Brilliance 69 · Fire 65 · Scintillation 80 · in our census, where the T73 scores 92 · 47 · 80 in tanzanite
How the Trillion Cut handles light in tanzanite, measured: brilliance 69, fire 65 and 20% leakage, set against the T73 in the same stone and against the same cut in diamond.
Tanzanite has a refractive index of 1.685 to 1.707 and a dispersion of 0.019. Its critical angle, from the low end of that range, is 36.4°, so a round design needs a pavilion of at least 36.4° for head-on light to reflect off both sides of the pavilion and leave through the table. We trace it with one index, 1.696, the midpoint of the published range, and a fire spread of 0.016, 0.86 of the published dispersion. Every picture here is our Light Return tracer at 1.685, and every figure is from the same light census that scores the other gemstones; the 3D Gemstone Simulator shows the Trillion Cut in tanzanite live.
The Trillion Cut has 73 facets, a table of 56.6% of its width and a total depth of 50.7% of its width; its pavilion mains sit at 31.9°. In tanzanite, the census returns 69 of 100 for brilliance and 65 for fire, against 92 and 47 for the T73, our benchmark, in the same stone; the same Trillion Cut in diamond reads 67 and 87.
Compared with the T73 Round Brilliant in tanzanite and with the Trillion 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 Trillion Cut in tanzanite (white) against the T73 Round Brilliant in tanzanite (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 tanzanite: ahead on 3, level on 2, behind on 3.
0.76 ct at 6.5 mm, against 0.80 ct for the same cut in diamond (−5%)
Weight follows specific gravity: 3.35 for tanzanite against 3.52 for diamond, so the same model at the same size weighs 0.76 ct here and 0.80 ct in diamond, 6.5 mm across. Nothing about the light changes with it.
Try it yourself: Weights in every gemstone on the Trillion Cut page
Brilliance 69 against 92 for the T73 Round Brilliant in tanzanite: 23 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 tanzanite, whose critical angle is 36.4°, the Trillion Cut returns 69 of 100 and the T73 92. The Trillion Cut's pavilion mains sit at 31.9°, the T73's at 40.8°. The maps below show where each stone's light returns from and where it leaks.
Trillion Cut in tanzanite · Brilliance 69
T73 Round Brilliant in tanzanite · Brilliance 92
What helps: the DG-M5 reads 100 for brilliance in tanzanite, the best of the cuts we score there.
Try it yourself: Open this Light Return map in the simulator
Fire 65 against 87 for the Trillion Cut in diamond: 22 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 (0.016 in tanzanite) and counts a ray as fire when the two directions differ by more than 0.6°. The Trillion Cut reads 65 against 87 for the same cut in diamond. The figure is the census's; the 3D Gemstone Simulator renders tanzanite'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 Trillion Cut in tanzanite under the sunny-day lighting.
What helps: the DG-Elongated Hexagon reads 79 for fire in tanzanite, the best of the cuts we score there.
Leakage 20 against 8 for the T73 Round Brilliant in tanzanite: 12 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 Trillion Cut leaks 20% in tanzanite against 8% for the T73 in tanzanite. Grey in the maps below is leaking light; the share under each picture is that picture's own.
Trillion Cut in tanzanite · Leakage 20
T73 Round Brilliant in tanzanite · Leakage 8
What helps: the DG-M5 reads 0% for leakage in tanzanite, the best of the cuts we score there.
Try it yourself: Tilt it yourself in the simulator's light map
Pick the Trillion Cut in tanzanite for this: it weighs less than in diamond. The catch: it returns less light than the T73, shows less fire than in diamond and leaks more light than the T73.
If that catch matters more to you, the DG-M5 reads 100 for brilliance in tanzanite, 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 Trillion Cut model we traced.
In our census the Trillion Cut returns 69 of 100 for brilliance and 65 for fire in tanzanite, against 92 and 47 for the T73 in the same stone. Against that round and against the same cut in diamond it has 1 pro and 3 cons by our thresholds; the summary above names them.
At least 36.4° for a round design: tanzanite's critical angle is 36.4°, 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 Trillion Cut's pavilion mains sit at 31.9°.
At 6.5 mm across, 0.76 ct in tanzanite, against 0.80 ct for the same cut in diamond (-5%): tanzanite's specific gravity is 3.35, diamond's 3.52.
Yes: the 3D Gemstone Simulator renders it live, with tanzanite's own refractive index and dispersion. Tanzanite 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 Trillion Cut as exact geometry: 73 planar facets, real-world scale, ready for CAD, rendering, printing and casting.
The Trillion Cut as a faceting design: 61 + 12 girdles = 73 facets, 120 index, 3-fold symmetry, ready for the machine.
Save with a bundle: the Trillion 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).
Questions before you buy? Email us.
Tanzanite: optical properties and the top ten cuts · The Trillion Cut: specifications, model and files