T57 Round Brilliant Amethyst: Pros & Cons

The T57 is the round brilliant with nothing added: table, eight stars, eight bezels, sixteen upper halves, eight pavilion mains and sixteen lower halves, meeting at a knife-edge girdle. It follows the proportions published in Diamond Design in 1919. In the model we trace, the mains fall at 40.75° and the knife-edge stone stands 59.2% of its width deep.

In amethyst it tracks the T73 closely: Brilliance 71 against 72, Fire 37 against 36, leakage 29% against 28%. It sparkles less than the T73 (72 against 80); that gap is real, and it is missing from the cons only because each page lists four at most.

Is the T57 a good cut for amethyst? Pros and cons

Pros

Lighter than diamond 0.69 vs 0.92 ct

Cons

Less than half the diamond's fire 37 vs 79
Over a quarter of the light leaks 29 vs 2
Less light than the diamond version 71 vs 92
Keeps less light when tipped 79 vs 90

Compared with the T73 Round Brilliant in amethyst and with the T57 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 T73

At a glance: the T57 Round Brilliant in amethyst (white) against the T73 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 T73 Round Brilliant in amethyst: ahead on 2, level on 2, behind on 4.

Global69, the comparison 70, difference −1
Brilliance71, the comparison 72, difference −1
Fire37, the comparison 36, difference +1
Scintillation72, the comparison 80, difference −8
Spread101, the comparison 100, difference +1
Symmetry100, the comparison 100, difference 0
Shape-norm77, the comparison 77, difference 0
Tilt79, the comparison 80, 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 T57

Lighter than diamond

0.69 ct at 6.5 mm, against 0.92 ct for the same cut in diamond (−25%)

At 6.5 mm the T57 comes to 0.69 ct in amethyst; the same knife-edge round in diamond is 0.92 ct.

A T57 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 T57 Round Brilliant page

What quartz costs the T57

Less than half the diamond's fire

Fire 37 against 79 for the T57 Round Brilliant in diamond: 42 points lower

The 1919 angles split light well in diamond. Quartz, dispersing under a third as strongly, cannot follow.

T57 round brilliant in amethyst face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 37) — 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.

T57 round brilliant in diamond face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 79) — 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: Among rounds in amethyst, DG-Anteros Amethyst reaches 54; the Oval Cut Amethyst 69.

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

Over a quarter of the light leaks

Leakage 29 against 2 for the T57 Round Brilliant in diamond: 27 points higher

29% of the light in our census passes out through the pavilion in amethyst. With diamond's critical angle of 24.4° the same pavilion holds almost everything; with quartz's 40.4° it cannot.

T57 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.

T57 round brilliant in amethyst tilted 10 degrees: Light Return map, 39% 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: The pavilion already sits at 40.75°, above amethyst's guide minimum of 40.4°, so a steeper one is not what our data points to. DG-M5 Amethyst leaks 15%.

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

Less light than the diamond version

Brilliance 71 against 92 for the T57 Round Brilliant in diamond: 21 points lower

In diamond this cut returns 92. In amethyst it returns about what the T73 does, which still puts it among the five brightest cuts we measure in quartz.

T57 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 71) — 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.

T57 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 92) — 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: DG-M5 Amethyst returns 85, DG-Anteros Amethyst 82.

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

Keeps less light when tipped

Tilt 79 against 90 for the T57 Round Brilliant in diamond: 11 points lower

Tipped by 20°, it keeps 79 of its face-up light in amethyst against 90 in diamond: a smaller loss than on light or fire, but past our threshold.

What helps: Within the same family, the T105 Round Brilliant Amethyst keeps 87 when tipped, at a lower 65 brilliance.

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

Who a T57 amethyst suits

Choose the T57 in amethyst for period work, for teaching, or to show the brilliant as it was first published. It gives up almost nothing in light to the T73.

Its knife-edge girdle is the practical catch: quartz, at 7 on the Mohs scale, chips there far more easily than diamond.

For a girdle a setter can seat and more sparkle, the T73 Round Brilliant Amethyst. For more light, DG-M5 Amethyst.

T57 Round Brilliant Amethyst: questions

Is the T57 good for amethyst?

As good as the T73 for light: Brilliance 71 against 72, with 29% leakage against 28%.

T57 or T73 round for amethyst?

The T73 sparkles more (80 against 72) and has a faceted girdle; light and fire are level.

Does a T57 amethyst have fire?

Fire 37 in our census, about the T73's 36 and well under 79 for the same cut in diamond.

Get the T57 Round Brilliant Cut files

6 formatsMillimetresWatertight

T57 Round Brilliant Cut 3D files

The T57 Round Brilliant Cut as exact geometry: 57 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

T57 Round Brilliant Cut cutting files

The T57 Round Brilliant Cut as a faceting design: 57 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 T57 Round Brilliant: specifications, model and files

T57 Round Brilliant Amethyst: the 1919 round, a quarter lighter in weight than diamond