Octagon Cut Amethyst: Pros, Cons & Light Return

Eight sides, a stepped crown and a pavilion in three tiers: the octagon is the hexagon's profile carried round a regular octagon. Our model has a 60.0% table, a 39.8° crown, a 29.3° pavilion and 61.0% depth, 49 facets in all.

In amethyst it returns 64, within ten points of the T73, and only the cushion and the square brilliant do better among non-round cuts. Its losses are set mostly against the same octagon in diamond: fire, leakage and its hold on light when tipped.

Does an octagon cut suit amethyst? Pros and cons

Pros

A quarter lighter than diamond 0.93 vs 1.23 ct

Cons

A little over a third of the diamond's fire 28 vs 76
Twice the diamond's leakage 36 vs 18
Holds less light when tipped than in diamond 83 vs 97
Fewer flashes than the round 66 vs 80

Compared with the T73 Round Brilliant in amethyst and with the Octagon 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 Octagon 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.

Against the T73 Round Brilliant in amethyst: ahead on 2, level on 2, behind on 4.

Global64, the comparison 70, difference −6
Brilliance64, the comparison 72, difference −8
Fire28, the comparison 36, difference −8
Scintillation66, the comparison 80, difference −14
Spread100, the comparison 100, difference 0
Symmetry100, the comparison 100, difference 0
Shape-norm85, the comparison 77, difference +8
Tilt83, the comparison 80, difference +3

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

What amethyst gains in an octagon

A quarter lighter than diamond

0.93 ct at 6.5 mm, against 1.23 ct for the same cut in diamond (−25%)

Quartz's specific gravity, 2.65, is three quarters of diamond's 3.52, and the octagon's weight follows: the same millimetres, a quarter less on the scale.

A Octagon 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 Octagon Cut page

The octagon's costs in amethyst

A little over a third of the diamond's fire

Fire 28 against 76 for the Octagon Cut in diamond: 48 points lower

The stepped crown has the same facets in both stones, and scores 76 for fire in diamond against 28 here. The amethyst octagon also sits under the T73's fire in its own stone.

Octagon cut in amethyst face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 28) — 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.

Octagon cut in diamond face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 76) — 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: Of the amethyst cuts within ten points of the T73's brilliance, DG-Anteros Amethyst has the most fire, 54, at 82 brilliance.

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

Twice the diamond's leakage

Leakage 36 against 18 for the Octagon Cut in diamond: 18 points higher

Twice the share of light leaves through the back in amethyst as in diamond. The diamond's strip in the picture stays under a quarter grey in every frame.

Octagon cut in amethyst tilted 0 degrees: Light Return map, 22% of the face leaking — 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.

Octagon cut in amethyst tilted 10 degrees: Light Return map, 41% of the face leaking — 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: The share does not change with size, and we have measured no steeper octagon. In a square outline, the Square Cut Amethyst brilliant leaks 29%.

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

Holds less light when tipped than in diamond

Tilt 83 against 97 for the Octagon Cut in diamond: 14 points lower

Tipped by 20°, the diamond octagon keeps nearly all its face-up light; the amethyst one keeps 83. That is still more than the T73 holds in amethyst, 80, so the con is against diamond only.

What helps: The Square Cut Amethyst brilliant holds 84 and the T105 Round Brilliant Amethyst 87, slightly more.

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

Fewer flashes than the round

Scintillation 66 against 80 for the T73 Round Brilliant in amethyst: 14 points lower

Our scintillation score is read from the facet count of the census's model of the cut, and the octagon's plan of broad steps scores 66 to the T73's 80. The number is the same in diamond.

Octagon Cut · 49 facets · Scintillation 66

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: For more sparkle with similar light, the Square Cut Amethyst brilliant scores 78.

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

Who an octagon amethyst suits

Choose the octagon for a geometric amethyst centre stone that should still return plenty of light: it is the third-brightest non-round cut we measure in quartz. Its clean outline suits modern designs.

For a square with a little more light and sparkle, the Square Cut Amethyst brilliant; for the most light in amethyst, DG-M5 Amethyst.

Octagon Cut Amethyst: questions

Is an octagon cut good for amethyst?

Yes, for a geometric cut: Brilliance 64 against 72 for the T73, and Tilt 83. Fire is low, 28.

Octagon or Asscher amethyst?

The octagon returns more light (64 against 60) and leaks less (36% against 39%); the Asscher has more fire (52 against 28) and faces up larger per carat.

What does a 6.5 mm octagon amethyst weigh?

0.93 ct, and 1.23 ct in diamond.

Get the Octagon Cut files

6 formatsMillimetresWatertight

Octagon Cut 3D files

The Octagon Cut as exact geometry: 49 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

Octagon Cut cutting files

The Octagon Cut as a faceting design: 41 + 8 girdles = 49 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 Octagon Cut: specifications, model and files

Octagon Cut Amethyst: eight straight sides at three quarters of diamond's weight