round, cushion and princess are spared for two reasons: light is evenly distributed in them, and they're \"symmetrically shaped\". Estate Diamond Jewelry says the effect typically occurs in elongated cuts that follow the brilliant faceting pattern. Let's test both reasons.\n\n## Symmetry, or distance?\n\nOur [Oval](https://digitalgemology.com/cuts/oval) and our [Marquise](https://digitalgemology.com/cuts/marquise) are perfectly symmetric: each half mirrors the other, lengthwise and across (the cut pages say \"2-fold mirror-image symmetry\"). So symmetry alone can't separate a round from an oval.\n\nWhat separates them is **distance**. Measure from the center of the stone out to the girdle:\n\n- In a **round**, it's the same in every direction.\n- In an **elongated** stone, it's short across the belly and long toward the ends. In our Marquise, the distance to a point is 2.06 times the distance to the side.\n\nNow look at the pavilion. All its facets slope down from the girdle to the bottom of the stone. The bottom sits at one depth: a point in a round, a short line (the keel) in a marquise. A facet that starts close to the center, across the belly, must slope **steeply** to reach that depth. A facet that starts far out, toward a point, slopes **gently**.\n\nSo a round can use one main pavilion angle all the way round. The T73 uses 40.75°, the angle Marcel Tolkowsky worked out for diamond in 1919. An elongated stone can't. It needs a **spread** of pavilion angles, and only some of its facets can sit near that ideal. Our cutting files show the spread:\n\n| Cut | Length to width | Pavilion angles | Spread |\n| --- | --- | --- | --- |\n| T73 | 1.00 | 40.75° | one main angle |\n| Oval | 1.33 | 35.7° to 43.3° | 7.6° |\n| Marquise | 2.06 | 30.5° to 42.5° | 12.0° |\n| Pear | 1.50 | 33.2° to 47.0° | 13.8° |\n\nThe pear isn't the longest, but it's the most lopsided: a round end on one side and a point on the other. Its angles vary the most.\n\nThat's the criterion behind every list: **how much the distance from the center changes around the girdle, and how sharp the ends are**. GIA's pear guide puts it in one line: a bow-tie gets darker as the difference between length and width increases and \"pavilion angle variations become more extreme\". Estate Diamond Jewelry's word \"elongated\" was the right one. A cushion or a princess can sit anywhere on that scale: its design decides where. That is why the lists can't agree on them.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator). Turn on **Light map** and load the **T73**. Read its leakage on the **Light Return** bar.\n2. **The ranking game.** Before you load them, rank the **Oval**, the **[Pear](https://digitalgemology.com/cuts/pear)** and the **Marquise** by how much they leak, from least to most. Write your guess down.\n3. Load each one and read its leakage. Where does the black sit: a band across the belly, the ends, or scattered?\n4. Open [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel) with the **Marquise** in diamond. Compare it with the **Oval**.\n\n## What the light maps show\n\n![The T73, Oval, Pear and Marquise, 1.00 ct each, light maps at true size.](https://digitalgemology.com/img/learn/bt-l2-light-maps-t73-oval-pear-marquise.webp?v=a0cf73e6)\n\nThe T73, Oval, Pear and Marquise, 1.00 ct each, light maps at true size.\n\n| 1.00 ct diamond | Direct | Indirect | Contrast | Leakage |\n| --- | --- | --- | --- | --- |\n| T73 | 69% | 5% | 22% | 4% |\n| Marquise | 47% | 22% | 6% | 25% |\n| Pear | 35% | 26% | 8% | 31% |\n| Oval | 33% | 27% | 3% | 38% |\n\nMost people guess the Marquise leaks most: it's the longest and the pointiest. It leaks least of the three. Its belly is solid red. The Pear's black is scattered toward its point. The Oval's black sits in two patches at its ends, not across its belly.\n\n![The Cut Performance Wheel, Marquise against Oval in diamond.](https://digitalgemology.com/img/learn/bt-l2-wheel-marquise-vs-oval.webp?v=f321f78a)\n\nThe Cut Performance Wheel, Marquise against Oval in diamond.\n\nThe Wheel says the same thing: brilliance 64 for the Marquise against 47 for the Oval. Fire (89 and 92) and scintillation (86 and 87) are close.\n\nSo the marquise is the **hardest** outline to cut well. It is the most stretched of the common shapes and pointed at both ends, with a 12° spread of pavilion angles to manage. Hardest isn't condemned. The angles decide, and DG-Bowtie has the very same outline as our best-scoring elongated stone. [Fixing a bow-tie](https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie) shows where its angles went instead.\n\nOne side note on facet counts. GIA's oval guide says most ovals have 57 or 58 facets. Our Oval's cutting design has 93. More tiers give a cutter more angles to tune around the outline. But they don't fix a bow-tie by themselves: DG-Bowtie and the Marquise both have 87.\n\n## Key points\n\n- The published lists agree on ovals, pears and marquises, and never the round. They differ on cushions, princesses, hearts and radiants, because each of those names covers many facet designs.\n- Symmetry doesn't separate a round from an oval: both are symmetric. Distance from the center does.\n- A round can use one main pavilion angle. An elongated stone needs a spread: 7.6° in our Oval, 12.0° in the Marquise and 13.8° in the Pear.\n- The marquise is the hardest case, but our Marquise leaks less (25%) than our Pear (31%) and Oval (38%).\n- The facet count doesn't decide it: DG-Bowtie and the Marquise both have 87 facets.\n\n## Sources\n\n- GIA 4Cs, *Oval Cut Diamond Guide*, 23 September 2025: bow-tie always present in some degree; 57 or 58 facets.\n- GIA 4Cs, marquise diamond guide, 29 November 2016, and pear diamond guide, 13 March 2018: bow-ties typical in marquises and shown by many pears.\n- Grant Mobley, \"The Bow Tie Effect in Diamonds: What It Is and Why It Shouldn't Scare You\", Only Natural Diamonds (Natural Diamond Council), 31 March 2026: ovals, pears, marquises and hearts.\n- Benjamin Khordipour, diamond bow-tie effect guide, Estate Diamond Jewelry, updated 15 April 2026: shapes table, cushion and princess answers, \"elongated cuts\".\n- Kristin P, \"What is a bow tie in an oval diamond\", Ritani, 13 October 2025: shapes, \"symmetrically shaped\".\n\n**Go further:** the [Marquise cut page](https://digitalgemology.com/cuts/marquise) has its specifications and its scores in seven gemstones.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n- [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel): Compare brilliance, fire and scintillation of two cuts, or one cut in two stones.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\n1. Which shapes do all four sources link to bow-ties?\n  1. Round, cushion and princess\n  2. Oval, pear and marquise\n  3. Heart and radiant only\n  ### Show the answer\n  **b**: They differ on the others.\n2. Why can a round brilliant use one main pavilion angle all the way round?\n  1. It has more facets\n  2. Its girdle is the same distance from the center in every direction\n  3. It's more symmetric than an oval\n  ### Show the answer\n  **b**: The same distance everywhere means the same slope down to the culet everywhere.\n3. In an elongated stone, which pavilion facets slope most steeply?\n  1. The ones across the belly\n  2. The ones at the points\n  3. They all slope the same\n  ### Show the answer\n  **a**: They start closest to the center, so they must slope most steeply to reach the same depth.\n4. A friend says the marquise is the worst shape for bow-ties, so every marquise has one. What does our Marquise show?\n  ### Show the answer\n  Hardest isn't condemned: our Marquise has a solid red belly and leaks only 25%, less than our Pear or Oval.\n5. In the simulator, rank the T73, Oval, Pear and Marquise by leakage. Which surprised you?\n  ### Show the answer\n  T73 4%, Marquise 25%, Pear 31%, Oval 38%. Most people expect the Marquise to be last.\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [Oval Cut](https://digitalgemology.com/cuts/oval): 3D files and cutting files, €9.99 each\n- [Pear Cut](https://digitalgemology.com/cuts/pear): 3D files and cutting files, €9.99 each\n- [Marquise Cut](https://digitalgemology.com/cuts/marquise): 3D files and cutting files, €9.99 each\n- [DG-Bowtie Cut](https://digitalgemology.com/cuts/dg-bowtie): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Bow-tie in the stone, sometimes on your finger: tilt and head shadow](https://digitalgemology.com/learn/bow-tie/bow-tie-tilt-and-head-shadow)\n- [Try another topic · How to read a diamond grading report: The grades on a diamond report: color, clarity and cut](https://digitalgemology.com/learn/grading-reports/diamond-report-grades)\n\n[Previous lesson](https://digitalgemology.com/learn/bow-tie/bow-tie-effect-in-diamonds) · [The bow-tie effect: all lessons](https://digitalgemology.com/learn/bow-tie) · [All topics](https://digitalgemology.com/learn)"},{"id":"BT-L3","course":"The bow-tie files","lesson_number":3,"title":"Bow-tie in the stone, sometimes on your finger: tilt and head shadow","url":"https://digitalgemology.com/learn/bow-tie/bow-tie-tilt-and-head-shadow","path":"/learn/bow-tie/bow-tie-tilt-and-head-shadow","markdown":"https://digitalgemology.com/learn/bow-tie/bow-tie-tilt-and-head-shadow.md","summary":"Why a diamond's bow-tie can show on your hand but not in the shop: the room, the tilt and your head change what you see. The cut decides if it's there.","queries":["bow tie oval diamond on hand","bow tie only in photos","head shadow diamond"],"quiz":null,"tools":["https://digitalgemology.com/tools/brightness-tilt-analysis","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/dg-bowtie","https://digitalgemology.com/cuts/marquise"],"text":"[The bow-tie effect](https://digitalgemology.com/learn/bow-tie) · 6 min read\n\n# Bow-tie in the stone, sometimes on your finger: tilt and head shadow\n\nA bow-tie is always in the stone, but only sometimes visible on your hand. The room decides whether you see it: DG-Bowtie's band shows white in a photo studio and dark at home, while its light map, which reads only the geometry, never changes.\n\nVideo: [DG-Bowtie and the Marquise tilting −30° to +30°, 30° head shadow](https://www.youtube.com/watch?v=TbluZpEHEys)\n\nBrightness & Tilt, DG-Bowtie against the Marquise tilting from −30° to +30° under the largest head shadow, 30°. · 10 s · No sound\n\n## Transcript\n\nThis 10-second clip has no sound. What you see:\n\nBrightness & Tilt, DG-Bowtie against the Marquise tilting from −30° to +30° under the largest head shadow, 30°.\n\n## Same stone, four rooms\n\n[What a bow-tie is](https://digitalgemology.com/learn/bow-tie/bow-tie-effect-in-diamonds) ends on a question: is the dark bar in the stone, or in the room?\n\nHere's [DG-Bowtie](https://digitalgemology.com/cuts/dg-bowtie), a 1.00 ct marquise with a bow-tie, face up in four of the simulator's rooms.\n\n![DG-Bowtie face up under Photo studio, Shopping center, Home and Cloudy day lighting.](https://digitalgemology.com/img/learn/bt-l3-dg-bowtie-four-rooms.webp?v=657237ac)\n\nDG-Bowtie face up under Photo studio, Shopping center, Home and Cloudy day lighting.\n\n- **Photo studio:** the bow-tie is **bright white**, a flat, glassy patch in the middle of a sparkling stone.\n- **Shopping center:** pale gray glass.\n- **Home:** a dark bar.\n- **Cloudy day:** pale again.\n\nNobody swapped the stone. In three of these rooms you'd hardly call the middle \"dark\" at all. This is the moment a buyer describes as \"it looked perfect in the shop, and then I got it home\".\n\n## The light map doesn't move\n\nNow turn on the light map and go through the same four rooms.\n\n![DG-Bowtie's light map under the same four lightings: four identical maps.](https://digitalgemology.com/img/learn/bt-l3-dg-bowtie-light-map-four-rooms.webp?v=8017ca22)\n\nDG-Bowtie's light map under the same four lightings: four identical maps.\n\nFour identical maps. The light map traces the geometry alone. No lighting scene enters it. The black band is in exactly the same place in every room, because the facets that make it are in exactly the same place.\n\nSo both halves of the answer are true at once:\n\n> **The bow-tie is always in the stone. It is only sometimes on your finger.**\n\n## Why the band changes color\n\nFollow the light backward, from your eye into the stone. Across DG-Bowtie's belly, the path goes in through the table and reflects off one belly facet. Then it leaves through the opposite facet, out of the **back** of the stone. (That's what black means on the map: [Fixing a bow-tie](https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie) shows exactly why it leaves.)\n\nSo those facets don't show you a lamp above. They show you **whatever is underneath the stone**.\n\n- In the **Photo studio**, softboxes surround the camera and a lamp lights the space below the stone. The band looks through the stone at something bright, so it shows white.\n- At **Home**, there's a table lamp and a ceiling light, and very little light below the stone. The band shows dark.\n\nOn a hand, what's under the stone is the setting and your finger.\n\nVideo: [DG-Bowtie turning face up in the Photo studio](https://www.youtube.com/watch?v=9HkEQJ869OA)\n\nDG-Bowtie turning face up in the Photo studio: the bow-tie shows white. · 10 s · No sound\n\n## Where the light is, not how bright it is\n\nThe usual explanation for \"it looked fine in the shop\" is that the shop is brighter. Brightness alone can't do it. Double every lamp, and the bright facets double. The little light that reaches the dark ones doubles too. Their ratio stays the same, and your eye reads that ratio as contrast. So the band stays.\n\nWhat changes the picture is **where** the light is: whether there's something bright in the directions those facets look. A shop puts many small lights around the stone, often over a pale counter. A living room has one window and a lot of dark wall, and your own head over the stone.\n\nThe **Brightness & Tilt Analysis** shows this in numbers. We compare DG-Bowtie with our [Marquise](https://digitalgemology.com/cuts/marquise), which has the same outline and facets but different angles. The tool's figures are shares of the available light, so a brighter dome changes nothing. What changes the figures is the shape of the light:\n\n- **ISO:** light from every direction above the stone.\n- **COS:** bright overhead, fading toward the horizon.\n- **SC2:** a ring of light at about 45°, dark overhead.\n- **Head shadow:** how much of the sky overhead your head blocks, from 0° to 30°.\n\n| Diamond, face up | DG-Bowtie, head shadow 0° | DG-Bowtie, 30° | Marquise, 0° | Marquise, 30° |\n| --- | --- | --- | --- | --- |\n| ISO | 35.3% | 23.2% | 70.6% | 47.2% |\n| COS | 23.6% | 11.8% | 47.8% | 25.6% |\n| SC2 | 21.0% | 18.7% | 45.4% | 35.7% |\n| Leakage | 59.5% | 59.5% | 22.1% | 22.1% |\n\n![Brightness & Tilt, DG-Bowtie against the Marquise, head shadow 0° and 30°.](https://digitalgemology.com/img/learn/bt-l3-bt-head-shadow-0.webp?v=640971e1) ![Brightness & Tilt, DG-Bowtie against the Marquise, head shadow 0° and 30°.](https://digitalgemology.com/img/learn/bt-l3-bt-head-shadow-30.webp?v=904c05f9)\n\nBrightness & Tilt, DG-Bowtie against the Marquise, head shadow 0° and 30°.\n\nA bigger head darkens both stones in every model. Leakage doesn't move at all. Brightness & Tilt counts leakage its own way. So its figures differ a little from the simulator's Light Return: 59.5% against 59% for DG-Bowtie, and 22.1% against 25% for the Marquise. Those paths look out of the back of the stone, where no dome model puts any light. So no arrangement of light above can brighten them.\n\nNow tip the stones, as a hand does. The video at the top of this page shows the tilt under the largest head shadow, 30°. This one shows it with no head shadow:\n\nVideo: [DG-Bowtie and the Marquise tilting −30° to +30°, no head shadow](https://www.youtube.com/watch?v=cJu0LswI3WQ)\n\nBrightness & Tilt, DG-Bowtie against the Marquise tilting from −30° to +30°, no head shadow. · 10 s · No sound\n\nCompare the two videos. At every tilt, both stones are darker under the head. The leakage figure under each Light Return window is the same in both videos, frame for frame. The head bites hardest **face up**. Under ISO, the Marquise loses 23.5 points face up (70.6% to 47.1%), but 16.8 at a 30° tilt (57.8% to 41.0%). Face up is the view where you look straight down over the stone. It is also the view people judge a bow-tie in.\n\n## Close the door\n\nIt is easy to misread all this as \"so it's only the lighting, my stone is fine\". Look at the two marquises again, in the same Home light and the same view. DG-Bowtie shows the band. The Marquise doesn't.\n\n![DG-Bowtie and the Marquise face up under the same Home lighting.](https://digitalgemology.com/img/learn/bt-l1-dg-bowtie-vs-marquise-home-face-up.webp?v=e462e462)\n\nDG-Bowtie and the Marquise face up under the same Home lighting.\n\nThe room is the same, so the difference is the cut. The room decides **whether you see** the band. The cut decides **whether it's there**.\n\nShop lighting is made to show stones at their best, and it does that honestly. But it isn't a test. And it's usually the only light you see a stone in before you pay.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with DG-Bowtie, view **Face up**. Go through **Photo studio**, **Shopping center**, **Home** and **Cloudy day**.\n2. Turn on **Light map** and go through the same four. Does anything move?\n3. **The hide-and-seek challenge:** of all ten lightings, find the one where DG-Bowtie's band hides best and the one where it shows darkest.\n4. Open [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis) with DG-Bowtie and compare it with the **Marquise**. Move **Head shadow** from 0° to 30°. Watch ISO, then watch Leakage. Then set the head shadow to 0° and drag **Tilt** from −30° to +30°. Do it again at 30°.\n\n## What the simulator and Brightness & Tilt show\n\nThe band changes from white to dark with the room. The light map doesn't change at all. The band's facets look out of the back of the stone, so they show whatever is beneath it. In Brightness & Tilt, the head shadow cuts DG-Bowtie's ISO from 35.3% to 23.2% and the Marquise's from 70.6% to 47.2%. Leakage stays at 59.5% and 22.1%. When you tilt the stones, the head still darkens both at every angle, most of all face up. Leakage still doesn't change with the head. Under the same Home light the Marquise has no band. So the room can show or hide a bow-tie, but it can't make one.\n\n## Key points\n\n- The bow-tie is always in the stone. It is only sometimes on your finger.\n- The light map reads geometry only, so it's identical in every room.\n- DG-Bowtie's band looks out of the back of the stone. It shows white in the Photo studio, pale in the Shopping center and dark at Home.\n- What hides or shows it is where the light is, not how bright it is. A uniformly brighter room changes nothing.\n- Under the same light, the Marquise shows no band. The room decides whether you see it; the cut decides whether it's there.\n\n**Go further:** [How we measure: the simulator](https://digitalgemology.com/about/how-we-measure/simulator) describes the ten rooms and the light map.\n\n## Try it free\n\n- [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis): Face-up brightness under four standard lights, and how it holds as the stone tilts.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\n1. In the simulator, DG-Bowtie's light map under Home and under Photo studio is:\n  1. Darker at Home\n  2. Identical\n  3. Brighter in the studio\n  ### Show the answer\n  **b**: The map reads geometry only.\n2. Why does DG-Bowtie's band show white in the Photo studio?\n  1. The studio is brighter overall\n  2. Its facets look out of the back of the stone, and the studio lights what's underneath\n  3. The studio removes the head shadow\n  ### Show the answer\n  **b**: They show whatever is beneath the stone, and the studio lights it.\n3. A friend says: \"My oval only shows a bow-tie in dim light, so it's the lighting, not the stone.\" What would you test?\n  1. Nothing, they're right\n  2. The same light on a different oval: if one bands and the other doesn't, the cut decides\n  3. A brighter bulb\n  ### Show the answer\n  **b**: The room decides whether you see it; the cut decides whether it's there.\n4. In Brightness & Tilt, what happens to leakage when you raise the head shadow from 0° to 30°?\n  ### Show the answer\n  Nothing: leakage paths look below the horizon, where no dome puts light (59.5% and 22.1% at every setting).\n5. Which of the ten lightings hides DG-Bowtie's band best, and which shows it darkest?\n  ### Show the answer\n  Open answer: in our test, the Photo studio turns it white and Home shows it dark.\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [DG-Bowtie Cut](https://digitalgemology.com/cuts/dg-bowtie): 3D files and cutting files, €9.99 each\n- [Marquise Cut](https://digitalgemology.com/cuts/marquise): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: What causes a bow-tie? Four explanations, tested](https://digitalgemology.com/learn/bow-tie/what-causes-a-bow-tie)\n- [Try another topic · Historic diamond cuts: the history of the brilliant: Tolkowsky's 1919 ideal cut: the brilliant that was calculated](https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919)\n\n[Previous lesson](https://digitalgemology.com/learn/bow-tie/which-diamond-shapes-have-a-bow-tie) · [The bow-tie effect: all lessons](https://digitalgemology.com/learn/bow-tie) · [All topics](https://digitalgemology.com/learn)"},{"id":"BT-L4","course":"The bow-tie files","lesson_number":4,"title":"What causes a bow-tie? Four explanations, tested","url":"https://digitalgemology.com/learn/bow-tie/what-causes-a-bow-tie","path":"/learn/bow-tie/what-causes-a-bow-tie","markdown":"https://digitalgemology.com/learn/bow-tie/what-causes-a-bow-tie.md","summary":"What causes a bow-tie in diamonds? We test four published explanations (your head, leakage, a shadow, the cut) on one marquise in our tools.","queries":["what causes bow tie in diamonds","bow tie effect cause","why do ovals have a bow tie"],"quiz":null,"tools":["https://digitalgemology.com/tools/brightness-tilt-analysis","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/dg-bowtie","https://digitalgemology.com/cuts/marquise","https://digitalgemology.com/cuts/oval"],"text":"[The bow-tie effect](https://digitalgemology.com/learn/bow-tie) · 6 min read\n\n# What causes a bow-tie? Four explanations, tested\n\nA bow-tie is made by facets that look at something dark: out through the back of the stone (leakage), or back at your head. In our DG-Bowtie the band is leakage, 59% of the face; your head adds only 5% contrast, near the points.\n\n## Four sources, four explanations\n\nThe band of a bow-tie [is in the stone](https://digitalgemology.com/learn/bow-tie/bow-tie-tilt-and-head-shadow), and the room decides whether you see it. But what is the band, physically? Four respected sources explain it. Here they are, in their own words:\n\n- **GIA**, in its oval guide, says that blocked light causes the bow-tie, \"specifically by your own head and shoulders\". It also says some degree is present \"due to the nature of the shape and faceting pattern\". Its marquise guide describes the bow-tie as \"a dark contrast where your head and shoulders are reflected\".\n- **The Natural Diamond Council**, in an article by Grant Mobley, says it appears because \"some light escapes through the lower pavilion facets\".\n- **Estate Diamond Jewelry**, in Benjamin Khordipour's guide, puts an Expert Note near the top. It says the effect \"isn't a result of light leakage\" but a \"shadow inside a diamond\". It gives the cause as \"simply an improper light reflection due to the cut\". Further down, its section on the optics explains dark areas by light that escapes \"through the pavilion or girdle\".\n- **Ritani**, in Kristin P's guide, says \"Light blockage is what causes the bow-tie effect\", for example when your head blocks the light. It calls the effect \"basically a shadow within the diamond\".\n\nSo there are three ideas: **your head**, **leakage**, and a **shadow**. Each source states its idea. We'll demonstrate what our stone does.\n\n## The bench: DG-Bowtie's light map\n\nOur simulator's [light map](https://digitalgemology.com/learn/bow-tie/bow-tie-effect-in-diamonds) has a color for two of these ideas:\n\n- **Black, leakage:** light that leaves through the back of the stone.\n- **Blue, contrast:** light from within 15° of your line of sight, the zone your own head blocks.\n\nSo we can ask the map directly about [DG-Bowtie](https://digitalgemology.com/cuts/dg-bowtie), a marquise with a strong bow-tie: is its band black, or blue?\n\n![DG-Bowtie face up at Home beside its light map: the dark band face up is the black band in the map.](https://digitalgemology.com/img/learn/bt-l4-dg-bowtie-face-up-home-vs-light-map.webp?v=7320fb1b)\n\nDG-Bowtie face up at Home beside its light map: the dark band face up is the black band in the map.\n\nIt's black. DG-Bowtie's face is 59% leakage and only 5% contrast. That blue sits in small patches near the points, not across the belly. In this stone, the band is light leaving through the back.\n\n## Is your head real?\n\nYes, and our tools show it. Look at the T73 face up at Home. There's a dark star in the middle of the stone. Now turn on its light map: a blue star in the same place.\n\n![The T73 face up at Home beside its light map: the dark star is the blue contrast star.](https://digitalgemology.com/img/learn/bt-l4-t73-face-up-home-vs-light-map.webp?v=67cc4788)\n\nThe T73 face up at Home beside its light map: the dark star is the blue contrast star.\n\nThat's your head (in the simulator, a head shadow sits right on your line of sight), reflected in the stone's pavilion. In a well-cut round, the facets spread it into a crisp, even pattern. It reads as contrast, and contrast gives a round its sharpness.\n\nThe **Brightness & Tilt** tilt videos on [our tilt and head-shadow page](https://digitalgemology.com/learn/bow-tie/bow-tie-tilt-and-head-shadow) tell the same story. They set DG-Bowtie beside our [Marquise](https://digitalgemology.com/cuts/marquise), which has the same outline and facets but different angles. Under the largest head shadow, both marquises are darker at every tilt. The head costs most face up. Watch the Marquise in the head-shadow video there. Dark patches, your head, wander across it as it tips, and they're in different places at every angle. But DG-Bowtie's leakage figure is the same with or without the head.\n\nSo the head is real. It just isn't what draws the band in DG-Bowtie.\n\n## And the shadow?\n\n\"Shadow\" is a fair word for what the band looks like. But a shadow needs something to block the light. In DG-Bowtie's belly, nothing is in the way. The light path is simply aimed out of the back of the stone. Estate Diamond Jewelry's own optics section describes exactly that, and our map agrees with it. The same Expert Note also gives the cause as \"improper light reflection due to the cut\". That part holds completely.\n\n## The bench, scored\n\n| Claim | Source | On the bench (DG-Bowtie) |\n| --- | --- | --- |\n| Light escapes through the lower pavilion facets | Natural Diamond Council; Estate Diamond Jewelry's optics section | **Held.** The band is black: 59% of the face is leakage. |\n| Your head and shoulders block the light | GIA; Ritani | **Real, but not this band.** Contrast is 5%, near the points. The head darkens every stone. |\n| The shape and faceting pattern play a part | GIA | **Held.** The angles decide where every facet looks. (GIA's \"always present\" gets [its own test](https://digitalgemology.com/learn/bow-tie/is-a-bow-tie-always-present).) |\n| Not leakage, but a shadow inside the stone | Estate Diamond Jewelry's Expert Note | **Didn't hold here.** Nothing blocks the light; the path is aimed out of the back. |\n| Improper light reflection due to the cut | Estate Diamond Jewelry's Expert Note | **Held.** The cut's angles send the light out of the back. |\n| Not an inclusion or a flaw in the material | All four | **Held.** DG-Bowtie is D, Flawless. |\n\nLook again at GIA's sentence. It names both the head and \"the shape and faceting pattern\". Our bench says both belong in the story, in a specific way: **the faceting pattern decides which facets look at your head, and which look out of the back.**\n\nSo here's one explanation that covers all of it:\n\n> A dark facet is a facet that looks at something dark: either out through the back of the stone (leakage), or back at you (your head). The angles decide which.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with DG-Bowtie, view **Face up**, lighting **Home**. Then turn on **Light map**. Find the black and find the blue.\n2. Load the **T73**, face up at Home. Find the dark star. Turn on the light map. What color is it?\n3. Open [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis) with DG-Bowtie against the **Marquise**. Move **Head shadow** from 0° to 30°. Which figures move, and which one doesn't? Then drag **Tilt** and watch where the head's dark patches go.\n4. **Score the bench yourself:** for each of the four sources, write \"held\", \"real but not this band\" or \"didn't hold here\", with one screenshot as evidence.\n\n## What the light map and Brightness & Tilt show\n\nDG-Bowtie's band is black on the map, not blue: leakage, 59% of the face. The blue is 5%, near the points. The T73's dark star face up is the blue star on its map: your head is real. The head shadow lowers every brightness figure, but leakage stays at 59.5% for DG-Bowtie and 22.1% for the Marquise. The leakage explanation held for this stone. The head is real, but it doesn't draw this band. And \"shadow\" describes the look, not the cause.\n\n## Key points\n\n- The four sources give three causes: your head (GIA, Ritani), leakage (NDC, and EDJ's optics section) and a shadow (EDJ's Expert Note, Ritani).\n- On our map, DG-Bowtie's band is black: leakage. In this stone, the leakage explanation held.\n- Your head is real. It's the T73's blue star, and the head shadow darkens every stone. But it isn't what draws DG-Bowtie's band.\n- A dark facet looks at something dark: out of the back of the stone, or back at you. The angles decide which. So GIA's \"shape and faceting pattern\" is right where it matters.\n- All four sources agree it isn't the material, and that held.\n\n## Sources\n\n- GIA 4Cs, *Oval Cut Diamond Guide*, 23 September 2025: head and shoulders; shape and faceting pattern.\n- Grant Mobley, \"The Bow Tie Effect in Diamonds: What It Is and Why It Shouldn't Scare You\", Only Natural Diamonds (Natural Diamond Council), 31 March 2026: light escaping through the lower pavilion facets.\n- Benjamin Khordipour, diamond bow-tie effect guide, Estate Diamond Jewelry, updated 15 April 2026: Expert Note (not leakage, a shadow); optics section (escape through the pavilion or girdle).\n- Kristin P, \"What is a bow tie in an oval diamond\", Ritani, 13 October 2025: light blockage, your head, \"basically a shadow\".\n\n**Go further:** [How we measure: Brightness & Tilt](https://digitalgemology.com/about/how-we-measure/brightness-tilt) explains the head shadow and the three light models.\n\n## Try it free\n\n- [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis): Face-up brightness under four standard lights, and how it holds as the stone tilts.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\n1. Which source explains the bow-tie as light escaping through the lower pavilion facets?\n  1. GIA\n  2. The Natural Diamond Council\n  3. Ritani\n  ### Show the answer\n  **b**: Grant Mobley's article for the NDC.\n2. In our light map, what color would a band made by your own head be?\n  1. Black\n  2. Blue\n  3. Green\n  ### Show the answer\n  **b**: Contrast: light from within 15° of your line of sight.\n3. DG-Bowtie's band is black. What does that tell you?\n  1. The light that should reach your eye leaves through the back of the stone\n  2. Your head is blocking it\n  3. The stone has an inclusion\n  ### Show the answer\n  **a**: Black is leakage; the band's facets look out of the back.\n4. You raise the head shadow from 0° to 30° in Brightness & Tilt. Which figure doesn't change, and why?\n  ### Show the answer\n  Leakage: those paths look out of the back of the stone, where no light model puts any light.\n5. Score one claim on the bench in your own words, with the evidence from the tools.\n  ### Show the answer\n  Open answer, e.g. \"Leakage held: DG-Bowtie's band is black and 59% of its face leaks.\"\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [DG-Bowtie Cut](https://digitalgemology.com/cuts/dg-bowtie): 3D files and cutting files, €9.99 each\n- [Marquise Cut](https://digitalgemology.com/cuts/marquise): 3D files and cutting files, €9.99 each\n- [Oval Cut](https://digitalgemology.com/cuts/oval): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Is a bow-tie always there? How much is normal](https://digitalgemology.com/learn/bow-tie/is-a-bow-tie-always-present)\n- [Try another topic · How to read a diamond grading report: The grades on a diamond report: color, clarity and cut](https://digitalgemology.com/learn/grading-reports/diamond-report-grades)\n\n[Previous lesson](https://digitalgemology.com/learn/bow-tie/bow-tie-tilt-and-head-shadow) · [The bow-tie effect: all lessons](https://digitalgemology.com/learn/bow-tie) · [All topics](https://digitalgemology.com/learn)"},{"id":"BT-L5","course":"The bow-tie files","lesson_number":5,"title":"Is a bow-tie always there? How much is normal","url":"https://digitalgemology.com/learn/bow-tie/is-a-bow-tie-always-present","path":"/learn/bow-tie/is-a-bow-tie-always-present","markdown":"https://digitalgemology.com/learn/bow-tie/is-a-bow-tie-always-present.md","summary":"Is some bow-tie always present, and how much is normal? We stress-test our Marquise and Oval in every room, head shadow and tilt.","queries":["how much bow tie is acceptable","oval without bow tie","bow tie free oval"],"quiz":null,"tools":["https://digitalgemology.com/tools/brightness-tilt-analysis","https://digitalgemology.com/tools/cut-performance-wheel","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/marquise","https://digitalgemology.com/cuts/oval","https://digitalgemology.com/cuts/dg-bowtie"],"text":"[The bow-tie effect](https://digitalgemology.com/learn/bow-tie) · 6 min read\n\n# Is a bow-tie always there? How much is normal\n\nA band of leakage across the belly isn't always present: our Marquise has the same outline as the banded DG-Bowtie, no band, and more brilliance (64 against 27). What every stone shows under a large head shadow is a moving contrast pattern, not a band.\n\n## The biggest claim\n\n[DG-Bowtie](https://digitalgemology.com/cuts/dg-bowtie) is a marquise with a dark band across its belly, and [we tested what that band is made of](https://digitalgemology.com/learn/bow-tie/what-causes-a-bow-tie). Now the claim that matters most to anyone buying a long stone: can a bow-tie be avoided at all?\n\nOur sources answer with different strengths:\n\n- **GIA's oval guide:** a well-cut oval will \"minimize the bow tie\", but because of the shape and faceting pattern, \"some degree of bow tie is always present\".\n- **GIA's marquise guide:** marquises \"typically will have some degree of a bow-tie\", and stones without one \"usually lack brightness\".\n- **The Natural Diamond Council:** some degree \"is almost inevitable in elongated cuts\".\n- **Estate Diamond Jewelry:** every brilliant-cut diamond \"aside from perfectly round diamonds\" has \"some tiny degree of bow tie\".\n\nTwo of them, GIA's oval guide and Estate Diamond Jewelry, say it's always there. GIA's marquise guide calls it typical, and the NDC calls it almost inevitable. These are careful statements, and they come from looking at a great many real stones. But \"always\" is a special word. To test a claim about every stone, you need to find **one** stone it doesn't fit.\n\nOne more thing to settle first: what kind of bow-tie? GIA's marquise guide describes the bow-tie as \"a dark contrast where your head and shoulders are reflected\". DG-Bowtie's band is a different thing: leakage, light leaving through the back. We'll test both.\n\nFirst, two things GIA says that are simply true. GIA gives an overall cut grade only to round brilliants. So a marquise or oval report won't grade its cut. And GIA notes that bow-tie visibility can vary between stones with the same length-to-width ratio. That is a quiet hint that the cut decides, not the shape.\n\n## The counterexample: our Marquise\n\nIt has the same outline as DG-Bowtie, the same 87 facets and different angles.\n\n![The Marquise and the Oval, 1.00 ct, light maps: both bellies red.](https://digitalgemology.com/img/learn/bt-l5-marquise-oval-light-maps.webp?v=a7aee645)\n\nThe Marquise and the Oval, 1.00 ct, light maps: both bellies red.\n\nIts light map: 47% direct, 22% indirect, 6% contrast, 25% leakage. The belly, where the band is supposed to be, is the **reddest** part of the stone. There's black scattered through it, as in every stone, but no band runs across it.\n\nAnd GIA's marquise guide expects a marquise without a bow-tie to lack brightness. Ours is the bright one: brilliance 64 on the Cut Performance Wheel, against DG-Bowtie's 27.\n\n## And an oval, for GIA's oval claim\n\nGIA's \"always present\" is about ovals, so let's test an oval too. Our [Oval](https://digitalgemology.com/cuts/oval)'s belly is red and green, with no band across it. It isn't perfect. It leaks 38%, more than the [Marquise](https://digitalgemology.com/cuts/marquise), and its black collects in **two patches at its ends**. At Home those ends look dark.\n\n![The Oval's light map beside the stone at Home and in the Photo studio: a clean belly, dark ends.](https://digitalgemology.com/img/learn/bt-l5-oval-light-map-home-studio.webp?v=59cbae9e)\n\nThe Oval's light map beside the stone at Home and in the Photo studio: a clean belly, dark ends.\n\nThat's a different pattern, and an honest trade-off: the darkness went to the ends instead of the middle. So say exactly this and no more: **no organized band across the belly**. Not \"no dark anywhere\".\n\n## The stress test\n\nOne good picture could be luck: the right room, the right angle. So we push the Marquise as hard as our tools allow.\n\n**Ten rooms.** Photo studio, Shopping center, Home and Cloudy day below, and the other six too. No band in any of the eight that are bright enough to judge. At Home and in the Restaurant, the whole stone is darker because the room is darker. But the middle stays with the rest. (Club and UV lamp are too dark for either stone.)\n\n![The Marquise face up under Photo studio, Shopping center, Home and Cloudy day.](https://digitalgemology.com/img/learn/bt-l5-marquise-four-rooms.webp?v=ce9f8ce7)\n\nThe Marquise face up under Photo studio, Shopping center, Home and Cloudy day.\n\n**Your head.** In Brightness & Tilt, with the head shadow at its largest (30°), the Marquise drops to 47.2% under ISO, still twice DG-Bowtie's 23.2%. And here GIA's head and shoulders do show up: a dark cross of separate facets appears in the Marquise's middle. That's your head reflected, the blue of its light map, and it fades as the head gets smaller (57.1% at 20°, 70.6% at 0°). By GIA's own description, that's a bow-tie of the head-and-shoulders kind. Under a head this big, every stone shows some. It's a pattern, not a band of leakage: the Marquise's Brightness & Tilt leakage stays at 22.1%.\n\n![Brightness & Tilt with the largest head shadow, 30°: the Marquise against DG-Bowtie.](https://digitalgemology.com/img/learn/bt-l5-bt-head-30.webp?v=a30e910a)\n\nBrightness & Tilt with the largest head shadow, 30°: the Marquise against DG-Bowtie.\n\n**Tilt, under the biggest head.** Keep the 30° head shadow and tip both stones from −30° to +30°. Under ISO, the Marquise stays between 41.0% and 50.7% at every tilt. DG-Bowtie stays between 19.9% and 35.2%. The dark cross moves as the Marquise tips, and it breaks up at other angles. It's the head's reflection, not something fixed in the stone. And no band of leakage opens across its belly at any tilt.\n\nThe video at the top of [our tilt and head-shadow page](https://digitalgemology.com/learn/bow-tie/bow-tie-tilt-and-head-shadow) shows this sweep.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the **Marquise**, view **Face up**, **Light map** on. Find the belly. What color is it?\n2. Switch to the **Oval**. Where does its black sit?\n3. Turn the light map off and take the Marquise through all ten lightings.\n4. Open [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis) with the Marquise against DG-Bowtie. Set **Head shadow** to 30°, then drag **Tilt** from −30° to +30°.\n5. **The break-it challenge:** find any setting, in either tool, that puts an organized band of black across the Marquise's belly.\n\n## What the stress test shows\n\nThe Marquise has no band across its belly. Its belly is the reddest part of its map, and it out-shines DG-Bowtie (brilliance 64 against 27). The Oval has no band across its belly either. Its darkness sits at the ends. In every room we tried, under every head shadow and at every tilt, the Marquise stays well above DG-Bowtie. The head never changes its leakage.\n\nThe largest head shadow paints a cross of contrast into the Marquise's middle: the head-and-shoulders reflection GIA describes. It moves and breaks up as the stone tilts. So here's what held and what didn't. Your head's reflection is real, and it shows in every stone under a big enough head. But a band of leakage across the belly, the dark bar DG-Bowtie carries in every room, isn't \"always\" there. It's avoidable, even in the hardest shape.\n\n## Key points\n\n- GIA's oval guide and Estate Diamond Jewelry say some degree of bow-tie is always present. GIA's marquise guide calls it typical, and the NDC calls it almost inevitable.\n- One stone that doesn't fit is enough to test a claim about every stone. Our Marquise and our Oval have no organized band across the belly.\n- The Marquise is brighter than DG-Bowtie, not duller: brilliance 64 against 27.\n- Under a very large head shadow, your head shows as a contrast pattern in the middle. That is the kind of bow-tie GIA's marquise guide describes. It moves as the stone tilts, and it isn't a band of leakage.\n- Say \"no organized band of leakage across the belly\", never \"no dark anywhere\".\n\n## Sources\n\n- GIA 4Cs, *Oval Cut Diamond Guide*, 23 September 2025: minimize, \"always present\"; no overall cut grade except for round brilliants; visibility varies within the same ratio.\n- GIA 4Cs, marquise diamond guide, 29 November 2016: \"typically\" some degree; without one, \"usually lack brightness\"; the bow-tie as a reflection of your head and shoulders.\n- Grant Mobley, \"The Bow Tie Effect in Diamonds: What It Is and Why It Shouldn't Scare You\", Only Natural Diamonds (Natural Diamond Council), 31 March 2026: \"almost inevitable in elongated cuts\".\n- Benjamin Khordipour, diamond bow-tie effect guide, Estate Diamond Jewelry, updated 15 April 2026: every brilliant except the round.\n\n**Go further:** the [Oval cut page](https://digitalgemology.com/cuts/oval) has its specifications and scores, for comparing with the Marquise.\n\n## Try it free\n\n- [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis): Face-up brightness under four standard lights, and how it holds as the stone tilts.\n- [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel): Compare brilliance, fire and scintillation of two cuts, or one cut in two stones.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\n1. Why is one stone enough to test the claim \"some degree is always present\"?\n  1. Because one stone is a big sample\n  2. Because a claim about every stone fails if one stone doesn't fit\n  3. It isn't enough\n  ### Show the answer\n  **b**: \"always\" fails on one counterexample.\n2. Where does our Oval's darkness collect?\n  1. Across the belly\n  2. At its two ends\n  3. Nowhere\n  ### Show the answer\n  **b**: Two patches at the ends; the belly is clean.\n3. Under a 30° head shadow, a dark cross appears in the Marquise's middle. What is it?\n  1. Leakage\n  2. A bow-tie of black\n  3. Your head, reflected as contrast\n  ### Show the answer\n  **c**: Contrast, the blue of the light map: the head-and-shoulders kind GIA describes; its Brightness & Tilt leakage stays 22.1%.\n4. GIA's marquise guide says marquises without a bow-tie usually lack brightness. What do the Wheel's brilliance figures say for our pair?\n  ### Show the answer\n  The Marquise, without a band, has 64; DG-Bowtie, with one, has 27.\n5. Did you find a setting that puts a band across the Marquise's belly? Describe what you tried.\n  ### Show the answer\n  Open answer.\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [Marquise Cut](https://digitalgemology.com/cuts/marquise): 3D files and cutting files, €9.99 each\n- [Oval Cut](https://digitalgemology.com/cuts/oval): 3D files and cutting files, €9.99 each\n- [DG-Bowtie Cut](https://digitalgemology.com/cuts/dg-bowtie): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Bow-ties and grading reports: what the numbers can't tell you](https://digitalgemology.com/learn/bow-tie/bow-tie-and-the-grading-report)\n- [Try another topic · Historic diamond cuts: the history of the brilliant: Old mine cut diamonds: tidier, not brighter](https://digitalgemology.com/learn/historic-cuts/old-mine-cut-diamond)\n\n[Previous lesson](https://digitalgemology.com/learn/bow-tie/what-causes-a-bow-tie) · [The bow-tie effect: all lessons](https://digitalgemology.com/learn/bow-tie) · [All topics](https://digitalgemology.com/learn)"},{"id":"BT-L6","course":"The bow-tie files","lesson_number":6,"title":"Bow-ties and grading reports: what the numbers can't tell you","url":"https://digitalgemology.com/learn/bow-tie/bow-tie-and-the-grading-report","path":"/learn/bow-tie/bow-tie-and-the-grading-report","markdown":"https://digitalgemology.com/learn/bow-tie/bow-tie-and-the-grading-report.md","summary":"Does a GIA report show a bow-tie? No. What polish, symmetry, the ratio and depth can't tell you, and which documents do check for one.","queries":["bow tie gia report","does gia grade bow tie","length to width ratio bow tie"],"quiz":null,"tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/dg-bowtie","https://digitalgemology.com/cuts/marquise"],"text":"[The bow-tie effect](https://digitalgemology.com/learn/bow-tie) · 6 min read\n\n# Bow-ties and grading reports: what the numbers can't tell you\n\nA GIA report gives an oval, pear or marquise no cut grade and says nothing about a bow-tie. Polish, symmetry, the ratio and the depth can't predict one either; IGI's optional fancy-shape cut grade checks for bow-ties, and the AGS Ideal Report's ASET map covers some ovals.\n\n## Three shortcuts\n\nA marquise without a bow-tie exists: [our Marquise is one](https://digitalgemology.com/learn/bow-tie/is-a-bow-tie-always-present), while [DG-Bowtie](https://digitalgemology.com/cuts/dg-bowtie), with the same outline, has a band. So how would a buyer find one without our tools? Guides usually offer three shortcuts: **the finish grades**, **the report** and **the numbers**. Let's test all three.\n\n## Shortcut 1: Excellent polish and symmetry\n\nTwo of our sources recommend the finish grades:\n\n- **Estate Diamond Jewelry**, on reading the report: if polish and symmetry are both \"excellent\", \"you should have nothing to worry about\".\n- **Ritani**: \"Always choose an oval cut with Excellent symmetry and polish grades.\" Just before that, the same guide notes that grading labs don't give fancy shapes a cut grade. It also says a report \"won't specify whether or not it has a bow tie\".\n\nWhat do the two grades measure? In the simulator's own words:\n\n- **Polish:** how smooth the facets are. Rougher facets scatter light and look hazy.\n- **Symmetry:** how exactly the facets are placed and aligned. Misaligned facets break up the pattern.\n\nBoth are about finish and precision. Neither says where the facets point. So let's put the worst finish on the good stone and the best finish on the banded one.\n\n![DG-Bowtie with Excellent polish and symmetry beside the Marquise with Poor polish and Poor symmetry, light maps.](https://digitalgemology.com/img/learn/bt-l6-polish-symmetry-light-maps.webp?v=b24ede85)\n\nDG-Bowtie with Excellent polish and symmetry beside the Marquise with Poor polish and Poor symmetry, light maps.\n\nDG-Bowtie, Excellent and Excellent: the band is there, 59% leakage. The [Marquise](https://digitalgemology.com/cuts/marquise), Poor and Poor: its pattern is scrambled, and leakage rises a little, from 25% to 29%. But there's still no band across the belly. That small rise comes from symmetry's tilted facets. Polish doesn't change the light map at all: in the simulator, poor polish is a loss of contrast laid over the picture. Symmetry nudges the light. The angles decide it.\n\n![The same pair face up at Home.](https://digitalgemology.com/img/learn/bt-l6-polish-symmetry-home.webp?v=58668964)\n\nThe same pair face up at Home.\n\nThat doesn't make good finish grades worthless. They're part of the entry ticket for the documents below. IGI's fancy-shape cut grade first requires Very Good or better, and the AGS Ideal Report requires Excellent. But they can't see a bow-tie.\n\n## Shortcut 2: the report\n\nGIA gives an overall cut grade only to standard round brilliants. On a GIA report for a marquise, pear or oval, there's no cut grade and no word about a bow-tie. Our sources agree on that.\n\nBut that isn't the whole story. Two other documents do look:\n\n- **IGI's fancy-shape cut grade**, an option. To earn Excellent, a fancy shape must pass four steps in turn. The third step is a set of \"shape specific requirements designed to analyze bow-ties\" and other features.\n- **The AGS Ideal Report by GIA**, a light performance supplement to a GIA report, with an ASET map. The ASET map is the same kind of four-color picture as our light map. GIA offers the report only for some facet arrangements of the oval, cushion, emerald, radiant, princess and fancy round. The stone needs Excellent polish and symmetry, and it must reach the top light performance grade, AGS Ideal 0. The report comes with or without the map, so ask for the map. Marquises and pears aren't on the list.\n\nSo for an oval, you can ask whether it has an AGS Ideal Report with the map. If that report exists, it is already a good sign, because a stone with a strong band wouldn't qualify. For a marquise or a pear, ask whether the stone has an IGI fancy-shape cut grade. Or judge it with your own eyes, with [our bench routine](https://digitalgemology.com/learn/bow-tie/how-to-check-a-diamond-for-a-bow-tie).\n\n## Shortcut 3: the numbers\n\n**The ratio.** GIA's oval guide says many people prefer 1.30 to 1.50. Its own example of a noticeable bow-tie is 1.48 to 1, inside that range. GIA also notes that bow-tie visibility varies between stones with the same ratio. Our pair shows the point as plainly as possible: DG-Bowtie and the Marquise are both 2.06 to 1. Same ratio, one band.\n\n**The depth.** Ritani gives an ideal oval depth of 58–62% and a table of 53–63%. Depth is the height from table to culet, as a percentage of the width. It adds three things together: the crown's height, the girdle and the pavilion's depth. Two stones with the same total depth can share it differently between crown and pavilion. Then their belly angles differ.\n\nDepth does flag DG-Bowtie: at 93.8% it's far from any range. But a range can't see the belly. Our Oval sits at 64.0%, outside Ritani's 58–62%, and has a [clean belly](https://digitalgemology.com/learn/bow-tie/is-a-bow-tie-always-present). The range is a fair first filter, not a verdict.\n\n**The pavilion angle.** DG-Bowtie's cut page lists its \"Pavilion angle (main)\" as 42.0°. That looks like a round's: the T73 uses 40.75°. But an elongated stone has a [whole spread of pavilion angles](https://digitalgemology.com/learn/bow-tie/which-diamond-shapes-have-a-bow-tie), and the main tier is only one of them. DG-Bowtie's belly facets sit at 52.0° to 53.5°. One number hides the one that matters.\n\n|  | DG-Bowtie | Marquise |\n| --- | --- | --- |\n| Length to width | 2.06 | 2.06 |\n| Total depth | 93.8% | 62.0% |\n| Pavilion angle (main), cut page | 42.0° | 31.4° |\n| Belly pavilion facets, cutting file | 52.0°–53.5° | 41.0°–42.5° |\n| Band across the belly | yes | no |\n\nIf you read the third row alone, you'd pick the wrong stone: 42.0° looks ideal and 31.4° looks shallow. The fourth row decides, and it lives in the cutting file, not in a report.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with DG-Bowtie, **Light map** on. Leave **Polish** and **Symmetry** at **Ex**.\n2. Switch to the **Marquise** and set **Polish** and **Symmetry** to **P**. What happens to the band? What happens to the leakage figure?\n3. Open the [DG-Bowtie cut page](https://digitalgemology.com/cuts/dg-bowtie) and the [Marquise cut page](https://digitalgemology.com/cuts/marquise). Compare their specifications line by line.\n4. **The spot-the-band challenge:** using only the cut pages' specifications, without the pictures, which line would you trust to predict the band? Which lines would fool you?\n\n## What the simulator and the cut pages show\n\nDG-Bowtie with Excellent polish and symmetry has the band. The Marquise with Poor polish and symmetry doesn't (leakage 25% → 29%, the pattern scrambled, the belly clean). The finish grades can't see a bow-tie.\n\nGIA's report doesn't grade a fancy shape's cut. But IGI's optional fancy-shape cut grade checks bow-ties, and the AGS Ideal supplement shows an ASET map for some ovals. Both stones are 2.06 to 1. Depth flags DG-Bowtie's extreme 93.8%, but a range can't see the belly. The single \"main\" pavilion angle points the wrong way. The belly angles in the cutting file point the right way.\n\n## Key points\n\n- Polish grades smoothness. Symmetry grades placement. Neither says where the facets point, so neither predicts a bow-tie.\n- GIA's report gives no cut grade to fancy shapes and doesn't mention bow-tie. IGI's optional fancy-shape cut grade checks for bow-ties. The AGS Ideal Report by GIA adds an ASET map for some ovals.\n- The ratio can't tell two stones apart: both of ours are 2.06 to 1, and GIA's own noticeable example is 1.48 to 1.\n- Depth adds three heights into one number. It catches extremes but can't see the belly angle.\n- A single \"pavilion angle\" hides the spread. The belly angles decide, and they're in the cutting file.\n\n## Sources\n\n- Benjamin Khordipour, diamond bow-tie effect guide, Estate Diamond Jewelry, updated 15 April 2026: both Excellent, \"nothing to worry about\".\n- Kristin P, \"What is a bow tie in an oval diamond\", Ritani, 13 October 2025: \"Always choose\" Excellent symmetry and polish; no cut grade for fancy shapes; ideal table and depth.\n- GIA 4Cs, *Oval Cut Diamond Guide*, 23 September 2025: overall cut grade only for round brilliants; 1.30 to 1.50; the 1.48 example; visibility varies within the same ratio.\n- IGI, *Diamond Cut Grading* (igi.org): the four steps of the fancy-shape cut grade.\n- GIA, *Introducing the AGS Ideal Report by GIA*, and the GIA training module *AGS Ideal Report*, 2024: eligible shapes, ASET map.\n\n**Go further:** [How to read a diamond grading report, start to finish](https://digitalgemology.com/learn/grading-reports/how-to-read-a-diamond-grading-report) explains every line of a report, including what's printed for fancy shapes.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\n1. What does a symmetry grade measure?\n  1. How much light the stone returns\n  2. How exactly the facets are placed and aligned\n  3. Where the facets point\n  ### Show the answer\n  **b**: Placement and alignment, not direction.\n2. DG-Bowtie has Excellent polish and symmetry. Does it have a bow-tie?\n  1. No, Excellent finish rules it out\n  2. Yes: the finish grades don't see where the facets point\n  3. Only in dim light\n  ### Show the answer\n  **b**: The band is set by the angles.\n3. Which document checks for bow-ties as part of a grade?\n  1. GIA's diamond grading report\n  2. IGI's optional fancy-shape cut grade\n  3. None at all\n  ### Show the answer\n  **b**: Step 3 includes requirements designed to analyze bow-ties. (The AGS Ideal supplement shows an ASET map for some ovals.)\n4. Two marquises are both 2.06 to 1. One has a bow-tie. What does that tell you about the ratio?\n  ### Show the answer\n  The ratio can't predict it: same ratio, different bellies.\n5. DG-Bowtie's cut page lists a main pavilion angle of 42.0°. Why doesn't that number warn you about its band?\n  ### Show the answer\n  It's one tier out of a spread. The belly facets, at 52.0°–53.5°, decide, and they're only in the cutting file.\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [DG-Bowtie Cut](https://digitalgemology.com/cuts/dg-bowtie): 3D files and cutting files, €9.99 each\n- [Marquise Cut](https://digitalgemology.com/cuts/marquise): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Why bow-ties are still cut: weight, outline and cost](https://digitalgemology.com/learn/bow-tie/why-cutters-leave-a-bow-tie)\n- [Try another topic · Historic diamond cuts: the history of the brilliant: Old European cut diamonds: when the outline went round](https://digitalgemology.com/learn/historic-cuts/old-european-cut-diamond)\n\n[Previous lesson](https://digitalgemology.com/learn/bow-tie/is-a-bow-tie-always-present) · [The bow-tie effect: all lessons](https://digitalgemology.com/learn/bow-tie) · [All topics](https://digitalgemology.com/learn)"},{"id":"BT-L7","course":"The bow-tie files","lesson_number":7,"title":"Why bow-ties are still cut: weight, outline and cost","url":"https://digitalgemology.com/learn/bow-tie/why-cutters-leave-a-bow-tie","path":"/learn/bow-tie/why-cutters-leave-a-bow-tie","markdown":"https://digitalgemology.com/learn/bow-tie/why-cutters-leave-a-bow-tie.md","summary":"Why are bow-ties still cut in ovals and marquises? A deep belly keeps carats, and diamonds are sold by weight. The trade-off in size and price.","queries":["why do oval diamonds have a bow tie","bow tie and carat retention"],"quiz":null,"tools":["https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/marquise","https://digitalgemology.com/cuts/dg-bowtie"],"text":"[The bow-tie effect](https://digitalgemology.com/learn/bow-tie) · 4 min read\n\n# Why bow-ties are still cut: weight, outline and cost\n\nMany long stones keep a bow-tie because a deep belly keeps weight, and diamonds are sold by the carat. At 1.00 ct, our band-free Marquise has 31% more face-up area than the deep DG-Bowtie; to look as big, DG-Bowtie must weigh 1.50 ct.\n\n## A fair question\n\nA bow-tie across the belly [can be avoided](https://digitalgemology.com/learn/bow-tie/is-a-bow-tie-always-present), even in a marquise. And [the paperwork rarely catches one](https://digitalgemology.com/learn/bow-tie/bow-tie-and-the-grading-report). So why are so many long stones still cut with one?\n\nFor the deep kind, like the band in our [DG-Bowtie](https://digitalgemology.com/cuts/dg-bowtie) marquise, the answer is **weight**.\n\n## Same weight, different size\n\nPut DG-Bowtie beside our [Marquise](https://digitalgemology.com/cuts/marquise), which has the same outline and facets but no band. Set both to the same weight, 1.00 ct each, in the Shopping center light.\n\n![DG-Bowtie and the Marquise at 1.00 ct each, face up under Shopping center lighting, at true size.](https://digitalgemology.com/img/learn/bt-l7-same-weight.webp?v=6862a653)\n\nDG-Bowtie and the Marquise at 1.00 ct each, face up under Shopping center lighting, at true size.\n\n| 1.00 ct diamond | Length × width × depth |\n| --- | --- |\n| DG-Bowtie | 9.13 × 4.43 × 4.16 mm |\n| Marquise | 10.47 × 5.08 × 3.15 mm |\n\nThe Marquise is 15% longer and has 31% more face-up area, for the same carats. DG-Bowtie hides its weight underneath, in a pavilion so deep that the stone is 93.8% as deep as it is wide. (Notice its belly in this shop light: pale and glassy, not dark. [The room explains why](https://digitalgemology.com/learn/bow-tie/bow-tie-tilt-and-head-shadow).)\n\n## Same size, different weight\n\nNow turn it around. Set DG-Bowtie to 1.50 ct and leave the Marquise at 1.00 ct.\n\n![DG-Bowtie at 1.50 ct beside the Marquise at 1.00 ct: the same face-up size.](https://digitalgemology.com/img/learn/bt-l7-same-size.webp?v=1d873a86)\n\nDG-Bowtie at 1.50 ct beside the Marquise at 1.00 ct: the same face-up size.\n\n| Diamond | Carat | Length × width |\n| --- | --- | --- |\n| DG-Bowtie | 1.50 ct | 10.45 × 5.07 mm |\n| Marquise | 1.00 ct | 10.47 × 5.08 mm |\n\nFace up, they're the same stone, to a few hundredths of a millimeter. One weighs half as much again as the other.\n\nWeight follows the cube of size, so you can work out the other direction too. A Marquise with the face-up size of a 1.00 ct DG-Bowtie weighs (9.13 ÷ 10.47)³ × 1.00 ≈ **0.66 ct**. The deep cut reaches the one-carat line. The light cut doesn't.\n\n## Why that decides so much\n\nDiamonds are sold by weight. GIA's retailer training notes two things about how that works. Prices rise faster than weight, because larger diamonds are rarer. And round weights (a half, three quarters, one carat) carry a price step that the eye can't see.\n\nSo picture a cutter with a piece of rough. A deeper pavilion keeps more of the crystal as weight, and it can carry the stone over the one-carat line. A lighter, brighter cut gives up that weight to put angles where the light needs them.\n\nThe rough shapes the design in other ways too. GIA's oval guide notes that ovals longer than 1.50 to 1 are rarely seen because they're impractical to cut from diamond crystals.\n\nNone of this is hidden or dishonest. A buyer who wants the most carats for the money gets them in a deep stone. A buyer who wants the brightest stone for its weight wants the other one. When a bow-tie comes from a deep belly, as DG-Bowtie's does, it comes with the weight. **It's a trade-off made at the wheel, not a law of optics.**\n\n(Not every bow-tie is a weight choice. GIA's marquise guide notes they're common in shallow pavilions too, and a shallow stone carries less weight, not more.)\n\nAnd removing it does cost something. The Natural Diamond Council's article says that trying to eliminate a bow-tie entirely \"can lead to compromises elsewhere in the stone\". That's fair, and [our rebuild](https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie) names exactly what it cost our Marquise.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with DG-Bowtie at **1.00 ct**, view **Face up**, lighting **Shopping center**. Note its measurements in the report.\n2. Switch to the **Marquise** at 1.00 ct. Which looks bigger? By how much?\n3. Set DG-Bowtie to **1.5 ct**. Compare its measurements with the Marquise at 1.00 ct.\n4. **The price-tag challenge:** give both stones the same price per carat (any figure you like). What does each cost? Which would you rather wear, and which would a seller rather sell?\n\n## What the simulator shows\n\nAt 1.00 ct each, the Marquise is 10.47 × 5.08 mm and DG-Bowtie 9.13 × 4.43 mm: 31% more face-up area for the same weight. To look as big as the 1.00 ct Marquise, DG-Bowtie must weigh 1.50 ct. A Marquise as big as a 1.00 ct DG-Bowtie weighs only 0.66 ct, below the one-carat line. Give both the same price per carat. Of the two stones that look identical in size, the deep one costs 1.5 times as much. The extra money buys the band.\n\nDG-Bowtie is an extreme case: 93.8% deep. Real stones sit anywhere between the two. The trade-off points the same way: a steeper belly keeps more weight.\n\n## Key points\n\n- At the same weight, the Marquise has 31% more face-up area than DG-Bowtie.\n- At the same face-up size, DG-Bowtie weighs 1.5 times as much (1.50 ct against 1.00 ct).\n- Weight follows the cube of size: a Marquise the size of a 1.00 ct DG-Bowtie weighs about 0.66 ct.\n- Diamonds are sold by weight. Prices rise faster than weight, and round weights carry a price step. A deep belly keeps carats.\n- A bow-tie from a deep belly is a trade-off made at the wheel, not a law of optics.\n\n## Sources\n\n- GIA, Retailer Training Modules, module 2 (2023): larger diamonds are rarer, so prices rise more steeply; round \"magic\" weights.\n- GIA 4Cs, *Oval Cut Diamond Guide*, 23 September 2025: ovals above 1.50 to 1 are rarely seen, being impractical to cut from diamond crystals.\n- Grant Mobley, \"The Bow Tie Effect in Diamonds: What It Is and Why It Shouldn't Scare You\", Only Natural Diamonds (Natural Diamond Council), 31 March 2026: trying to eliminate a bow-tie entirely \"can lead to compromises elsewhere in the stone\".\n\n**Go further:** [Carat weight vs size](https://digitalgemology.com/learn/four-cs/carat-weight-vs-size) explains carat weight, size and the magic weights.\n\n## Try it free\n\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\n1. At 1.00 ct each, which marquise looks bigger face up?\n  1. DG-Bowtie\n  2. The Marquise\n  3. They look the same\n  ### Show the answer\n  **b**: 31% more face-up area for the same weight.\n2. To look as big as the 1.00 ct Marquise, what must DG-Bowtie weigh?\n  1. 1.00 ct\n  2. 1.25 ct\n  3. 1.50 ct\n  ### Show the answer\n  **c**: 1.50 ct gives 10.45 × 5.07 mm, the Marquise's size at 1.00 ct.\n3. Why would a cutter keep a deep belly?\n  1. It always looks brighter\n  2. It keeps more of the rough as weight, which is what diamonds are sold by\n  3. Labs require it\n  ### Show the answer\n  **b**: Weight is what's paid for, and a deep pavilion keeps it.\n4. A Marquise is cut to the face-up size of a 1.00 ct DG-Bowtie. Roughly what does it weigh, and why does that matter at the counter?\n  ### Show the answer\n  About 0.66 ct, below the one-carat line, where round weights carry a price step.\n5. In the price-tag challenge, what did your two stones cost at the same price per carat?\n  ### Show the answer\n  Open answer: the same-looking DG-Bowtie costs 1.5 times as much.\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [Marquise Cut](https://digitalgemology.com/cuts/marquise): 3D files and cutting files, €9.99 each\n- [DG-Bowtie Cut](https://digitalgemology.com/cuts/dg-bowtie): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: Fixing a bow-tie: the steep belly of DG-Bowtie](https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie)\n- [Try another topic · The four Cs of diamonds: Diamond cut grade: Excellent vs Poor, side by side](https://digitalgemology.com/learn/four-cs/diamond-cut-grade-excellent-vs-poor)\n\n[Previous lesson](https://digitalgemology.com/learn/bow-tie/bow-tie-and-the-grading-report) · [The bow-tie effect: all lessons](https://digitalgemology.com/learn/bow-tie) · [All topics](https://digitalgemology.com/learn)"},{"id":"BT-L8","course":"The bow-tie files","lesson_number":8,"title":"Fixing a bow-tie: the steep belly of DG-Bowtie","url":"https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie","path":"/learn/bow-tie/how-to-fix-a-bow-tie","markdown":"https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie.md","summary":"How to fix a bow-tie in a marquise: in diamond, belly facets past 51.9° let head-on light out of the back. We lowered them, and show what it cost.","queries":["bow tie free marquise","how to avoid bow tie","marquise cut bow tie"],"quiz":null,"tools":["https://digitalgemology.com/tools/brightness-tilt-analysis","https://digitalgemology.com/tools/cut-performance-wheel","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/dg-bowtie","https://digitalgemology.com/cuts/marquise"],"text":"[The bow-tie effect](https://digitalgemology.com/learn/bow-tie) · 7 min read\n\n# Fixing a bow-tie: the steep belly of DG-Bowtie\n\nDG-Bowtie, a marquise, has a bow-tie because its belly facets sit at 52.0°–53.5°: in diamond, past about 51.9°, head-on light leaves through the back. We rebuilt it as our Marquise, with the same outline and facets and the belly at 41.0°–42.5°: leakage fell from 59% to 25%.\n\nVideo: [Bow-tie effect explained: how the belly angle steers the light (animated)](https://www.youtube.com/watch?v=MpHBSHuo6sM)\n\nA slice across the belly. A vertical ray meets the opposite facet at 180° − 3 × the belly angle. Past 51.9°, it leaves through the back. DG-Bowtie's belly tiers (52.0° to 53.5°) against the Marquise's (41.0° to 42.5°), then both light maps and their Light Return shares. · 1 min 29 s · No sound, captions on screen\n\n## Transcript\n\nDG-Bowtie: 87 facets, 93.8% deep, and a black band across the belly.\n\nTake a slice across the belly. Follow the light that comes straight down.\n\nThe belly facets of DG-Bowtie are cut at 52.0° to 53.5°. Here: 52.3°.\n\nThe light meets the facet at 52.3°. That is far above 24.4°, the critical angle.\n\nSo the facet works as a mirror. It sends the light across to the opposite facet.\n\nThere it arrives at 180° − 3 × 52.3° = 23.1°. That is less than 24.4°.\n\nThe gray cone holds every angle below 24.4°. Light inside it gets out.\n\nSo the light goes out through the back of the stone. That facet goes dark.\n\nNow change the belly facet angle. Watch the angle at the opposite facet.\n\nThe light flips at (180° − 24.4°) ÷ 3 = 51.9°. Steeper than that, it leaks.\n\nDG-Bowtie's belly tiers: 52.0°, 52.3° and 53.5°. All three are past the limit.\n\nThe next tiers toward the points, 49.0° and 49.3°, are below it. The band stops there.\n\nThe Marquise keeps the outline and all 87 facets. Every tier is 9.5° to 11° lower.\n\nIts belly facets sit at 41.0° to 42.5°. The light meets the opposite facet at about 56°.\n\nThat is far past 24.4°. So the light reflects again and comes back up to you.\n\nLower angles make a shallower stone: 93.8% deep before, 62.0% after.\n\nReal light comes from every angle. The light map shows the full picture.\n\nLeakage falls from 59% to 25%. No organized band across the belly.\n\nThe cost: at the same face-up size, the Marquise weighs about a third less.\n\n## The starting point: DG-Bowtie\n\nA deep belly gets cut because [it keeps carats](https://digitalgemology.com/learn/bow-tie/why-cutters-leave-a-bow-tie). And the marquise is [the hardest shape to cut well](https://digitalgemology.com/learn/bow-tie/which-diamond-shapes-have-a-bow-tie). So this is the real test: take the hardest shape, with a bow-tie in it, and fix it.\n\nHere's where we start. [DG-Bowtie](https://digitalgemology.com/cuts/dg-bowtie), the first marquise in our library: 87 facets, 2.06 to 1, 93.8% deep, and a black band across the belly. Light Return: 15% direct, 21% indirect, 5% contrast, 59% leakage.\n\n![DG-Bowtie and the Marquise in profile, facet mesh on: 93.8% against 62.0% deep.](https://digitalgemology.com/img/learn/bt-l8-profiles-before-after.webp?v=0580c904)\n\nDG-Bowtie and the Marquise in profile, facet mesh on: 93.8% against 62.0% deep.\n\n## The diagnosis\n\nGIA's marquise guide notes that bow-ties are especially common in diamonds with \"either shallow or very deep pavilions\". DG-Bowtie is the very deep kind. Here's exactly what that does.\n\nTake a slice across the belly. Follow the light that comes straight down through the table.\n\n1. It meets a belly pavilion facet. DG-Bowtie's belly facets are cut at **52.0° to 53.5°**. That's far above diamond's critical angle, 24.4°. So the facet acts as a perfect mirror and sends the light across to the opposite facet.\n2. It meets the opposite belly facet. Geometry fixes the angle: it arrives 180° − 3 × 52.3° = **23.1°** from straight-on. That's **less** than 24.4°, so this time the facet doesn't reflect. The light goes straight out through the back of the stone.\n\nThe limit is easy to work out: (180° − 24.4°) ÷ 3 = **51.9°**. In diamond, a pair of belly facets steeper than about 51.9° lets head-on light out of the back on its second bounce. All three of DG-Bowtie's belly tiers are past it (52.0°, 52.3° and 53.5°). The next tiers toward the points, at 49.0° and 49.3°, are below it. That's why the band stops at the shoulders.\n\n![A slice across the belly, light straight down: at 52.3° it leaves through the opposite facet; at 41.3° it reflects twice and comes back up through the table.](https://digitalgemology.com/img/learn/bt-l8-belly-cross-section.webp?v=6a096844)\n\nA slice across the belly, light straight down: at 52.3° it leaves through the opposite facet; at 41.3° it reflects twice and comes back up through the table.\n\n(This is a simplified slice. Real light arrives from every angle, so we read the full picture from the light map. But the slice shows the heart of it.)\n\nThe animation at the top of this page shows the same slice.\n\n## What we changed\n\nWe kept everything a buyer would recognize: the outline (2.06 to 1), all 87 facets, each one in the same position around the stone. And we lowered every crown and pavilion tier, by about 9.5° to 11°.\n\n|  | DG-Bowtie | Marquise |\n| --- | --- | --- |\n| Belly pavilion facets | 52.0°–53.5° | 41.0°–42.5° |\n| Pavilion facets at the points | 41.0° | 30.5° |\n| Steepest crown facets | 54.5° | 43.6° |\n| Total depth | 93.8% | 62.0% |\n| Facets, outline | 87, 2.06 to 1 | 87, 2.06 to 1 |\n\nThe belly facets now sit at 41.0° to 42.5°, close to the T73's 40.75° and far below the 51.9° limit. Light that comes down through the table meets the opposite facet at about 56°, well past the critical angle. So it reflects again and comes back up to you. The points went shallower, to 30.5°. In diamond, that angle still reflects head-on light: the [Marquise](https://digitalgemology.com/cuts/marquise) cut page measures 100% of its pavilion holding head-on light in diamond.\n\n## The result\n\n![DG-Bowtie and the Marquise, light maps: the black band gone, the belly red.](https://digitalgemology.com/img/learn/bt-l8-light-maps-before-after.webp?v=bc1759e3)\n\nDG-Bowtie and the Marquise, light maps: the black band gone, the belly red.\n\n| 1.00 ct diamond | DG-Bowtie | Marquise |\n| --- | --- | --- |\n| Light Return (direct, indirect, contrast, leakage) | 15, 21, 5, 59% | 47, 22, 6, 25% |\n| Brilliance (Cut Performance Wheel) | 27 | 64 |\n| Fire | 82 | 89 |\n| Scintillation | 86 | 86 |\n| Brightness & Tilt ISO, head shadow 20° | 24.6% | 57.1% |\n\n![The Cut Performance Wheel, DG-Bowtie against the Marquise in diamond.](https://digitalgemology.com/img/learn/bt-l8-wheel-before-after.webp?v=7678d41b)\n\nThe Cut Performance Wheel, DG-Bowtie against the Marquise in diamond.\n\nScintillation didn't move. The Wheel reads it from the pattern of facets, and the pattern is the same. Everything that depends on the angles moved together.\n\n## The stress test\n\nA fix that only works in a good room isn't a fix. So:\n\n- **Every room.** In all eight lightings bright enough to judge, the Marquise shows no band. DG-Bowtie's band shows in every one, white or dark. (Club and UV lamp are too dark for either stone.)\n- **Your head.** At the largest head shadow, the Marquise keeps 47.2% under ISO against DG-Bowtie's 23.2%.\n- **Tilt.** With a 20° head shadow and a tilt from −30° to +30°, the tool's tilt chart keeps the Marquise between 50.8% and 58.6% under ISO. DG-Bowtie stays between 25.0% and 37.9%. (The chart uses a coarser grid than the face-up table above, so face-up figures differ by a few tenths.)\n\nVideo: [DG-Bowtie and the Marquise turning side by side at Home](https://www.youtube.com/watch?v=4lfdu144qo8)\n\nDG-Bowtie and the Marquise turning side by side at Home. · 10 s · No sound\n\nVideo: [DG-Bowtie and the Marquise tilting −30° to +30°, 20° head shadow](https://www.youtube.com/watch?v=rP3W64AczaM)\n\nBrightness & Tilt, the two stones tilting from −30° to +30° under a 20° head shadow: DG-Bowtie before, the Marquise after. · 10 s · No sound\n\n## What it cost\n\nA rebuild presented as free would be a sales pitch. Here's the bill.\n\n1. **Weight.** At the same face-up size, the Marquise [weighs a third less](https://digitalgemology.com/learn/bow-tie/why-cutters-leave-a-bow-tie): about 0.66 ct where DG-Bowtie weighs 1.00 ct. That's the \"compromise elsewhere\" the Natural Diamond Council warns about, and it's real.\n2. **It's a diamond fix.** The Marquise's lower angles are matched to diamond. Amethyst has a critical angle of 40.4°. In amethyst, the shallower facets toward the points let head-on light straight out on the first bounce. Large windows open at both ends (Light Return 28/5/10/57). Its belly facets, at 41.0°–42.5°, still just hold. Its cut page advises a steeper pavilion for ruby, sapphire, emerald and amethyst. (DG-Bowtie in amethyst is worse still: 75% leakage.)\n3. **Scatter remains.** The Marquise still leaks 25%, in scattered facets and toward the points. So we say **no organized band across the belly**, never \"no dark at all\".\n4. **The points are as sharp as before.** Same outline, same points, so they still need protection in a setting, usually with V-prongs.\n\n![The Marquise in diamond, the Marquise in amethyst and DG-Bowtie in amethyst, light maps.](https://digitalgemology.com/img/learn/bt-l8-amethyst-cost.webp?v=bad695f2)\n\nThe Marquise in diamond, the Marquise in amethyst and DG-Bowtie in amethyst, light maps.\n\n## The short version\n\n> The bow-tie is always in the stone. It is only sometimes on your finger.\n\nThe room decides **when you see it**. The angles decide **whether it's there**. So we changed the angles.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with DG-Bowtie, **Light map** on, then the Marquise. Read both Light Return bars.\n2. Open [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel) with DG-Bowtie against the Marquise. Which axis didn't move?\n3. Open [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis) with DG-Bowtie against the Marquise, **Head shadow** 20°. Drag **Tilt** from −30° to +30°.\n4. Back in the simulator, set the Marquise to **Amethyst**, light map on. What came back?\n5. **The cutter's challenge:** work out the deep limit for belly facets in moissanite (critical angle 22.2°) and in cubic zirconia (27.7°), using (180° − critical angle) ÷ 3.\n\n## What the tools show\n\nDG-Bowtie's belly facets, at 52.0° to 53.5°, are just past diamond's 51.9° limit. So head-on light leaves through the opposite facet: the black band. The Marquise keeps the outline and all 87 facets. It lowers every tier by about 9.5° to 11° and puts the belly at 41.0° to 42.5°. Leakage falls from 59% to 25%, brilliance rises from 27 to 64, and fire from 82 to 89. The band of leakage is gone in every room bright enough to judge, under every head shadow and at every tilt.\n\nThe cost: a third less weight at the same face-up size, a cut matched to diamond only, and scatter that remains. In the challenge: about 52.6° in moissanite and 50.8° in cubic zirconia.\n\n## Key points\n\n- DG-Bowtie's belly facets sit at 52.0°–53.5°. In diamond, when they pass about 51.9°, head-on light leaves through the opposite facet: that's the band.\n- The fix kept the outline, the 87 facets and their positions. It lowered every tier by about 9.5° to 11°. Belly facets now sit at 41.0°–42.5°.\n- Leakage 59% → 25%, brilliance 27 → 64, fire 82 → 89, scintillation unchanged.\n- No band of leakage in any of the eight lightings bright enough to judge, at any head shadow or tilt.\n- The costs: a third less weight at the same size, a diamond-only fix (windows open at the ends in amethyst), and scatter that remains. A bow-tie is a decision, and it can be decided differently.\n\n## Sources\n\n- GIA 4Cs, marquise diamond guide, 29 November 2016: bow-ties especially common with shallow or very deep pavilions.\n- Grant Mobley, \"The Bow Tie Effect in Diamonds: What It Is and Why It Shouldn't Scare You\", Only Natural Diamonds (Natural Diamond Council), 31 March 2026: removing it entirely \"can lead to compromises elsewhere in the stone\".\n\n**Go further:** both stones' cutting files and 3D models are on the [Marquise](https://digitalgemology.com/cuts/marquise) and [DG-Bowtie](https://digitalgemology.com/cuts/dg-bowtie) cut pages.\n\n## Try it free\n\n- [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis): Face-up brightness under four standard lights, and how it holds as the stone tilts.\n- [Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel): Compare brilliance, fire and scintillation of two cuts, or one cut in two stones.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\n1. Why does light leave through the back of DG-Bowtie's belly?\n  1. The facets are badly polished\n  2. After one reflection it meets the opposite belly facet at less than the critical angle\n  3. The table is too large\n  ### Show the answer\n  **b**: 180° − 3 × 52.3° = 23.1°, less than 24.4°.\n2. What is diamond's deep limit for a pair of belly facets, for light coming straight down?\n  1. About 40.75°\n  2. About 51.9°\n  3. About 60°\n  ### Show the answer\n  **b**: (180° − 24.4°) ÷ 3.\n3. What did the rebuild keep, and what did it change?\n  ### Show the answer\n  It kept the outline, the 87 facets and their positions; it lowered every crown and pavilion tier by about 9.5° to 11°.\n4. Why didn't scintillation change on the Wheel?\n  ### Show the answer\n  It's read from the pattern of facets, and the pattern is the same.\n5. Name two costs of the fix, with a number for each.\n  ### Show the answer\n  Any two: about 0.66 ct instead of 1.00 ct at the same face-up size; in amethyst, windows open at the ends (57% leakage); 25% scatter remains.\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [DG-Bowtie Cut](https://digitalgemology.com/cuts/dg-bowtie): 3D files and cutting files, €9.99 each\n- [Marquise Cut](https://digitalgemology.com/cuts/marquise): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Next lesson: How to check a stone for a bow-tie: a bench routine](https://digitalgemology.com/learn/bow-tie/how-to-check-a-diamond-for-a-bow-tie)\n- [Try another topic · Historic diamond cuts: the history of the brilliant: Tolkowsky's 1919 ideal cut: the brilliant that was calculated](https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919)\n\n[Previous lesson](https://digitalgemology.com/learn/bow-tie/why-cutters-leave-a-bow-tie) · [The bow-tie effect: all lessons](https://digitalgemology.com/learn/bow-tie) · [All topics](https://digitalgemology.com/learn)"},{"id":"BT-L9","course":"The bow-tie files","lesson_number":9,"title":"How to check a stone for a bow-tie: a bench routine","url":"https://digitalgemology.com/learn/bow-tie/how-to-check-a-diamond-for-a-bow-tie","path":"/learn/bow-tie/how-to-check-a-diamond-for-a-bow-tie","markdown":"https://digitalgemology.com/learn/bow-tie/how-to-check-a-diamond-for-a-bow-tie.md","summary":"How to check a diamond for a bow-tie before you buy: a bench routine from a dim room to the light map, run on an oval, a pear and a teardrop.","queries":["how to check bow tie diamond","spot a bow tie before buying"],"quiz":null,"tools":["https://digitalgemology.com/tools/brightness-tilt-analysis","https://digitalgemology.com/tools/3d_gemstone_simulator"],"cuts":["https://digitalgemology.com/cuts/oval","https://digitalgemology.com/cuts/pear","https://digitalgemology.com/cuts/teardrop","https://digitalgemology.com/cuts/dg-bowtie","https://digitalgemology.com/cuts/marquise"],"text":"[The bow-tie effect](https://digitalgemology.com/learn/bow-tie) · 5 min read\n\n# How to check a stone for a bow-tie: a bench routine\n\nTo check a stone for a bow-tie, look at it face up in a dim room with your head over it, and rock it. Then ask for a video and for an AGS Ideal ASET map or an IGI fancy-shape cut grade; with the stone's file, read its light map.\n\n## From our stone to yours\n\n[Our rebuild of a bow-tie marquise](https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie) ends on one rule: the room decides when you see a bow-tie, and the angles decide whether it's there. That gives you two kinds of check. Some use the room to make a band show if there is one. Others go straight to the angles.\n\nHere's the routine, from free and quick to thorough.\n\n## The routine\n\n**1. Look in the wrong light.** Shop light is made to show stones at their best. [It can turn a band pale or even white](https://digitalgemology.com/learn/bow-tie/bow-tie-tilt-and-head-shadow). So look at the stone face up somewhere dim, with your head over it, like our Home lighting. If there's a band, that's when it shows.\n\n**2. Rock it.** Tip the stone slowly from side to side. If a band stays across the belly as the stone moves, it is in the stone. In [our stress test](https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie), with a 20° head shadow, [DG-Bowtie](https://digitalgemology.com/cuts/dg-bowtie) (a marquise with a strong band) was darkest face up, the view you look at most.\n\n**3. Ask for a video.** If you can't see the stone yourself, ask for one. GIA's oval guide gives the same advice, because stones with the same ratio can look different.\n\n**4. Ask what paperwork exists.** A GIA grading report won't mention a bow-tie. But some ovals have an AGS Ideal Report by GIA. GIA issues it only to stones at its top light performance grade, so if one exists, that is a good sign. Ask for the version with the ASET map, where leakage shows in gray. And [IGI's optional cut grade for fancy shapes](https://digitalgemology.com/learn/bow-tie/bow-tie-and-the-grading-report) checks bow-ties as one of its steps.\n\n**5. Load the file.** If you have the stone's cutting file or 3D model (as a cutter, a designer or a file buyer), load it into our tools with **Measure your own stone**. The 3D Gemstone Simulator, Brightness & Tilt and the Cut Performance Wheel all take it. They read GemCad (.asc, .gem), Gem Cut Studio, STL, OBJ, PLY, OFF, glTF, 3MF, STEP and FBX, on your own device. The file is never uploaded. Turn on the light map and look across the belly.\n\n**6. Cutters: check the belly angles.** Take light that comes straight down. For that light, a pair of belly facets must be:\n\n- steeper than the stone's critical angle, or light goes straight through;\n- flatter than (180° − critical angle) ÷ 3, or [light leaves through the opposite facet](https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie).\n\n| Stone | Critical angle | Belly facets between |\n| --- | --- | --- |\n| Diamond | 24.4° | 24.4° and 51.9° |\n| Moissanite | 22.2° | 22.2° and 52.6° |\n| Cubic zirconia | 27.7° | 27.7° and 50.8° |\n| Amethyst | 40.4° | 40.4° and 46.5° |\n\nIt's a simplified slice, not a whole design check. But it explains a lot at a glance. Look at amethyst: a window only 6° wide. That's why a design made for diamond so often fails in a low-index stone.\n\n## Run it on three stones\n\nOur library has three more long stones: the **[Oval](https://digitalgemology.com/cuts/oval)**, the **[Pear](https://digitalgemology.com/cuts/pear)** and the **[Teardrop](https://digitalgemology.com/cuts/teardrop)**. Here's the bench run on all three.\n\n![The Oval, Pear and Teardrop, 1.00 ct each, light maps at true size.](https://digitalgemology.com/img/learn/bt-l9-three-stones-light-maps.webp?v=af55b4b9)\n\nThe Oval, Pear and Teardrop, 1.00 ct each, light maps at true size.\n\n| 1.00 ct diamond | Light Return (direct, indirect, contrast, leakage) | Where the black sits | Verdict |\n| --- | --- | --- | --- |\n| Oval | 33, 27, 3, 38% | two patches at the ends | clean belly, dark ends |\n| Pear | 35, 26, 8, 31% | scattered toward the point | clean belly, scatter |\n| Teardrop | 30, 27, 3, 40% | toward the point and along both shoulders | clean belly, scatter |\n\n![Brightness & Tilt, the Pear against the Teardrop, head shadow 20°.](https://digitalgemology.com/img/learn/bt-l9-bt-pear-vs-teardrop-head-20.webp?v=307edc2d)\n\nBrightness & Tilt, the Pear against the Teardrop, head shadow 20°.\n\nIn Brightness & Tilt with a 20° head shadow, the Pear and the Teardrop are almost level under ISO (46.3% and 46.8%). But the Teardrop leaks more (42.2% against 34.1%).\n\nNone of the three has an organized band across the belly. Each one has its own trade-off, and you can now say exactly where it is.\n\n### Try it yourself\n\n1. Open [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator) with the **Oval**, view **Face up**, lighting **Home**. Then turn on **Light map**. Repeat for the **Pear** and the **Teardrop**.\n2. Open [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis) with the Pear against the Teardrop. Set **Head shadow** to 20° and drag **Tilt**.\n3. If you have a cutting file or a 3D model of your own, drop it on either tool with **Measure your own stone**.\n4. **The challenge:** choose three elongated stones (from the library or your own files). Run the routine and rank them.\n\n## What the routine shows\n\nThe routine runs from free to thorough. Look in a dim room with your head over the stone, and rock it. Ask for a video, and ask what paperwork exists. Load the file. If you cut, check the belly angles against the stone's limits.\n\nOn our three library stones, the routine gives three clear verdicts. The Oval has a clean belly and dark ends. The Pear and the Teardrop have clean bellies and scatter toward their points. The Teardrop leaks most (40%).\n\n## Key points\n\n- Look for a bow-tie where it shows: face up in a dim room, with your head over the stone, and while you rock it.\n- Ask for a video, and ask what exists beyond the GIA report: an AGS Ideal ASET map for some ovals, or IGI's fancy-shape cut grade.\n- With the file, our tools show the band directly in the light map.\n- For light coming straight down, belly facets in diamond belong between 24.4° and 51.9°. Low-index stones have a much narrower window.\n- A clean belly isn't a perfect stone: name where the dark went.\n\n## Sources\n\n- GIA 4Cs, *Oval Cut Diamond Guide*, 23 September 2025: view the stone in person or request videos.\n- GIA, *Introducing the AGS Ideal Report by GIA*, and the GIA training module *AGS Ideal Report*, 2024: eligible shapes; ASET map, gray for leakage.\n- IGI, *Diamond Cut Grading* (igi.org): the fancy-shape cut grade's bow-tie step.\n\n**Go further:** [Use your own file](https://digitalgemology.com/about/how-we-measure/your-own-file) lists the formats our tools read, and what they check.\n\n## Try it free\n\n- [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis): Face-up brightness under four standard lights, and how it holds as the stone tilts.\n- [3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator): Turn a cut in seven gemstones and set its carat, color, clarity and cut grade.\n\nFree, in your browser, no account.\n\n## Quick quiz\n\n1. Where are you most likely to see a bow-tie, if a stone has one?\n  1. Under bright shop lights\n  2. Face up in a dim room, with your head over the stone\n  3. In a photo studio\n  ### Show the answer\n  **b**: [Bow-tie in the stone, sometimes on your finger: tilt and head shadow](https://digitalgemology.com/learn/bow-tie/bow-tie-tilt-and-head-shadow): the room decides when you see it.\n2. Which document can show a bow-tie on an oval?\n  1. The GIA grading report\n  2. The AGS Ideal Report by GIA, with its ASET map\n  3. The receipt\n  ### Show the answer\n  **b**: For eligible ovals; IGI's optional fancy-shape cut grade also checks bow-ties.\n3. In diamond, for light coming straight down, which pair of belly facet angles leaks through the opposite facet?\n  1. 41°\n  2. 49°\n  3. 53°\n  ### Show the answer\n  **c**: Past 51.9°.\n4. Why is amethyst harder to cut without dark areas than diamond?\n  ### Show the answer\n  Its critical angle (40.4°) leaves a window of about 6° for belly facets (40.4° to 46.5°), against 27.5° in diamond.\n5. Run the routine on one stone and give your verdict: band, scatter or clean belly?\n  ### Show the answer\n  Open answer.\n\n## Cuts in this lesson\n\nWe sell the files of these cuts: 3D models and cutting files, with a personal-use license.\n\n- [Oval Cut](https://digitalgemology.com/cuts/oval): 3D files and cutting files, €9.99 each\n- [Pear Cut](https://digitalgemology.com/cuts/pear): 3D files and cutting files, €9.99 each\n- [Teardrop Cut](https://digitalgemology.com/cuts/teardrop): 3D files and cutting files, €9.99 each\n- [DG-Bowtie Cut](https://digitalgemology.com/cuts/dg-bowtie): 3D files and cutting files, €9.99 each\n- [Marquise Cut](https://digitalgemology.com/cuts/marquise): 3D files and cutting files, €9.99 each\n\n## Keep exploring\n\n- [Try another topic · How to read a diamond grading report: The ID section of a diamond report: number, shape and measurements](https://digitalgemology.com/learn/grading-reports/diamond-report-identity-section)\n\n[Previous lesson](https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie) · [The bow-tie effect: all lessons](https://digitalgemology.com/learn/bow-tie) · [All topics](https://digitalgemology.com/learn)"}],"courses":[{"title":"The four Cs of diamonds","course":"The four Cs","url":"https://digitalgemology.com/learn/four-cs","lessons":["https://digitalgemology.com/learn/four-cs/the-four-cs-explained","https://digitalgemology.com/learn/four-cs/carat-weight-vs-size","https://digitalgemology.com/learn/four-cs/diamond-color-scale-d-to-z","https://digitalgemology.com/learn/four-cs/fancy-color-diamonds-and-fluorescence","https://digitalgemology.com/learn/four-cs/diamond-clarity-scale","https://digitalgemology.com/learn/four-cs/diamond-cut-grade-excellent-vs-poor","https://digitalgemology.com/learn/four-cs/how-diamond-cut-grade-is-determined","https://digitalgemology.com/learn/four-cs/which-of-the-four-cs-matters-most"]},{"title":"Diamond anatomy and proportions","course":"Anatomy of a diamond","url":"https://digitalgemology.com/learn/diamond-anatomy","lessons":["https://digitalgemology.com/learn/diamond-anatomy/parts-of-a-diamond","https://digitalgemology.com/learn/diamond-anatomy/diamond-measurements-explained","https://digitalgemology.com/learn/diamond-anatomy/diamond-table-percentage","https://digitalgemology.com/learn/diamond-anatomy/diamond-crown-angle","https://digitalgemology.com/learn/diamond-anatomy/diamond-pavilion-angle","https://digitalgemology.com/learn/diamond-anatomy/star-length-and-lower-half-length","https://digitalgemology.com/learn/diamond-anatomy/diamond-girdle-thickness","https://digitalgemology.com/learn/diamond-anatomy/diamond-culet","https://digitalgemology.com/learn/diamond-anatomy/how-to-read-diamond-proportions"]},{"title":"How to read a diamond grading report","course":"Reading a grading report","url":"https://digitalgemology.com/learn/grading-reports","lessons":["https://digitalgemology.com/learn/grading-reports/what-is-a-diamond-grading-report","https://digitalgemology.com/learn/grading-reports/diamond-report-identity-section","https://digitalgemology.com/learn/grading-reports/diamond-report-grades","https://digitalgemology.com/learn/grading-reports/what-ideal-cut-means","https://digitalgemology.com/learn/grading-reports/polish-symmetry-and-fluorescence","https://digitalgemology.com/learn/grading-reports/diamond-clarity-plot","https://digitalgemology.com/learn/grading-reports/diamond-proportion-diagram","https://digitalgemology.com/learn/grading-reports/diamond-report-comments-treatments-origin","https://digitalgemology.com/learn/grading-reports/how-to-read-a-diamond-grading-report"]},{"title":"Diamond vs moissanite","course":"Diamond vs moissanite","url":"https://digitalgemology.com/learn/diamond-vs-moissanite","lessons":["https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-differences","https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-vs-moissanite-properties","https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-refractive-index-and-cut","https://digitalgemology.com/learn/diamond-vs-moissanite/why-moissanite-has-more-fire","https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-doubled-facets-loupe-test","https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-carat-size","https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-color-and-fluorescence","https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite","https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-certificate-vs-diamond-report","https://digitalgemology.com/learn/diamond-vs-moissanite/moissanite-vs-diamond-durability-and-care"]},{"title":"Historic diamond cuts: the history of the brilliant","course":"The history of the brilliant","url":"https://digitalgemology.com/learn/historic-cuts","lessons":["https://digitalgemology.com/learn/historic-cuts/old-single-cut-diamond","https://digitalgemology.com/learn/historic-cuts/mazarin-cut-diamond","https://digitalgemology.com/learn/historic-cuts/peruzzi-cut-diamond","https://digitalgemology.com/learn/historic-cuts/old-mine-cut-diamond","https://digitalgemology.com/learn/historic-cuts/old-european-cut-diamond","https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919","https://digitalgemology.com/learn/historic-cuts/hearts-and-arrows-diamonds","https://digitalgemology.com/learn/historic-cuts/beyond-the-tolkowsky-brilliant"]},{"title":"The bow-tie effect","course":"The bow-tie files","url":"https://digitalgemology.com/learn/bow-tie","lessons":["https://digitalgemology.com/learn/bow-tie/bow-tie-effect-in-diamonds","https://digitalgemology.com/learn/bow-tie/which-diamond-shapes-have-a-bow-tie","https://digitalgemology.com/learn/bow-tie/bow-tie-tilt-and-head-shadow","https://digitalgemology.com/learn/bow-tie/what-causes-a-bow-tie","https://digitalgemology.com/learn/bow-tie/is-a-bow-tie-always-present","https://digitalgemology.com/learn/bow-tie/bow-tie-and-the-grading-report","https://digitalgemology.com/learn/bow-tie/why-cutters-leave-a-bow-tie","https://digitalgemology.com/learn/bow-tie/how-to-fix-a-bow-tie","https://digitalgemology.com/learn/bow-tie/how-to-check-a-diamond-for-a-bow-tie"]}]}