T73 Round Brilliant GGG: more facets, more sparkle
Brilliance 98 · Fire 76 · Scintillation 80 · in our census, where the T57 scores 98 · 77 · 72 in GGG
How the T73 Round Brilliant handles light in GGG, measured: brilliance 98, fire 76 and 2% 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 GGG, face-up, from our own tracer at refractive index 1.97. Red, green and blue return light to the eye; gray leaks.
T73 Round Brilliant GGG
GGG has a refractive index of 1.970 and a dispersion of 0.045. Its critical angle, from the low end of that range, is 30.5°, so a round design needs a pavilion of at least 37.4° for head-on light to reflect off both sides of the pavilion and leave through the table. We trace it with one index, 1.970, the midpoint of the published range, and a fire spread of 0.039, 0.86 of the published dispersion. Every picture here is our Light Return tracer at 1.970, and every figure is from the same light census that scores the other gemstones; the 3D Gemstone Simulator shows the T73 Round Brilliant in GGG 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 GGG, the census returns 98 of 100 for brilliance and 76 for fire, against 98 and 77 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 GGG 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 GGG (white) against the T57 Round Brilliant in GGG (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 ggg: ahead on 3, level on 3, behind on 2.
Global90, the comparison 89, difference +1
Brilliance98, the comparison 98, difference 0
Fire76, the comparison 77, difference −1
Scintillation80, the comparison 72, difference +8
Spread100, the comparison 101, difference −1
Symmetry100, the comparison 100, difference 0
Shape-norm105, the comparison 105, difference 0
Tilt82, the comparison 81, difference +1
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 GGG
More facets, more sparkle
Scintillation 80 against 72 for the T57 Round Brilliant in GGG: 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.
Brilliance 98 against 93 for the T73 Round Brilliant in diamond: 5 points higher
The same cut in diamond returns 93. GGG bends light less than diamond: its critical angle is 30.5°, 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 more of GGG's light than of diamond's, as the two maps show.
T73 Round Brilliant in GGG · Brilliance 98
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.
2.02 ct at 6.5 mm, against 1.01 ct for the same cut in diamond (+100%)
Weight follows specific gravity: 7.05 for GGG against 3.52 for diamond, so the same model at the same size weighs 2.02 ct here and 1.01 ct in diamond, 6.5 mm across. Nothing about the light changes with it.
A T73 Round Brilliant 6.5 mm across, weighed from the model's measured volume and each stone's specific gravity.
Tilt 82 against 92 for the T73 Round Brilliant in diamond: 10 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 82 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 GGG · Tilt 82
0° · 0% leak
10° · 4% leak
20° · 14% leak
30° · 23% 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-M5 reads 98 for tilt in GGG, the best of the cuts we score there.
Face-up size 100 against 107 for the T57 Round Brilliant in GGG (T73 = 100): 7% less face-up area for the same weight
Face-up size is the outline's area per carat, measured from each model (T73 = 100): 100 for the T73 Round Brilliant against 107 for the T57. The same volume spread over a longer or shallower outline shows more face for the weight; it is the same in every stone, because specific gravity scales every cut alike.
T73 Round Brilliant · 5.14 mm at 1.00 ct · Face-up size 100
T57 Round Brilliant · 5.31 mm at 1.00 ct · Face-up size 107
Both stones weigh 1.00 ct in GGG and are drawn to the same scale in millimeters, from each cut's own model. Face-up size is the outline's area per carat, with the T73 at 100: a deeper stone, or a rounder outline, spreads less area for its weight.
What helps:the Marquise Cut reads 121 for face-up size in GGG, the best of the cuts we score there.
Pick the T73 Round Brilliant in GGG for this: it has more facets to sparkle with and returns more light than in diamond. The catch: it weighs more than in diamond, loses more light when tilted than in diamond and faces up smaller for its weight.
If that catch matters more to you, the DG-M5 reads 98 for tilt in GGG, 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 GGG: questions
Is the T73 a good cut for GGG?
In our census the T73 Round Brilliant returns 98 of 100 for brilliance and 76 for fire in GGG, against 98 and 77 for the T57 in the same stone. Against that round and against the same cut in diamond it has 2 pros and 3 cons by our thresholds; the summary above names them.
What pavilion angle does GGG need?
At least 37.4° for a round design: GGG's critical angle is 30.5°, 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 GGG?
At 6.5 mm across, 2.02 ct in GGG, against 1.01 ct for the same cut in diamond (+100%): GGG's specific gravity is 7.05, diamond's 3.52.
Can I see the T73 in GGG in 3D?
Yes: the 3D Gemstone Simulator renders it live, with GGG's own refractive index and dispersion. GGG 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).
