Old Single Cut Iolite: lighter than the same cut in diamond

Brilliance 15 · Fire 41 · Scintillation 44 · in our census, where the T73 scores 72 · 58 · 80 in iolite

How the Old Single Cut handles light in iolite, measured: brilliance 15, fire 41 and 79% leakage, set against the T73 in the same stone and against the same cut in diamond.

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The Old Single Cut in iolite, face-up Light Return map from our tracer at refractive index 1.542: red, green and blue show where the light returns from, gray shows where it leaks
Light Return map of the Old Single Cut in iolite, face-up, from our own tracer at refractive index 1.542. Red, green and blue return light to the eye; gray leaks.

Old Single Cut Iolite

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 Old Single Cut in iolite live.

The Old Single Cut has 26 facets, a table of 57.5% of its width and a total depth of 67.5% of its width; its pavilion mains sit at 48.5°. In iolite, the census returns 15 of 100 for brilliance and 41 for fire, against 72 and 58 for the T73, our benchmark, in the same stone; the same Old Single Cut in diamond reads 72 and 84.

Is iolite good in an Old Single? Pros and cons, measured

Pros

Cons

Compared with the T73 Round Brilliant in iolite and with the Old Single 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 Old Single 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.

Performance wheel: Old Single Cut in iolite, against the T73 Round Brilliant in iolite as an outline. Solid white marks where it reaches further, hatching where it falls short. The scores are listed below.50100Global−28Brilliance−57Fire−17Scintillation−36Spread−3Symmetry0Shape-norm−61Tilt+19

Against the T73 Round Brilliant in iolite: ahead on 1, level on 1, behind on 6.

  • Global46, the comparison 74, difference −28
  • Brilliance15, the comparison 72, difference −57
  • Fire41, the comparison 58, difference −17
  • Scintillation44, the comparison 80, difference −36
  • Spread97, the comparison 100, difference −3
  • Symmetry100, the comparison 100, difference 0
  • Shape-norm16, the comparison 77, difference −61
  • Tilt100, the comparison 81, difference +19
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 Old Single Cut gains in iolite

Lighter than the same cut in diamond

0.78 ct at 6.5 mm, against 1.05 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 0.78 ct here and 1.05 ct in diamond, 6.5 mm across. Nothing about the light changes with it.

Iolite0.78 ctDiamond1.05 ct
A Old Single Cut 6.5 mm across, weighed from the model's measured volume and each stone's specific gravity.

Try it yourself: Weights in every gemstone on the Old Single Cut page

What the Old Single Cut gives up in iolite

Leaks more in iolite than in diamond

Leakage 79 against 19 for the Old Single Cut in diamond: 60 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 Old Single Cut leaks 79% in iolite against 19% for the same cut in diamond. Grey in the maps below is leaking light; the share under each picture is that picture's own.

Old Single Cut in iolite · Leakage 79

Old single cut in iolite tilted 0 degrees: Light Return map, 70% of the face leaking0° · 70% leak
Old single cut in iolite tilted 10 degrees: Light Return map, 69% of the face leaking10° · 69% leak
Old single cut in iolite tilted 20 degrees: Light Return map, 65% of the face leaking20° · 65% leak
Old single cut in iolite tilted 30 degrees: Light Return map, 57% of the face leaking30° · 57% leak

Old Single Cut in diamond · Leakage 19

Old single cut in diamond tilted 0 degrees: Light Return map, 23% of the face leaking0° · 23% leak
Old single cut in diamond tilted 10 degrees: Light Return map, 19% of the face leaking10° · 19% leak
Old single cut in diamond tilted 20 degrees: Light Return map, 27% of the face leaking20° · 27% leak
Old single cut in diamond tilted 30 degrees: Light Return map, 35% of the face leaking30° · 35% 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 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

Returns less light than the T73 in iolite

Brilliance 15 against 72 for the T73 Round Brilliant in iolite: 57 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 Old Single Cut returns 15 of 100 and the T73 72. The Old Single Cut's pavilion mains sit at 48.5°, the T73's at 40.8°. The maps below show where each stone's light returns from and where it leaks.

Old single cut in iolite face-up Light Return map: red, green and blue show where the light returns from, gray shows where it leaks (Brilliance 15)

Old Single Cut in iolite · Brilliance 15

T73 round brilliant in iolite face-up Light Return map: red, green and blue show where the light returns from, gray shows where it leaks (Brilliance 72)

T73 Round Brilliant in iolite · Brilliance 72

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 85 for brilliance in iolite, the best of the cuts we score there.

Try it yourself: Open this Light Return map in the simulator

Less fire in iolite than in diamond

Fire 41 against 84 for the Old Single Cut in diamond: 43 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 iolite) and counts a ray as fire when the two directions differ by more than 0.6°. The Old Single Cut reads 41 against 84 for the same cut in diamond. 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 Old Single Cut in iolite under the sunny-day lighting.

What helps: the Oval Cut reads 82 for fire in iolite, the best of the cuts we score there.

Try it yourself: See the fire in the 3D Gemstone Simulator

Fewer facets, less sparkle

Scintillation 44 against 80 for the T73 Round Brilliant in iolite: 36 points lower

Scintillation follows the number of facets the stone shows: 100 × (1 − e^(−facets / 45)). The Old Single Cut has 26 facets and the T73 73, so 44 against 80. It depends on the geometry alone, so it is the same in every stone.

Old Single Cut · 26 facets · Scintillation 44

T73 Round Brilliant · 73 facets · Scintillation 80

Scintillation follows the number of facets: more facets, more and smaller flashes as the stone moves. Compare the facet counts under the drawings; each drawing shows only the crown. Drawn from each cut's own model.

What helps: the DG-Miliano reads 98 for scintillation in iolite, the best of the cuts we score there.

Try it yourself: Compare the Scintillation spoke in the Cut Performance Wheel

Our verdict on the Old Single Cut in iolite

Pick the Old Single Cut in iolite for this: it weighs less than in diamond. The catch: it leaks more than in diamond, returns less light than the T73, shows less fire than in diamond and has fewer facets to sparkle with.

If that catch matters more to you, the DG-M5 reads 15% for leakage 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 Old Single Cut model we traced.

Old Single Cut Iolite: questions

Is the Old Single a good cut for iolite?

In our census the Old Single Cut returns 15 of 100 for brilliance and 41 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 1 pro and 4 cons by our thresholds; the summary above names them.

What pavilion angle does iolite need?

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 Old Single Cut's pavilion mains sit at 48.5°.

How much does a Old Single weigh in iolite?

At 6.5 mm across, 0.78 ct in iolite, against 1.05 ct for the same cut in diamond (-26%): iolite's specific gravity is 2.61, diamond's 3.52.

Can I see the Old Single in iolite in 3D?

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.

Get the Old Single Cut files

6 formatsMillimetersWatertight

Old Single Cut 3D files

The Old Single Cut as exact geometry: 26 planar facets, real-world scale, ready for CAD, rendering, printing and casting.

  • STEPExact faceted solid for CAD
  • 3DMRhino, closed mesh on its own layer
  • STLWatertight mesh for printing and casting
  • OBJMesh for modeling and rendering
  • FBXBlender, 3ds Max, Maya, Cinema 4D, Unity, Unreal
  • GLBWeb, AR and quick previews
€9.99 · Personal useBuy the 3D files
GemCad96 index

Old Single Cut cutting files

The Old Single Cut as a faceting design: 18 + 8 girdles = 26 facets, 96 index, 8-fold mirror-image symmetry, ready for the machine.

  • .ascGemCad design file, 96 index gear
  • .csvTier table: angles, indices and cutting order
  • DiagramPrintable faceting diagram
€6.99 · Personal useBuy the cutting files

Save with a bundle: the Old Single 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.

More gemstones and cuts

Iolite: optical properties and the top ten cuts · The Old Single Cut: specifications, model and files

Other cuts in iolite

The Old Single Cut in other gemstones