Peruzzi Cut Spinel: what our light census measures
Brilliance 44 · Fire 28 · Scintillation 81 · in our census, where the T73 scores 94 · 47 · 80 in spinel
How the Peruzzi Cut handles light in spinel, measured: brilliance 44, fire 28 and 54% leakage, set against the T73 in the same stone and against the same cut in diamond.
Light Return map of the Peruzzi 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.
Peruzzi 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 Peruzzi Cut in spinel 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 spinel, the census returns 44 of 100 for brilliance and 28 for fire, against 94 and 47 for the T73, our benchmark, in the same stone; the same Peruzzi Cut in diamond reads 75 and 68.
Is spinel good in a Peruzzi? Pros and cons, measured
Compared with the T73 Round Brilliant in spinel 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.
All eight scores against the T73
At a glance: the Peruzzi 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, behind on 6.
Global58, the comparison 81, difference −23
Brilliance44, the comparison 94, difference −50
Fire28, the comparison 47, difference −19
Scintillation81, the comparison 80, difference +1
Spread96, the comparison 100, difference −4
Symmetry85, the comparison 100, difference −15
Shape-norm69, the comparison 101, difference −32
Tilt100, the comparison 75, difference +25
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 Peruzzi Cut gains in spinel
Against the T73 in spinel and the same cut in diamond, no figure of the Peruzzi Cut is ahead by the thresholds above. Its figures are in the wheel and the FAQ; Spinel ranks every cut we score in spinel.
What the Peruzzi Cut gives up in spinel
Returns less light than the T73 in spinel
Brilliance 44 against 94 for the T73 Round Brilliant in spinel: 50 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 Peruzzi Cut returns 44 of 100 and the T73 94. 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 spinel · Brilliance 44
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 54 against 6 for the T73 Round Brilliant in spinel: 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 54% 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.
Peruzzi Cut in spinel · Leakage 54
0° · 54% leak
10° · 51% leak
20° · 42% leak
30° · 32% 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.
Fire 28 against 68 for the Peruzzi Cut in diamond: 40 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 (0.017 in spinel) and counts a ray as fire when the two directions differ by more than 0.6°. The Peruzzi Cut reads 28 against 68 for the same cut in diamond. 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 Peruzzi Cut in spinel under the sunny-day lighting.
What helps:the DG-Elongated Hexagon reads 80 for fire in spinel, the best of the cuts we score there.
Symmetry 85 against 100 for the T73 Round Brilliant in spinel: 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
Symmetry scores how regular the pavilion facets are within the design. Compare how evenly the facets repeat around each pavilion. Drawn from each cut's own model.
Against the T73 in spinel and the same cut in diamond, no figure of the Peruzzi Cut is ahead by our thresholds. 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 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 Peruzzi Cut model we traced.
Peruzzi Cut Spinel: questions
Is the Peruzzi a good cut for spinel?
In our census the Peruzzi Cut returns 44 of 100 for brilliance and 28 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 0 pros and 4 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 Peruzzi Cut's pavilion mains sit at 46.2°.
How much does a Peruzzi weigh in spinel?
At 6.5 mm across, 1.36 ct in spinel, against 1.32 ct for the same cut in diamond (+3%): spinel's specific gravity is 3.62, diamond's 3.52.
Can I see the Peruzzi 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 Peruzzi Cut files
6 formatsMillimetersWatertight
Peruzzi Cut 3D files
The Peruzzi Cut as exact geometry: 74 planar facets, real-world scale, ready for CAD,
rendering, printing and casting.
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).
