Brilliance 55 · Fire 89 · Scintillation 44 · in our census, where the T73 scores 98 · 76 · 80 in GGG
How the Old Single Cut handles light in GGG, measured: brilliance 55, fire 89 and 36% leakage, set against the T73 in the same stone and against the same cut in diamond.
Light Return map of the Old Single Cut in GGG, face-up, from our own tracer at refractive index 1.97. Red, green and blue return light to the eye; gray leaks.
Old Single Cut 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 Old Single Cut in GGG live.
The Old Single Cut has 26 facets, a table of 57.5% of its width and a total depth of 67.5% of its width; its pavilion mains sit at 48.5°. In GGG, the census returns 55 of 100 for brilliance and 89 for fire, against 98 and 76 for the T73, our benchmark, in the same stone; the same Old Single Cut in diamond reads 72 and 84.
Is GGG good in an Old Single? Pros and cons, measured
Compared with the T73 Round Brilliant in GGG and with the Old Single Cut 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 T73
At a glance: the Old Single Cut in GGG (white) against the T73 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 T73 Round Brilliant in ggg: ahead on 2, level on 1, behind on 5.
Global73, the comparison 90, difference −17
Brilliance55, the comparison 98, difference −43
Fire89, the comparison 76, difference +13
Scintillation44, the comparison 80, difference −36
Spread97, the comparison 100, difference −3
Symmetry100, the comparison 100, difference 0
Shape-norm59, the comparison 105, difference −46
Tilt100, the comparison 82, difference +18
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 Old Single Cut gains in GGG
More fire than the T73 in GGG
Fire 89 against 76 for the T73 Round Brilliant in GGG: 13 points higher
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 (0.039 in GGG) and counts a ray as fire when the two directions differ by more than 0.6°. The Old Single Cut reads 89 against 76 for the T73 in GGG. The figure is the census's; the 3D Gemstone Simulator renders GGG'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 Old Single Cut in GGG under the sunny-day lighting.
2.11 ct at 6.5 mm, against 1.05 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 2.11 ct here and 1.05 ct in diamond, 6.5 mm across. Nothing about the light changes with it.
A Old Single Cut 6.5 mm across, weighed from the model's measured volume and each stone's specific gravity.
Brilliance 55 against 98 for the T73 Round Brilliant in GGG: 43 points lower
Brilliance is the share of the 3,200 census rays that enter the stone and come back out of the crown towards the viewer. In GGG, whose critical angle is 30.5°, the Old Single Cut returns 55 of 100 and the T73 98. The Old Single Cut's pavilion mains sit at 48.5°, the T73's at 40.8°. The maps below show where each stone's light returns from and where it leaks.
Old Single Cut in GGG · Brilliance 55
T73 Round Brilliant in GGG · Brilliance 98
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.
Scintillation 44 against 80 for the T73 Round Brilliant in GGG: 36 points lower
Scintillation follows the number of facets the stone shows: 100 × (1 − e^(−facets / 45)). The Old Single Cut has 26 facets and the T73 73, so 44 against 80. 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.
What helps:the DG-Miliano reads 98 for scintillation in GGG, the best of the cuts we score there.
Leakage 36 against 2 for the T73 Round Brilliant in GGG: 34 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 Old Single Cut leaks 36% in GGG against 2% for the T73 in GGG. Grey in the maps below is leaking light; the share under each picture is that picture's own.
Old Single Cut in GGG · Leakage 36
0° · 34% leak
10° · 39% leak
20° · 38% leak
30° · 37% leak
T73 Round Brilliant in GGG · Leakage 2
0° · 0% leak
10° · 4% leak
20° · 14% leak
30° · 23% 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.
Pick the Old Single Cut in GGG for this: it shows more fire than the T73. The catch: it weighs more than in diamond, returns less light than the T73, has fewer facets to sparkle with and leaks more light than the T73.
If that catch matters more to you, the DG-Broken Hearts and Arrows reads 98 for brilliance 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 Old Single Cut model we traced.
Old Single Cut GGG: questions
Is the Old Single a good cut for GGG?
In our census the Old Single Cut returns 55 of 100 for brilliance and 89 for fire in GGG, against 98 and 76 for the T73 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 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 Old Single Cut's pavilion mains sit at 48.5°.
How much does a Old Single weigh in GGG?
At 6.5 mm across, 2.11 ct in GGG, against 1.05 ct for the same cut in diamond (+100%): GGG's specific gravity is 7.05, diamond's 3.52.
Can I see the Old Single 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 Old Single Cut files
6 formatsMillimetersWatertight
Old Single Cut 3D files
The Old Single Cut as exact geometry: 26 planar facets, real-world scale, ready for CAD,
rendering, printing and casting.
Save with a bundle: the Old Single Cut 3D and cutting files are also in Historic Cuts Complete, 6 cuts for €29.99 until 1 December, then €39.99 (€101.88 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).
