Old Single Cut Amethyst: why the eight cut lets most of its light go in quartz

Brilliance 15 · Fire 38 · Scintillation 44 · in our census, where the T73 scores 72 · 36 · 80 in amethyst

Eight crown facets, eight pavilion facets and a steep 48.48° pavilion: in quartz that plan lets nearly four-fifths of the light out of the back.

See it in the simulatorGet the files
The Old Single Cut in amethyst, rendered at an angle in our 3D Gemstone Simulator under studio light
Rendered in our 3D Gemstone Simulator from the Old Single Cut model, 1.00 ct, studio light.

Old Single Cut Amethyst

The single cut is an octahedron with its top sawn off for a table and its corners bevelled to an octagon: one crown angle, one pavilion angle. In our 26-facet model those are 40.0° above the girdle and 48.48° below it, round a 57.5% table, for a stone 67.5% deep.

That pavilion is about eight degrees past amethyst's guide minimum of 40.4°, so a shallow pavilion is not the problem. Light coming straight down reflects off the first steep main, then meets the opposite one too squarely for quartz to hold, and leaves.

Of the cuts we measure in amethyst it leaks the most, 79%, and only DG-Bowtie returns less light.

Is amethyst any good in an Old Single cut? Pros and cons

Pros

Cons

Compared with the T73 Round Brilliant in amethyst and with the Old Single Cut in diamond. A difference counts from 3 points (Brilliance, Fire, Tilt, Leakage), 5 (Scintillation, Symmetry), 2 (Spread) 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 amethyst (white) against the T73 Round Brilliant in amethyst (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 amethyst, against the T73 Round Brilliant in amethyst as an outline. Solid white marks where it reaches further, hatching where it falls short. The scores are listed below.50100Global−25Brilliance−57Fire+2Scintillation−36Spread−3Symmetry0Shape-norm−61Tilt+20

Against the T73 Round Brilliant in amethyst: ahead on 2, level on 1, behind on 5.

  • Global45, the comparison 70, difference −25
  • Brilliance15, the comparison 72, difference −57
  • Fire38, the comparison 36, difference +2
  • 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 80, difference +20
Face-up light census, a different measure from the Cut Grading Tool; Spread and Shape-norm above 100 sit on the ring.
Open it in the Cut Performance Wheel

What amethyst gains in an Old Single cut

A quarter lighter than diamond

0.79 ct at 6.5 mm, against 1.05 ct for the same cut in diamond (−25%)

The eight cut is the deepest round on these pages, 67.5%, which makes it heavy for its width: 0.79 ct at 6.5 mm in amethyst, 1.05 ct in diamond.

Amethyst0.79 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 all seven gemstones on the Old Single Cut page

Why the Old Single fails in amethyst

Nearly four-fifths of the light leaks

Leakage 79 against 19 for the Old Single Cut in diamond: 60 points higher

79% in our census, where the same cut in diamond loses 19%. The diamond's own tilt strip shows grey in every frame; quartz, with its larger critical angle, loses far more.

Old Single Cut in amethyst · Leakage 79

Old single cut in amethyst tilted 0 degrees: Light Return map, 69% of the face leaking0° · 69% leak
Old single cut in amethyst tilted 10 degrees: Light Return map, 69% of the face leaking10° · 69% leak
Old single cut in amethyst tilted 20 degrees: Light Return map, 65% of the face leaking20° · 65% leak
Old single cut in amethyst 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, 24% of the face leaking0° · 24% 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; grey is light leaving through the pavilion. The share under each frame is that picture's own.

What helps: A steeper pavilion is not the answer: at 48.48° it is already far above the guide minimum. The Old European Cut Amethyst leaks 41% in amethyst, DG-M5 Amethyst 15%.

Try it yourself: Tilt it yourself in the simulator's light map

A fifth of the T73's light

Brilliance 15 against 72 for the T73 Round Brilliant in amethyst: 57 points lower

With most of the light gone through the back, little is left for the face to return.

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

Old Single Cut in amethyst · Brilliance 15

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

T73 Round Brilliant in amethyst · Brilliance 72

Red, green and blue = light returning to the eye; grey = light leaving through the pavilion. 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: For an antique round, the Old European Cut Amethyst returns 59; for a modern one, the T73 Round Brilliant Amethyst 72.

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

Under half the diamond version's fire

Fire 38 against 84 for the Old Single Cut in diamond: 46 points lower

Big facets suit fire in diamond, which scores 84 in this cut. In amethyst weak dispersion and heavy leakage leave 38, about the T73's level in this stone.

Old single cut in amethyst face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 38)

Old Single Cut in amethyst · Fire 38

Old single cut in diamond face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 84)

Old Single Cut in diamond · Fire 84

Look at the coloured flashes: those are fire. Same light, same size, same face-up angle; rendered by our 3D Gemstone Simulator from each cut's own model.

What helps: Fire in quartz peaks with the Oval Cut Amethyst, at 69.

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

Few, broad flashes

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

Our scintillation score follows the facet plan, and 26 facets against the T73's 73 give a slow, bold sparkle rather than a glitter.

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. Count the facets in each crown. Drawn from each cut's own model.

What helps: Only more facets change this, and the Old European Cut Amethyst has them: 81.

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

Who an Old Single amethyst suits

We would not cut an Old Single amethyst to be seen for its light. It suits very small accent stones, where a full brilliant would be wasted, and study pieces.

As a first exercise at the faceting machine, its 26 facets and two angles are quick to cut, and amethyst is a forgiving, plentiful stone to learn on. Expect the finished stone to look dark from most angles.

For an antique round in amethyst, the Old European Cut Amethyst; for light, DG-M5 Amethyst.

Old Single Cut Amethyst: questions

Is an Old Single cut good for amethyst?

Not for light: Brilliance 15 against 72 for the T73, and 79% leakage, the most we measure in amethyst.

Why does a steep pavilion leak in amethyst?

Quartz reflects light only when it meets a facet at more than 40.4° from square on. At 48.48°, light that has bounced once meets the far pavilion facet more squarely than that and passes out.

What does a 6.5 mm Old Single amethyst weigh?

0.79 ct; in diamond, 1.05 ct.

Get the Old Single Cut files

6 formatsMillimetresWatertight

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 modelling 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
€9.99 · Personal useBuy the cutting files

Questions before you buy? Email us.

More gemstones and cuts

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

Other cuts in amethyst

The Old Single Cut in other gemstones