T73 Round Brilliant Topaz: more facets, more sparkle
Brilliance 86 · Fire 35 · Scintillation 80 · in our census, where the T57 scores 85 · 36 · 72 in topaz
How the T73 Round Brilliant handles light in topaz, measured: brilliance 86, fire 35 and 14% leakage, set against the T57 in the same stone and against the same cut in diamond.
Light Return map of the T73 Round Brilliant in topaz, face-up, from our own tracer at refractive index 1.606. Red, green and blue return light to the eye; gray leaks.
T73 Round Brilliant Topaz
Topaz has a refractive index of 1.606 to 1.644 and a dispersion of 0.014. Its critical angle, from the low end of that range, is 38.5°, so a round design needs a pavilion of at least 38.5° for head-on light to reflect off both sides of the pavilion and leave through the table. We trace it with one index, 1.625, the midpoint of the published range, and a fire spread of 0.012, 0.86 of the published dispersion. Every picture here is our Light Return tracer at 1.606, and every figure is from the same light census that scores the other gemstones; the 3D Gemstone Simulator shows the T73 Round Brilliant in topaz live.
The T73 Round Brilliant has 73 facets and a total depth of 61.7% of its width; its pavilion mains sit at 40.8°. In topaz, the census returns 86 of 100 for brilliance and 35 for fire, against 85 and 36 for the T57, our benchmark, in the same stone; the same T73 Round Brilliant in diamond reads 93 and 78.
Compared with the T57 Round Brilliant in topaz and with the T73 Round Brilliant in diamond.
A difference counts from 3 points (Brilliance, Fire, Tilt, Leakage), 5 (Scintillation,
Symmetry), 4% (face-up size per carat) 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 topaz (white) against the T57 Round Brilliant in topaz (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 topaz: ahead on 3, level on 3, behind on 2.
Global75, the comparison 74, difference +1
Brilliance86, the comparison 85, difference +1
Fire35, the comparison 36, difference −1
Scintillation80, the comparison 72, difference +8
Spread100, the comparison 101, difference −1
Symmetry100, the comparison 100, difference 0
Shape-norm92, the comparison 92, difference 0
Tilt74, the comparison 74, difference 0
Face-up light census, a different measure from the Cut Grading Tool; Spread and Shape-norm above 100 sit on the ring. Spread is the census's estimate from depth alone; the face-up size in the pros and cons is measured from each model's outline. Open it in the Cut Performance Wheel; these are the same census figures as our Cut Performance Index.
What the T73 Round Brilliant gains in topaz
More facets, more sparkle
Scintillation 80 against 72 for the T57 Round Brilliant in topaz: 8 points higher
Scintillation follows the number of facets the stone shows: 100 × (1 − e^(−facets / 45)). The T73 Round Brilliant has 73 facets and the T57 57, so 80 against 72. It depends on the geometry alone, so it is the same in every stone.
Scintillation follows the number of facets: more facets, more and smaller flashes as the stone moves. Compare the facet counts under the drawings; each drawing shows only the crown. Drawn from each cut's own model.
Fire 35 against 78 for the T73 Round Brilliant in diamond: 43 points lower
Fire is the share of the returned light that splits into color at the exit facet: the census traces each exit again at the refractive index minus and plus the fire spread (0.012 in topaz) and counts a ray as fire when the two directions differ by more than 0.6°. The T73 Round Brilliant reads 35 against 78 for the same cut in diamond. The figure is the census's; the 3D Gemstone Simulator renders topaz's fire live.
The fire figure is the census's, traced at the refractive index minus and plus the fire spread. See the fire in the 3D Gemstone Simulator: the T73 Round Brilliant in topaz under the sunny-day lighting.
What helps:the Oval Cut reads 68 for fire in topaz, the best of the cuts we score there.
Tilt 74 against 92 for the T73 Round Brilliant in diamond: 18 points lower
Tilt is how much of its face-up brilliance a stone keeps when the census tilts it 20° about its long axis, with 2,200 rays. The T73 Round Brilliant keeps 74 against 92 for the same cut in diamond. The tilt strips below show the maps at 0°, 10°, 20° and 30°, with each picture's own leak share under it.
T73 Round Brilliant in topaz · Tilt 74
0° · 10% leak
10° · 28% leak
20° · 32% leak
30° · 37% leak
T73 Round Brilliant in diamond · Tilt 92
0° · 4% leak
10° · 2% leak
20° · 9% leak
30° · 14% leak
Tilt is how much of its own face-up light a stone keeps when tilted. Each frame is the Light Return map with the stone tilted away from you by the angle shown; gray is leakage. The share under each frame is that picture's own.
What helps:the DG-Miliano reads 86 for tilt in topaz, the best of the cuts we score there.
Leakage 14 against 2 for the T73 Round Brilliant in diamond: 12 points higher
Leakage is the share of the census rays that enter the stone and leave through the pavilion, or through the crown heading down. The T73 Round Brilliant leaks 14% in topaz against 2% for the same cut in diamond. Grey in the maps below is leaking light; the share under each picture is that picture's own.
T73 Round Brilliant in topaz · Leakage 14
0° · 10% leak
10° · 28% leak
20° · 32% leak
30° · 37% leak
T73 Round Brilliant in diamond · Leakage 2
0° · 4% leak
10° · 2% leak
20° · 9% leak
30° · 14% leak
Each frame is the Light Return map with the stone tilted away from you by the angle shown; gray is leakage. The share under each frame is that picture's own.
What helps:the DG-M5 reads 4% for leakage in topaz, the best of the cuts we score there.
Brilliance 86 against 93 for the T73 Round Brilliant in diamond: 7 points lower
The same cut in diamond returns 93. Topaz bends light less than diamond: its critical angle is 38.5°, diamond's 24.4°, so a pavilion facet has to be steeper before light reflects off it rather than passing out. The T73 Round Brilliant's pavilion returns less of topaz's light than of diamond's, as the two maps show.
T73 Round Brilliant in topaz · Brilliance 86
T73 Round Brilliant in diamond · Brilliance 93
Red, green and blue = light returning to the eye; gray = leakage, light that leaves heading down or stays inside. 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:the DG-M5 reads 96 for brilliance in topaz, the best of the cuts we score there.
Pick the T73 Round Brilliant in topaz for this: it has more facets to sparkle with. The catch: it shows less fire than in diamond, loses more light when tilted than in diamond, leaks more than in diamond and returns less light than in diamond.
If that catch matters more to you, the Oval Cut reads 68 for fire in topaz, the best of the cuts we score there.
Every figure on this page is from our light census, traced at one refractive index: a simulation of the geometry, not a grading report. The 3D files and cutting files below are the same T73 Round Brilliant model we traced.
T73 Round Brilliant Topaz: questions
Is the T73 a good cut for topaz?
In our census the T73 Round Brilliant returns 86 of 100 for brilliance and 35 for fire in topaz, against 85 and 36 for the T57 in the same stone. Against that round and against the same cut in diamond it has 1 pro and 4 cons by our thresholds; the summary above names them.
What pavilion angle does topaz need?
At least 38.5° for a round design: topaz's critical angle is 38.5°, from the low end of its refractive index range, and head-on light has to reflect off both sides of the pavilion and leave through the table. The T73 Round Brilliant's pavilion mains sit at 40.8°.
How much does a T73 weigh in topaz?
At 6.5 mm across, 1.01 ct in topaz, against 1.01 ct for the same cut in diamond, the same weight to the per cent: topaz's specific gravity is 3.535, diamond's 3.52.
Can I see the T73 in topaz in 3D?
Yes: the 3D Gemstone Simulator renders it live, with topaz's own refractive index and dispersion. Topaz is traced by the same light census as the other gemstones, with its refractive index and fire spread derived from published values, so its scores are on the same scale; the pictures here are our Light Return tracer, and the Cut Performance Wheel sets it against any other cut and stone.
Get the T73 Round Brilliant Cut files
6 formatsMillimetersWatertight
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.
Save with a bundle: the T73 Round Brilliant Cut 3D files are also in Jewelry Essentials 3D, 10 cuts for €29.99 until 1 December, then €39.99 (€99.90 as single files). Buy the bundle.
Not sure the files open in your software? Get the cube free: the same six formats, for your email address, used only to send them (privacy).
