Rectangle Cut Spinel: faces up larger for its weight
Brilliance 40 · Fire 62 · Scintillation 63 · in our census, where the T73 scores 94 · 47 · 80 in spinel
How the Rectangle Cut handles light in spinel, measured: brilliance 40, fire 62 and 53% leakage, set against the T73 in the same stone and against the same cut in diamond.
Light Return map of the Rectangle 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.
Rectangle 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 Rectangle Cut in spinel live.
The Rectangle Cut has 45 facets and a total depth of 62.0% of its width; its pavilion mains sit at 33.5°. In spinel, the census returns 40 of 100 for brilliance and 62 for fire, against 94 and 47 for the T73, our benchmark, in the same stone; the same Rectangle Cut in diamond reads 50 and 77.
Is spinel good in a Rectangle? Pros and cons, measured
Compared with the T73 Round Brilliant in spinel and with the Rectangle 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 Rectangle 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 2, level on 2, behind on 4.
Global61, the comparison 81, difference −20
Brilliance40, the comparison 94, difference −54
Fire62, the comparison 47, difference +15
Scintillation63, the comparison 80, difference −17
Spread100, the comparison 100, difference 0
Symmetry100, the comparison 100, difference 0
Shape-norm53, the comparison 101, difference −48
Tilt84, the comparison 75, difference +9
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 Rectangle Cut gains in spinel
Faces up larger for its weight
Face-up size 121 against 100 for the T73 Round Brilliant in spinel (T73 = 100): 21% more face-up area for the same weight
Face-up size is the outline's area per carat, measured from each model (T73 = 100): 121 for the Rectangle Cut against 100 for the T73. 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.
Rectangle Cut · 7.57 x 5.02 mm at 1.00 ct · Face-up size 121
T73 Round Brilliant · 6.42 mm at 1.00 ct · Face-up size 100
Both stones weigh 1.00 ct in spinel 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.
Fire 62 against 47 for the T73 Round Brilliant in spinel: 15 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 (0.017 in spinel) and counts a ray as fire when the two directions differ by more than 0.6°. The Rectangle Cut reads 62 against 47 for the T73 in spinel. 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 Rectangle Cut in spinel under the sunny-day lighting.
Brilliance 40 against 94 for the T73 Round Brilliant in spinel: 54 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 Rectangle Cut returns 40 of 100 and the T73 94. The Rectangle Cut's pavilion mains sit at 33.5°, the T73's at 40.8°. The maps below show where each stone's light returns from and where it leaks.
Rectangle Cut in spinel · Brilliance 40
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 53 against 6 for the T73 Round Brilliant in spinel: 47 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 Rectangle Cut leaks 53% 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.
Rectangle Cut in spinel · Leakage 53
0° · 54% leak
10° · 59% leak
20° · 63% leak
30° · 63% 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 63 against 80 for the T73 Round Brilliant in spinel: 17 points lower
Scintillation follows the number of facets the stone shows: 100 × (1 − e^(−facets / 45)). The Rectangle Cut has 45 facets and the T73 73, so 63 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.
Pick the Rectangle Cut in spinel for this: it faces up larger for its weight and shows more fire than the T73. The catch: it 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-M5 reads 100 for brilliance 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 Rectangle Cut model we traced.
Rectangle Cut Spinel: questions
Is the Rectangle a good cut for spinel?
In our census the Rectangle Cut returns 40 of 100 for brilliance and 62 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 2 pros and 3 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 Rectangle Cut's pavilion mains sit at 33.5°.
How much does a Rectangle weigh in spinel?
At 6.5 mm across, 2.16 ct in spinel, against 2.10 ct for the same cut in diamond (+3%): spinel's specific gravity is 3.62, diamond's 3.52.
Can I see the Rectangle 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 Rectangle Cut files
6 formatsMillimetersWatertight
Rectangle Cut 3D files
The Rectangle Cut as exact geometry: 45 planar facets, real-world scale, ready for CAD,
rendering, printing and casting.
