Emerald Square Cut Spinel: what our light census measures
Brilliance 73 · Fire 59 · Scintillation 72 · in our census, where the T73 scores 94 · 47 · 80 in spinel
How the Emerald Square Cut handles light in spinel, measured: brilliance 73, fire 59 and 23% leakage, set against the T73 in the same stone and against the same cut in diamond.
Light Return map of the Emerald Square Cut in spinel, face-up, from our own tracer at refractive index 1.712. Red, green and blue return light to the eye; gray leaks.
Emerald Square Cut Spinel
Spinel has a refractive index of 1.712 to 1.747 and a dispersion of 0.020. Its critical angle, from the low end of that range, is 35.7°, so a round design needs a pavilion of at least 36.1° for head-on light to reflect off both sides of the pavilion and leave through the table. We trace it with one index, 1.730, the midpoint of the published range, and a fire spread of 0.017, 0.86 of the published dispersion. Every picture here is our Light Return tracer at 1.712, and every figure is from the same light census that scores the other gemstones; the 3D Gemstone Simulator shows the Emerald Square Cut in spinel live.
The Emerald Square Cut has 49 facets and a total depth of 61.0% of its width; its pavilion mains sit at 28.3°. In spinel, the census returns 73 of 100 for brilliance and 59 for fire, against 94 and 47 for the T73, our benchmark, in the same stone; the same Emerald Square Cut in diamond reads 64 and 84.
Is spinel good in an Emerald Square? Pros and cons, measured
Compared with the T73 Round Brilliant in spinel and with the Emerald Square 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 Emerald Square Cut in spinel (white) against the T73 Round Brilliant in spinel (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 spinel: ahead on 3, level on 1, behind on 4.
Global74, the comparison 81, difference −7
Brilliance73, the comparison 94, difference −21
Fire59, the comparison 47, difference +12
Scintillation72, the comparison 80, difference −8
Spread108, the comparison 100, difference +8
Symmetry100, the comparison 100, difference 0
Shape-norm96, the comparison 101, difference −5
Tilt81, the comparison 75, difference +6
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 Emerald Square Cut gains in spinel
Against the T73 in spinel and the same cut in diamond, no figure of the Emerald Square Cut is ahead by the thresholds above. Its figures are in the wheel and the FAQ; Spinel ranks every cut we score in spinel.
What the Emerald Square Cut gives up in spinel
Less fire in spinel than in diamond
Fire 59 against 84 for the Emerald Square Cut in diamond: 25 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 (0.017 in spinel) and counts a ray as fire when the two directions differ by more than 0.6°. The Emerald Square Cut reads 59 against 84 for the same cut in diamond. The figure is the census's; the 3D Gemstone Simulator renders spinel'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 Emerald Square Cut in spinel under the sunny-day lighting.
What helps:the DG-Elongated Hexagon reads 80 for fire in spinel, the best of the cuts we score there.
Brilliance 73 against 94 for the T73 Round Brilliant in spinel: 21 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 spinel, whose critical angle is 35.7°, the Emerald Square Cut returns 73 of 100 and the T73 94. The Emerald Square Cut's pavilion mains sit at 28.3°, the T73's at 40.8°. The maps below show where each stone's light returns from and where it leaks.
Emerald Square Cut in spinel · Brilliance 73
T73 Round Brilliant in spinel · 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 spinel, the best of the cuts we score there.
Leakage 23 against 6 for the T73 Round Brilliant in spinel: 17 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 Emerald Square Cut leaks 23% in spinel against 6% for the T73 in spinel. Grey in the maps below is leaking light; the share under each picture is that picture's own.
Emerald Square Cut in spinel · Leakage 23
0° · 19% leak
10° · 29% leak
20° · 36% leak
30° · 42% leak
T73 Round Brilliant in spinel · Leakage 6
0° · 0% leak
10° · 15% leak
20° · 30% leak
30° · 32% 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 spinel, the best of the cuts we score there.
Scintillation 72 against 80 for the T73 Round Brilliant in spinel: 8 points lower
Scintillation follows the number of facets the stone shows: 100 × (1 − e^(−facets / 45)). The Emerald Square Cut has 49 facets and the T73 73, so 72 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 spinel, the best of the cuts we score there.
Against the T73 in spinel and the same cut in diamond, no figure of the Emerald Square 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 80 for fire in spinel, 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 Emerald Square Cut model we traced.
Emerald Square Cut Spinel: questions
Is the Emerald Square a good cut for spinel?
In our census the Emerald Square Cut returns 73 of 100 for brilliance and 59 for fire in spinel, against 94 and 47 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 spinel need?
At least 36.1° for a round design: spinel's critical angle is 35.7°, 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 Emerald Square Cut's pavilion mains sit at 28.3°.
How much does a Emerald Square weigh in spinel?
At 6.5 mm across, 1.50 ct in spinel, against 1.46 ct for the same cut in diamond (+3%): spinel's specific gravity is 3.62, diamond's 3.52.
Can I see the Emerald Square in spinel in 3D?
Yes: the 3D Gemstone Simulator renders it live, with spinel's own refractive index and dispersion. Spinel 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 Emerald Square Cut files
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Emerald Square Cut 3D files
The Emerald Square Cut as exact geometry: 49 planar facets, real-world scale, ready for CAD,
rendering, printing and casting.
