T105 Round Brilliant Amethyst: Pros & Cons

The T105 adds eight crown star halves and splits the T57's lower halves into three rows, with no girdle band: crown and pavilion meet at a knife edge. Our model has 105 facets, a 40.75° main pavilion and a depth of 59.3%.

In diamond it edges past the T73 for light. In amethyst it returns less and leaks more. The added facets are cut a little steeper than the mains, and our census measures the result rather than the reason.

It holds its light well when tipped, 87 against 80 for the T73, but from a smaller start, so we do not count that as a pro.

Is the T105 a good round for amethyst? Pros and cons

Pros

Lighter than diamond 0.69 vs 0.92 ct
More sparkle than the T73 90 vs 80

Compared with the T73 Round Brilliant in amethyst and with the T105 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 T105 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 3, level on 1, behind on 4.

Global68, the comparison 70, difference −2
Brilliance65, the comparison 72, difference −7
Fire31, the comparison 36, difference −5
Scintillation90, the comparison 80, difference +10
Spread101, the comparison 100, difference +1
Symmetry100, the comparison 100, difference 0
Shape-norm70, the comparison 77, difference −7
Tilt87, the comparison 80, difference +7

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 T105

Lighter than diamond

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

Knife-edged and 59.3% deep, a 6.5 mm T105 weighs 0.69 ct in amethyst against 0.92 ct in diamond.

A T105 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 T105 Round Brilliant page

More sparkle than the T73

Scintillation 90 against 80 for the T73 Round Brilliant in amethyst: 10 points higher

Three rows of lower halves and the extra star halves divide the face into more, smaller facets, and our facet-based scintillation score climbs with them.

T105 Round Brilliant · 105 facets · Scintillation 90

T73 Round Brilliant · 73 facets · Scintillation 80

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

The catch with a T105 amethyst

Much less fire than in diamond

Fire 31 against 77 for the T105 Round Brilliant in diamond: 46 points lower

Amethyst splits light into colour far more weakly than diamond, and the T105's finer facets make each flash smaller still.

T105 round brilliant in amethyst face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 31) — 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.

T105 round brilliant in diamond face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 77) — 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: The Oval Cut Amethyst scores 69 for fire in amethyst; among rounds, DG-Anteros Amethyst scores 54.

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

A third of the light leaks

Leakage 35 against 1 for the T105 Round Brilliant in diamond: 34 points higher

35% of the light leaves through the pavilion in our census. In diamond the same cut loses almost none; in amethyst it loses more than the T73's 28%.

T105 round brilliant in amethyst tilted 0 degrees: Light Return map, 22% 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.

T105 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: The main pavilion is at 40.75°, above the 40.4° guide minimum, so steepening it is not the fix. The T73 Round Brilliant Amethyst leaks 28%, DG-M5 Amethyst 15%.

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

Far less light than in diamond

Brilliance 65 against 95 for the T105 Round Brilliant in diamond: 30 points lower

Moved from diamond to quartz, the T105 drops further than the T73 does, and ends below it.

T105 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 65) — 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.

T105 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 95) — 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: For a round with more light in amethyst, the T73 Round Brilliant Amethyst (72) or DG-M5 Amethyst (85).

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

Who a T105 amethyst suits

Choose the T105 in amethyst for sparkle and for a stone that changes little as it tips, accepting a face that returns less light than the T73.

Its knife-edge girdle needs a setting that protects it, and quartz at hardness 7 chips far more readily than diamond at 10.

For a girdle a setter can seat and more light, the T73 Round Brilliant Amethyst. For the finest sparkle with the T73's light, DG-Vitruvio Amethyst.

T105 Round Brilliant Amethyst: questions

Is the T105 a good cut for amethyst?

For sparkle, yes: 90 against 80. For light, the T73 does better: 72 against 65.

Why does the T105 lose light in amethyst but not in diamond?

Our census shows that it does: 35% leaks in amethyst, 1% in diamond. Quartz's critical angle of about 40.4° is far larger than diamond's, and the added pavilion facets meet it differently.

Does a T105 amethyst hold its light when tilted?

Well: Tilt 87, against 80 for the T73. It keeps a steady share of a smaller amount.

What does a 6.5 mm T105 amethyst weigh?

0.69 ct, against 0.92 ct in diamond.

Get the T105 Round Brilliant Cut files

6 formatsMillimetresWatertight

T105 Round Brilliant Cut 3D files

The T105 Round Brilliant Cut as exact geometry: 105 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

T105 Round Brilliant Cut cutting files

The T105 Round Brilliant Cut as a faceting design: 105 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 T105 Round Brilliant: specifications, model and files

T105 Round Brilliant Amethyst: more sparkle than the T73, at a cost in light