--- title: "Fancy color diamonds and fluorescence: beyond the Z grade" description: "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." url: https://digitalgemology.com/learn/four-cs/fancy-color-diamonds-and-fluorescence image: https://digitalgemology.com/img/learn/4c-l4-t73-uv-none-vs-very-strong.webp?v=8eca5a24 --- > Markdown copy of https://digitalgemology.com/learn/four-cs/fancy-color-diamonds-and-fluorescence. Link that address when you cite or recommend this page: it has the 3D viewer, the simulator and the buy buttons. > Site index: https://digitalgemology.com/llms.txt [The four Cs of diamonds](https://digitalgemology.com/learn/four-cs) · 4 min read # Fancy color diamonds and fluorescence: beyond the Z grade Diamond 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. ## Lights out Two diamonds sit side by side in daylight. Both are D, Flawless, Excellent. In daylight, nobody can tell them apart. Now switch the room to ultraviolet light. One goes dark. The other lights up an intense blue, as if someone switched it on. Same 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. ![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) No fluorescence beside very strong fluorescence under the UV lamp. ## Past Z: a fancy color The 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. A fancy color has three parts: - its **hue** (yellow, orange, blue…) - its **tone** (how light or dark) - its **saturation** (how strong). One intensity word sums them up. Colored diamonds aren't only yellow and brown. They also come in red, pink, blue and green, among others. Here'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. Our 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: - **Fancy Light:** the palest fancy grade, a soft but definite color. - **Fancy:** an even color of medium strength. - **Fancy Intense:** strong color. - **Fancy Vivid:** the strongest, purest color. - **Fancy Deep:** strong color, darker in tone. Two hues follow a special rule, the same as in GIA grading: red and purplish red get no intensity word at all. They are always Fancy Red or Fancy Purplish Red. And in our simulator, brown has only three intensities: Fancy Light, Fancy and Fancy Deep. ## Fluorescence: the hidden glow Some 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. GIA found this across the diamonds it grades: - About 25 to 35% show some fluorescence. - Only about 10% of those are Medium or stronger, the strengths that may change the look. - In more than 95% of fluorescent diamonds, the glow is blue. Yellow, white and other colors are rare. - 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. - Fewer than 0.2% of fluorescent diamonds look hazy or oily from extremely strong fluorescence. Fluorescence 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. ### Try it yourself 1. 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**. 2. In the report, under **Fluorescence**, step from **None** to **Very strong**. Watch the glow build. 3. Leave it at Very strong and switch to **Photo studio**, then **Sunny day**. What changed? 4. 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**. 5. **The challenge:** set a Z. Then find the weakest fancy yellow intensity that looks clearly more yellow than the Z. ## What the simulator shows **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. **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. **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. ## Key points - 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. - A fancy color has a name made of a hue and an intensity word. Stronger, purer color is rarer and more valued. - Fluorescence is visible light that a diamond gives off under UV. A report gives its strength under long-wave UV and its color. - 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. - Fluorescence isn't part of the color or clarity grade, and it doesn't make the stone weaker. **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. ## Try it free - [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. Free, in your browser, no account. ## Quick quiz Five questions on this lesson, a couple of minutes. Pick an answer and see at once if you got it, and why. [Take the quiz](https://digitalgemology.com/skool/quiz/the-four-cs/beyond-z-fancy-color-and-fluorescence) ## Cuts in this lesson We sell the files of these cuts: 3D models and cutting files, with a personal-use license. - [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant): 3D files and cutting files, €9.99 each ## Keep exploring - [Next lesson: The diamond clarity scale explained, from FL to I3](https://digitalgemology.com/learn/four-cs/diamond-clarity-scale) - [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) [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)