Octagon Cut Grossular: what our light census measures
Brilliance 78 · Fire 52 · Scintillation 66 · in our census, where the T73 scores 94 · 58 · 80 in grossular
How the Octagon Cut handles light in grossular, measured: brilliance 78, fire 52 and 21% leakage, set against the T73 in the same stone and against the same cut in diamond.
Light Return map of the Octagon Cut in grossular, face-up, from our own tracer at refractive index 1.73. Red, green and blue return light to the eye; gray leaks.
Octagon Cut Grossular
Grossular has a refractive index of 1.730 to 1.760 and a dispersion of 0.028. Its critical angle, from the low end of that range, is 35.3°, so a round design needs a pavilion of at least 36.2° for head-on light to reflect off both sides of the pavilion and leave through the table. We trace it with one index, 1.745, the midpoint of the published range, and a fire spread of 0.024, 0.86 of the published dispersion. Every picture here is our Light Return tracer at 1.730, and every figure is from the same light census that scores the other gemstones; the 3D Gemstone Simulator shows the Octagon Cut in grossular live.
The Octagon Cut has 49 facets, a table of 60.0% of its width and a total depth of 61.0% of its width; its pavilion mains sit at 29.3°. In grossular, the census returns 78 of 100 for brilliance and 52 for fire, against 94 and 58 for the T73, our benchmark, in the same stone; the same Octagon Cut in diamond reads 71 and 76.
Is grossular good in an Octagon? Pros and cons, measured
Compared with the T73 Round Brilliant in grossular and with the Octagon 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 Octagon Cut in grossular (white) against the T73 Round Brilliant in grossular (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 grossular: ahead on 2, level on 2, behind on 4.
Global75, the comparison 83, difference −8
Brilliance78, the comparison 94, difference −16
Fire52, the comparison 58, difference −6
Scintillation66, the comparison 80, difference −14
Spread100, the comparison 100, difference 0
Symmetry100, the comparison 100, difference 0
Shape-norm102, the comparison 101, difference +1
Tilt86, the comparison 74, difference +12
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 Octagon Cut gains in grossular
Against the T73 in grossular and the same cut in diamond, no figure of the Octagon Cut is ahead by the thresholds above. Its figures are in the wheel and the FAQ; Grossular ranks every cut we score in grossular.
What the Octagon Cut gives up in grossular
Less fire in grossular than in diamond
Fire 52 against 76 for the Octagon Cut in diamond: 24 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 (0.024 in grossular) and counts a ray as fire when the two directions differ by more than 0.6°. The Octagon Cut reads 52 against 76 for the same cut in diamond. The figure is the census's; the 3D Gemstone Simulator renders grossular'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 Octagon Cut in grossular under the sunny-day lighting.
What helps:the DG-Elongated Hexagon reads 90 for fire in grossular, the best of the cuts we score there.
Brilliance 78 against 94 for the T73 Round Brilliant in grossular: 16 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 grossular, whose critical angle is 35.3°, the Octagon Cut returns 78 of 100 and the T73 94. The Octagon Cut's pavilion mains sit at 29.3°, the T73's at 40.8°. The maps below show where each stone's light returns from and where it leaks.
Octagon Cut in grossular · Brilliance 78
T73 Round Brilliant in grossular · Brilliance 94
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 100 for brilliance in grossular, the best of the cuts we score there.
Leakage 21 against 5 for the T73 Round Brilliant in grossular: 16 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 Octagon Cut leaks 21% in grossular against 5% for the T73 in grossular. Grey in the maps below is leaking light; the share under each picture is that picture's own.
Octagon Cut in grossular · Leakage 21
0° · 17% leak
10° · 23% leak
20° · 32% leak
30° · 33% leak
T73 Round Brilliant in grossular · Leakage 5
0° · 0% leak
10° · 14% leak
20° · 28% leak
30° · 31% 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 0% for leakage in grossular, the best of the cuts we score there.
Scintillation 66 against 80 for the T73 Round Brilliant in grossular: 14 points lower
Scintillation follows the number of facets the stone shows: 100 × (1 − e^(−facets / 45)). The Octagon Cut has 49 facets and the T73 73, so 66 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 grossular, the best of the cuts we score there.
Against the T73 in grossular and the same cut in diamond, no figure of the Octagon Cut is ahead by our thresholds. The catch: it shows less fire than in diamond, returns less light than the T73, leaks more light than the T73 and has fewer facets to sparkle with.
If that catch matters more to you, the DG-Elongated Hexagon reads 90 for fire in grossular, 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 Octagon Cut model we traced.
Octagon Cut Grossular: questions
Is the Octagon a good cut for grossular?
In our census the Octagon Cut returns 78 of 100 for brilliance and 52 for fire in grossular, against 94 and 58 for the T73 in the same stone. Against that round and against the same cut in diamond it has 0 pros and 4 cons by our thresholds; the summary above names them.
What pavilion angle does grossular need?
At least 36.2° for a round design: grossular's critical angle is 35.3°, 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 Octagon Cut's pavilion mains sit at 29.3°.
How much does a Octagon weigh in grossular?
At 6.5 mm across, 1.27 ct in grossular, against 1.23 ct for the same cut in diamond (+3%): grossular's specific gravity is 3.64, diamond's 3.52.
Can I see the Octagon in grossular in 3D?
Yes: the 3D Gemstone Simulator renders it live, with grossular's own refractive index and dispersion. Grossular 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 Octagon Cut files
6 formatsMillimetersWatertight
Octagon Cut 3D files
The Octagon Cut as exact geometry: 49 planar facets, real-world scale, ready for CAD,
rendering, printing and casting.
Save with a bundle: the Octagon Cut cutting files are also in Faceter's Classics, 10 cuts for €22.49 until 1 December, then €29.99 (€69.90 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).
