Brilliance 52 · Fire 75 · Scintillation 76 · in our census, where the T73 scores 72 · 58 · 80 in iolite
How the Pear Cut handles light in iolite, measured: brilliance 52, fire 75 and 39% leakage, set against the T73 in the same stone and against the same cut in diamond.
Iolite has a refractive index of 1.542 to 1.551 and a dispersion of 0.017. Its critical angle, from the low end of that range, is 40.4°, so a round design needs a pavilion of at least 40.4° for head-on light to reflect off both sides of the pavilion and leave through the table. We trace it with one index, 1.547, 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 1.542, and every figure is from the same light census that scores the other gemstones; the 3D Gemstone Simulator shows the Pear Cut in iolite live.
The Pear Cut has 64 facets and a total depth of 60.0% of its width; its pavilion mains sit at 34.9°. In iolite, the census returns 52 of 100 for brilliance and 75 for fire, against 72 and 58 for the T73, our benchmark, in the same stone; the same Pear Cut in diamond reads 53 and 84.
Compared with the T73 Round Brilliant in iolite and with the Pear 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 Pear Cut in iolite (white) against the T73 Round Brilliant in iolite (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 iolite: ahead on 2, behind on 6.
1.01 ct at 6.5 mm, against 1.37 ct for the same cut in diamond (−26%)
Weight follows specific gravity: 2.61 for iolite against 3.52 for diamond, so the same model at the same size weighs 1.01 ct here and 1.37 ct in diamond, 6.5 mm across. Nothing about the light changes with it.
Try it yourself: Weights in every gemstone on the Pear Cut page
Fire 75 against 58 for the T73 Round Brilliant in iolite: 17 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 (0.015 in iolite) and counts a ray as fire when the two directions differ by more than 0.6°. The Pear Cut reads 75 against 58 for the T73 in iolite. The figure is the census's; the 3D Gemstone Simulator renders iolite'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 Pear Cut in iolite under the sunny-day lighting.
Face-up size 115 against 100 for the T73 Round Brilliant in iolite (T73 = 100): 15% more face-up area for the same weight
Face-up size is the outline's area per carat, measured from each model (T73 = 100): 115 for the Pear 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.
Pear Cut · 9.72 x 6.47 mm at 1.00 ct · Face-up size 115
T73 Round Brilliant · 7.15 mm at 1.00 ct · Face-up size 100
Try it yourself: See its size at 1.00 ct in iolite in the 3D Gemstone Simulator
Tilt 56 against 81 for the T73 Round Brilliant in iolite: 25 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 Pear Cut keeps 56 against 81 for the T73. The tilt strips below show the maps at 0°, 10°, 20° and 30°, with each picture's own leak share under it.
Pear Cut in iolite · Tilt 56
T73 Round Brilliant in iolite · Tilt 81
What helps: the T105 Round Brilliant reads 87 for tilt in iolite, the best of the cuts we score there.
Try it yourself: Compare the Tilt spoke in the Cut Performance Wheel
Brilliance 52 against 72 for the T73 Round Brilliant in iolite: 20 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 iolite, whose critical angle is 40.4°, the Pear Cut returns 52 of 100 and the T73 72. The Pear Cut's pavilion mains sit at 34.9°, the T73's at 40.8°. The maps below show where each stone's light returns from and where it leaks.
Pear Cut in iolite · Brilliance 52
T73 Round Brilliant in iolite · Brilliance 72
What helps: the DG-M5 reads 85 for brilliance in iolite, the best of the cuts we score there.
Try it yourself: Open this Light Return map in the simulator
Leakage 39 against 22 for the Pear Cut in diamond: 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 Pear Cut leaks 39% in iolite against 22% for the same cut in diamond. Grey in the maps below is leaking light; the share under each picture is that picture's own.
Pear Cut in iolite · Leakage 39
Pear Cut in diamond · Leakage 22
What helps: the DG-M5 reads 15% for leakage in iolite, the best of the cuts we score there.
Try it yourself: Tilt it yourself in the simulator's light map
Symmetry 85 against 100 for the T73 Round Brilliant in iolite: 15 points lower
Symmetry reads how evenly the pavilion facets of each design family are cut: 100 − 6 × their scatter in degrees. The Pear Cut reads 85, the T73 100. It depends on the geometry alone, so it is the same in every stone.
Pear Cut · 64 facets · Symmetry 85
T73 Round Brilliant · 73 facets · Symmetry 100
Try it yourself: Compare the Symmetry spoke in the Cut Performance Wheel
Pick the Pear Cut in iolite for this: it weighs less than in diamond, shows more fire than the T73 and faces up larger for its weight. The catch: it loses more of its light when tilted, returns less light than the T73, leaks more than in diamond and has a less regular pavilion than the T73.
If that catch matters more to you, the T105 Round Brilliant reads 87 for tilt in iolite, 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 Pear Cut model we traced.
In our census the Pear Cut returns 52 of 100 for brilliance and 75 for fire in iolite, against 72 and 58 for the T73 in the same stone. Against that round and against the same cut in diamond it has 3 pros and 4 cons by our thresholds; the summary above names them.
At least 40.4° for a round design: iolite's critical angle is 40.4°, 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 Pear Cut's pavilion mains sit at 34.9°.
At 6.5 mm across, 1.01 ct in iolite, against 1.37 ct for the same cut in diamond (-26%): iolite's specific gravity is 2.61, diamond's 3.52.
Yes: the 3D Gemstone Simulator renders it live, with iolite's own refractive index and dispersion. Iolite 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 Pear Cut as exact geometry: 64 planar facets, real-world scale, ready for CAD, rendering, printing and casting.
The Pear Cut as a faceting design: 50 + 14 girdles = 64 facets, 64 index, 1-fold mirror-image symmetry, ready for the machine.
Save with a bundle: the Pear Cut 3D files are also in Jewelry Essentials 3D, 10 cuts for €29.99 until 1 December, then €39.99 (€99.90 as single files). Buy the bundle.
Save with a bundle: the Pear 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.
Iolite: optical properties and the top ten cuts · The Pear Cut: specifications, model and files