Brilliance 43 · Fire 26 · Scintillation 81 · in our census, where the T73 scores 92 · 47 · 80 in tanzanite
How the Peruzzi Cut handles light in tanzanite, measured: brilliance 43, fire 26 and 56% 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 Peruzzi Cut in tanzanite live.
The Peruzzi Cut has 74 facets, a table of 56.8% of its width and a total depth of 69.1% of its width; its pavilion mains sit at 46.2°. In tanzanite, the census returns 43 of 100 for brilliance and 26 for fire, against 92 and 47 for the T73, our benchmark, in the same stone; the same Peruzzi Cut in diamond reads 75 and 68.
Compared with the T73 Round Brilliant in tanzanite and with the Peruzzi 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 Peruzzi 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 2, behind on 6.
1.25 ct at 6.5 mm, against 1.32 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 1.25 ct here and 1.32 ct in diamond, 6.5 mm across. Nothing about the light changes with it.
Try it yourself: Weights in every gemstone on the Peruzzi Cut page
Brilliance 43 against 92 for the T73 Round Brilliant in tanzanite: 49 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 Peruzzi Cut returns 43 of 100 and the T73 92. The Peruzzi Cut's pavilion mains sit at 46.2°, the T73's at 40.8°. The maps below show where each stone's light returns from and where it leaks.
Peruzzi Cut in tanzanite · Brilliance 43
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
Leakage 56 against 8 for the T73 Round Brilliant in tanzanite: 48 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 Peruzzi Cut leaks 56% 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.
Peruzzi Cut in tanzanite · Leakage 56
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
Fire 26 against 68 for the Peruzzi Cut in diamond: 42 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 Peruzzi Cut reads 26 against 68 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 Peruzzi 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.
Symmetry 85 against 100 for the T73 Round Brilliant in tanzanite: 15 points lower
Symmetry reads how evenly the pavilion facets of each design family are cut: 100 − 6 × their scatter in degrees. The Peruzzi Cut reads 85, the T73 100. It depends on the geometry alone, so it is the same in every stone.
Peruzzi Cut · 74 facets · Symmetry 85
T73 Round Brilliant · 73 facets · Symmetry 100
Try it yourself: Compare the Symmetry spoke in the Cut Performance Wheel
Pick the Peruzzi Cut in tanzanite for this: it weighs less than in diamond. The catch: it returns less light than the T73, leaks more light than the T73, shows less fire than in diamond and has a less regular pavilion 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 Peruzzi Cut model we traced.
In our census the Peruzzi Cut returns 43 of 100 for brilliance and 26 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 4 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 Peruzzi Cut's pavilion mains sit at 46.2°.
At 6.5 mm across, 1.25 ct in tanzanite, against 1.32 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 Peruzzi Cut as exact geometry: 74 planar facets, real-world scale, ready for CAD, rendering, printing and casting.
The Peruzzi Cut as a faceting design: 58 + 16 girdles = 74 facets, 96 index, 4-fold mirror-image symmetry, ready for the machine.
Save with a bundle: the Peruzzi Cut 3D and cutting files are also in Historic Cuts Complete, 6 cuts for €29.99 until 1 December, then €39.99 (€101.88 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 Peruzzi Cut: specifications, model and files