Octagon Cut Diamond: the most light of the stepped cuts we measure in this stone, still short of a round
Brilliance 71 · Fire 76 · Scintillation 66 · in our census, where the T73 scores 93 · 78 · 80 in diamond
Steps above the girdle, three tiers below it, eight sides around. In diamond it returns the most light of our stepped cuts, 71, level by our margins with the Asscher's 69, and still beats the T73 on nothing we count.
Rendered in our 3D Gemstone Simulator from the Octagon Cut model, 1.00 ct, studio light.
Octagon Cut Diamond
Its eight sides carry the same profile as our hexagon: steps on the crown, three tiers on the pavilion. In our model: 49 facets, a 60.0% table under a 39.8° crown, a 29.3° pavilion and 61.0% total depth.
Against the T73 Round Brilliant it has no pros by our margins and four cons. Fire and symmetry are level with the round.
Compared 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 T73
At a glance: the Octagon Cut in diamond (white) against the T73 Round Brilliant in diamond (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 diamond: ahead on 1, level on 2, behind on 5.
Global80, the comparison 90, difference −10
Brilliance71, the comparison 93, difference −22
Fire76, the comparison 78, difference −2
Scintillation66, the comparison 80, difference −14
Spread100, the comparison 100, difference 0
Symmetry100, the comparison 100, difference 0
Shape-norm94, the comparison 100, difference −6
Tilt97, the comparison 92, difference +5
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.
Nothing it does counts as a pro against the T73. Tilt reads 97 against 92, past our threshold, but we count Tilt as a pro only when a stone's brilliance is within 5 points of the round's, and the octagon's, 71 against 93, is not. Fire is level, 76 against 78. What it offers is an even eight-sided outline and the most light of the stepped cuts we measure in diamond, level by our margins with the Asscher.
Where the octagon trails a round
Less light than a round
Brilliance 71 against 93 for the T73 Round Brilliant in diamond: 22 points lower
Head-on, grey covers more than a fifth of the octagon's map, where the T73's has a sliver. The pavilion figure, 29.3°, is far under the 38.9° guide minimum we use for round designs; we have not measured a steeper octagon.
Octagon Cut in diamond · Brilliance 71
T73 Round Brilliant in diamond · Brilliance 93
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: With an eight-sided outline, DG-Octagonal Kite Diamond returns 88, the most of any non-round cut we measure in diamond.
Leakage 18 against 2 for the T73 Round Brilliant in diamond: 16 points higher
The octagon lets 18% of its light out of the back, the T73 only 2%. The strip shows the grey easing at 10° and returning by 30°.
Octagon Cut in diamond · Leakage 18
0° · 21% leak
10° · 15% leak
20° · 19% leak
30° · 23% 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; grey is light leaving through the pavilion. The share under each frame is that picture's own.
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.
What helps: The plan sets it. For a symmetrical outline with more flashes, the Cushion Cut Diamond scores 85.
Face-up size 95 against 100 for the T73 Round Brilliant in diamond (T73 = 100): 5% less face-up area for the same weight
Just past our threshold: at the same carat weight its outline covers a little less area than the T73's. The difference is real on our measure, and small.
Octagon Cut · 6.06 mm at 1.00 ct · Face-up size 95
T73 Round Brilliant · 6.48 mm at 1.00 ct · Face-up size 100
Both stones weigh 1.00 ct in diamond and are drawn to the same scale in millimetres, 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 Asscher Cut Diamond faces up at 102 with a stepped outline; otherwise, compare stones by millimetres.
As stepped cuts go, yes: at 71 it is level with the Asscher by our margins, and no stepped cut we measure does better. A round does: the T73 returns 93.
Octagon or DG-Octagonal Kite diamond?
DG-Octagonal Kite for light (88 against 71) and fire (82); the octagon for flashes, 66 against 60.
Octagon or Asscher cut diamond?
The octagon returns slightly more light (71 against 69). The Asscher leaks less (11%), has more fire and faces up larger for its weight (102 against 95).
What does a 6.5 mm octagon diamond weigh?
1.23 ct in our model, worked out from its measured volume.
Get the Octagon Cut files
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Octagon Cut 3D files
The Octagon Cut as exact geometry: 49 planar facets, real-world scale, ready for CAD,
rendering, printing and casting.
