Brilliance 73 · Fire 51 · Scintillation 78 · in our census, where the T73 scores 86 · 50 · 80 in tourmaline
How the Square Cut handles light in tourmaline, measured: brilliance 73, fire 51 and 20% leakage, set against the T73 in the same stone and against the same cut in diamond.
Tourmaline has a refractive index of 1.603 to 1.655 and a dispersion of 0.017. Its critical angle, from the low end of that range, is 38.6°, so a round design needs a pavilion of at least 38.6° for head-on light to reflect off both sides of the pavilion and leave through the table. We trace it with one index, 1.629, the midpoint of the published range, and a fire spread of 0.015, 0.86 of the published dispersion. Every picture here is our Light Return tracer at 1.603, and every figure is from the same light census that scores the other gemstones; the 3D Gemstone Simulator shows the Square Cut in tourmaline live. Tourmaline is strongly doubly refractive (birefringence up to 0.040), so its back facets can look doubled. Our census traces one index (1.629), so the doubling is not in these figures.
The Square Cut has 69 facets and a total depth of 65.0% of its width; its pavilion mains sit at 41.4°. In tourmaline, the census returns 73 of 100 for brilliance and 51 for fire, against 86 and 50 for the T73, our benchmark, in the same stone; the same Square Cut in diamond reads 85 and 72.
Compared with the T73 Round Brilliant in tourmaline and with the 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.
At a glance: the Square Cut in tourmaline (white) against the T73 Round Brilliant in tourmaline (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 tourmaline: ahead on 3, level on 1, behind on 4.
1.01 ct at 6.5 mm, against 1.14 ct for the same cut in diamond (−11%)
Weight follows specific gravity: 3.13 for tourmaline against 3.52 for diamond, so the same model at the same size weighs 1.01 ct here and 1.14 ct in diamond, 6.5 mm across. Nothing about the light changes with it.
Try it yourself: Weights in every gemstone on the Square Cut page
Fire 51 against 72 for the Square Cut in diamond: 21 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 (0.015 in tourmaline) and counts a ray as fire when the two directions differ by more than 0.6°. The Square Cut reads 51 against 72 for the same cut in diamond. The figure is the census's; the 3D Gemstone Simulator renders tourmaline'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 Square Cut in tourmaline under the sunny-day lighting.
What helps: the Oval Cut reads 80 for fire in tourmaline, the best of the cuts we score there.
Brilliance 73 against 86 for the T73 Round Brilliant in tourmaline: 13 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 tourmaline, whose critical angle is 38.6°, the Square Cut returns 73 of 100 and the T73 86. The Square Cut's pavilion mains sit at 41.4°, the T73's at 40.8°. The maps below show where each stone's light returns from and where it leaks.
Square Cut in tourmaline · Brilliance 73
T73 Round Brilliant in tourmaline · Brilliance 86
What helps: the DG-M5 reads 96 for brilliance in tourmaline, the best of the cuts we score there.
Try it yourself: Open this Light Return map in the simulator
Leakage 20 against 10 for the Square Cut in diamond: 10 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 Square Cut leaks 20% in tourmaline against 10% for the same cut in diamond. Grey in the maps below is leaking light; the share under each picture is that picture's own.
Square Cut in tourmaline · Leakage 20
Square Cut in diamond · Leakage 10
What helps: the DG-M5 reads 4% for leakage in tourmaline, the best of the cuts we score there.
Try it yourself: Tilt it yourself in the simulator's light map
Tilt 83 against 86 for the Square Cut in diamond: 3 points lower
Tilt is how much of its face-up brilliance a stone keeps when the census tilts it 20° about its long axis, with 2,200 rays. The Square Cut keeps 83 against 86 for the same cut in diamond. The tilt strips below show the maps at 0°, 10°, 20° and 30°, with each picture's own leak share under it.
Square Cut in tourmaline · Tilt 83
Square Cut in diamond · Tilt 86
What helps: the DG-Miliano reads 86 for tilt in tourmaline, the best of the cuts we score there.
Try it yourself: Compare the Tilt spoke in the Cut Performance Wheel
Pick the Square Cut in tourmaline for this: it weighs less than in diamond. The catch: it shows less fire than in diamond, returns less light than the T73, leaks more than in diamond and loses more light when tilted than in diamond.
If that catch matters more to you, the Oval Cut reads 80 for fire in tourmaline, 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 Square Cut model we traced.
In our census the Square Cut returns 73 of 100 for brilliance and 51 for fire in tourmaline, against 86 and 50 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.
At least 38.6° for a round design: tourmaline's critical angle is 38.6°, 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 Square Cut's pavilion mains sit at 41.4°.
At 6.5 mm across, 1.01 ct in tourmaline, against 1.14 ct for the same cut in diamond (-11%): tourmaline's specific gravity is 3.13, diamond's 3.52.
Yes: the 3D Gemstone Simulator renders it live, with tourmaline's own refractive index and dispersion. Tourmaline 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.
The Square Cut as exact geometry: 69 planar facets, real-world scale, ready for CAD, rendering, printing and casting.
The Square Cut as a faceting design: 57 + 12 girdles = 69 facets, 64 index, 4-fold mirror-image symmetry, ready for the machine.
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).
Questions before you buy? Email us.
Tourmaline: optical properties and the top ten cuts · The Square Cut: specifications, model and files