T73 Round Brilliant Amethyst: Pros & Cons

On every other amethyst page the T73 is the yardstick. Here it is set against the T57, the 1919 plan it adds sixteen girdle facets to, and against the same cut in diamond.

The T73 we measure is 61.7% deep, with 73 facets over a 40.75° pavilion. That pavilion clears amethyst's guide minimum of 40.4° by under half a degree.

Against the T57 it differs only where a girdle band can make a difference, in sparkle: Brilliance 72 against 71, Fire 36 against 37, Tilt level too. Against diamond the gaps are large, and they are what quartz does to any round.

Is a round brilliant good for amethyst? Pros and cons

Pros

A quarter lighter than diamond 0.76 vs 1.01 ct
More sparkle than the T57 80 vs 72

Cons

Less than half the diamond's fire 36 vs 78
Far more leakage than in diamond 28 vs 2
Less light than in diamond 72 vs 93
Keeps less light when tipped 80 vs 92

Compared with the T57 Round Brilliant in amethyst and with the T73 Round Brilliant in diamond. A difference counts from 3 points (Brilliance, Fire, Tilt, Leakage), 5 (Scintillation, Symmetry), 2 (Spread) or 5% (weight); Tilt counts as a pro only for a stone within 5 points of the brilliance it is compared with. How we measure.

All eight scores against the T57

At a glance: the T73 Round Brilliant in amethyst (white) against the T57 Round Brilliant in amethyst (dashed): solid white where it reaches further, hatched where it falls short. Each pro and con is explained, with pictures, below.

Against the T57 Round Brilliant in amethyst: ahead on 4, level on 2, behind on 2.

Global70, the comparison 69, difference +1
Brilliance72, the comparison 71, difference +1
Fire36, the comparison 37, difference −1
Scintillation80, the comparison 72, difference +8
Spread100, the comparison 101, difference −1
Symmetry100, the comparison 100, difference 0
Shape-norm77, the comparison 77, difference 0
Tilt80, the comparison 79, difference +1

Face-up light census, a different measure from the Cut Grading Tool; Spread and Shape-norm above 100 sit on the ring.

Open it in the Cut Performance Wheel

What amethyst gains in a T73

A quarter lighter than diamond

0.76 ct at 6.5 mm, against 1.01 ct for the same cut in diamond (−25%)

Quartz is the light material here: a T73 6.5 mm across is 0.76 ct in amethyst and 1.01 ct in diamond.

A T73 Round Brilliant 6.5 mm across, weighed from the model's measured volume and each stone's specific gravity.

Try it yourself: Weights in all seven gemstones on the T73 Round Brilliant page

More sparkle than the T57

Scintillation 80 against 72 for the T57 Round Brilliant in amethyst: 8 points higher

The sixteen girdle facets are what our scintillation score sees: 73 facets against the T57's 57.

T73 Round Brilliant · 73 facets · Scintillation 80

T57 Round Brilliant · 57 facets · Scintillation 72

Scintillation follows the number of facets: more facets, more and smaller flashes as the stone moves. Count the facets in each crown. Drawn from each cut's own model.

Try it yourself: Compare the Scintillation spoke in the Cut Performance Wheel

What quartz costs the T73

Less than half the diamond's fire

Fire 36 against 78 for the T73 Round Brilliant in diamond: 42 points lower

The cause is the stone. Amethyst's dispersion of 0.013 is under a third of diamond's 0.044, and the same crown cannot split out colour that is not there.

T73 round brilliant in amethyst face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 36) — Look at the coloured flashes: those are fire. Same light, same size, same face-up angle; rendered by our 3D Gemstone Simulator from each cut's own model.

T73 round brilliant in diamond face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 78) — Look at the coloured flashes: those are fire. Same light, same size, same face-up angle; rendered by our 3D Gemstone Simulator from each cut's own model.

What helps: DG-Anteros Amethyst keeps the same plan and reaches 54 in amethyst; the Oval Cut Amethyst 69.

Try it yourself: See the fire in the 3D Gemstone Simulator

Far more leakage than in diamond

Leakage 28 against 2 for the T73 Round Brilliant in diamond: 26 points higher

In diamond the T73 lets almost nothing out of the back, and its tilt strip stays largely clear at every angle. Quartz's critical angle of about 40.4° gives light many more ways through the pavilion.

T73 round brilliant in amethyst tilted 0 degrees: Light Return map, 13% of the face leaking — Each frame is the Light Return map with the stone tilted away from you by the angle shown; grey is light leaving through the pavilion. The share under each frame is that picture's own.

T73 round brilliant in amethyst tilted 10 degrees: Light Return map, 38% of the face leaking — Each frame is the Light Return map with the stone tilted away from you by the angle shown; grey is light leaving through the pavilion. The share under each frame is that picture's own.

What helps: Not a steeper pavilion: 40.75° is already above the guide minimum. DG-M5 Amethyst leaks 15% in amethyst, DG-Anteros Amethyst 18%.

Try it yourself: Tilt it yourself in the simulator's light map

Less light than in diamond

Brilliance 72 against 93 for the T73 Round Brilliant in diamond: 21 points lower

The T73's proportions were worked out for diamond, not quartz. In amethyst they still return more light than most cuts we measure, about a quarter less than the diamond version.

T73 round brilliant in amethyst face-up Light Return map: red, green and blue show where the light returns from, grey shows where it leaks (Brilliance 72) — Red, green and blue = light returning to the eye; grey = light leaving through the pavilion. This is the head-on view; the Brilliance score averages a wider cone of light, so the score can differ from what one picture shows.

T73 round brilliant in diamond face-up Light Return map: red, green and blue show where the light returns from, grey shows where it leaks (Brilliance 93) — Red, green and blue = light returning to the eye; grey = light leaving through the pavilion. This is the head-on view; the Brilliance score averages a wider cone of light, so the score can differ from what one picture shows.

What helps: In amethyst, DG-M5 Amethyst returns 85 and DG-Anteros Amethyst 82.

Try it yourself: Open this Light Return map in the simulator

Keeps less light when tipped

Tilt 80 against 92 for the T73 Round Brilliant in diamond: 12 points lower

Tipped by 20°, the T73 keeps 80 of its face-up light in amethyst, against 92 in diamond.

What helps: The T105 Round Brilliant Amethyst keeps 87 when tipped, but returns less light face-up, 65.

Try it yourself: Compare the Tilt spoke in the Cut Performance Wheel

Who a T73 round amethyst suits

The T73 is the safe round for amethyst: published proportions, a girdle a setter can seat, and the third-highest brilliance we measure in this stone.

Many hobby cutters learn on amethyst, and the standard round is usually the first plan they cut. A deep, evenly coloured stone also hides the colour zoning quartz rough often carries, which a round's many facets help to blend.

For more light on the same 73-facet plan, DG-Anteros Amethyst; for the most, DG-M5 Amethyst.

T73 Round Brilliant Amethyst: questions

Is a round brilliant a good cut for amethyst?

A solid one: Brilliance 72 in our census, behind only DG-M5 (85) and DG-Anteros (82) of the cuts we measure in amethyst.

T73 or T57 for amethyst?

The T73 sparkles more, 80 against 72, and has a girdle to seat. Light and fire are level.

How much fire does a round amethyst have?

Fire 36 in our census, against 78 for the same cut in diamond.

What does a 6.5 mm round amethyst weigh?

About 0.76 ct in the T73; a diamond of that width is 1.01 ct.

Get the T73 Round Brilliant Cut files

6 formatsMillimetresWatertight

T73 Round Brilliant Cut 3D files

The T73 Round Brilliant Cut as exact geometry: 73 planar facets, real-world scale, ready for CAD, rendering, printing and casting.

STEPExact faceted solid for CAD
3DMRhino, closed mesh on its own layer
STLWatertight mesh for printing and casting
OBJMesh for modelling and rendering
FBXBlender, 3ds Max, Maya, Cinema 4D, Unity, Unreal
GLBWeb, AR and quick previews

€9.99 · Personal useBuy the 3D files

GemCad96 index

T73 Round Brilliant Cut cutting files

The T73 Round Brilliant Cut as a faceting design: 57 + 16 girdles = 73 facets, 96 index, 8-fold mirror-image symmetry, ready for the machine.

.ascGemCad design file, 96 index gear
.csvTier table: angles, indices and cutting order
DiagramPrintable faceting diagram

€9.99 · Personal useBuy the cutting files

Questions before you buy? Email us.

More gemstones and cuts

Amethyst: optical properties and the top ten cuts · The T73 Round Brilliant: specifications, model and files

T73 Round Brilliant Amethyst: the modern round, with more sparkle than the T57