Octagon Cut Sapphire: more light than the diamond octagon, and little fire

Brilliance 78 · Fire 33 · Scintillation 66 · in our census, where the T73 scores 94 · 37 · 80 in sapphire

Eight sides over a three-tier pavilion: in sapphire the octagon returns more light than it does in diamond, and keeps far less of the diamond's fire.

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

Octagon Cut Sapphire

Take the hexagon's tiers, a stepped crown over a three-tier pavilion, and lay them on eight sides: that is the octagon. In our model that means 49 facets, with a 60.0% table and a 39.8° crown over a 29.3° pavilion, at 61.0% total depth.

In sapphire it returns as much light as the square brilliant, and more than the emerald cut or the Asscher. No score counts as a pro by our margins, though: the T73 returns more light, and the diamond octagon far more fire.

Is an octagon cut worth it in sapphire? Pros and cons

Pros

None by our margins. Its light tops the diamond octagon's but not the T73's.

Cons

Compared with the T73 Round Brilliant in sapphire 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 sapphire (white) against the T73 Round Brilliant in sapphire (dashed): solid white where it reaches further, hatched where it falls short. Each pro and con is explained, with pictures, below.

Performance wheel: Octagon Cut in sapphire, against the T73 Round Brilliant in sapphire as an outline. Solid white marks where it reaches further, hatching where it falls short. The scores are listed below.50100Global−7Brilliance−16Fire−4Scintillation−14Spread0Symmetry0Shape-norm+1Tilt+12

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

  • Global72, the comparison 79, difference −7
  • Brilliance78, the comparison 94, difference −16
  • Fire33, the comparison 37, difference −4
  • Scintillation66, the comparison 80, difference −14
  • Spread100, the comparison 100, difference 0
  • Symmetry100, the comparison 100, difference 0
  • Shape-norm103, the comparison 102, difference +1
  • Tilt87, the comparison 75, difference +12
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 a sapphire gains as an octagon

No score counts as a pro: each is set against its wider gap, and Tilt has a rule of its own. Against the diamond octagon, sapphire returns more light, 78 against 71, but the gap to the T73's 94 is the wider one, so brilliance is a con. Tipped 20°, it keeps 87 of its light against the T73's 75, but we count Tilt as a pro only when Brilliance is within five points of the baseline, and here it is 78 against 94; against the diamond octagon's 97 it counts as a con, though not among the four largest shown. What it offers is a crisp eight-sided outline with a fair share of a round's light.

Where the octagon falls short in sapphire

Far less fire than the diamond octagon

Fire 33 against 76 for the Octagon Cut in diamond: 43 points lower

33 against 76. It is one of the lower fire scores in our sapphire census, below even the T73's 37.

Octagon cut in sapphire face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 33)

Octagon Cut in sapphire · Fire 33

Octagon cut in diamond face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 76)

Octagon Cut in diamond · Fire 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: DG-M5 Sapphire keeps a round's full light and still beats the octagon on fire, 39.

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

Short of the T73's light by about a sixth

Brilliance 78 against 94 for the T73 Round Brilliant in sapphire: 16 points lower

Brilliance 78 against 94, level with the square brilliant in sapphire. In diamond the octagon returns 71, so sapphire suits this design a little better.

Octagon cut in sapphire face-up Light Return map: red, green and blue show where the light returns from, grey shows where it leaks (Brilliance 78)

Octagon Cut in sapphire · Brilliance 78

T73 round brilliant in sapphire face-up Light Return map: red, green and blue show where the light returns from, grey shows where it leaks (Brilliance 94)

T73 Round Brilliant in sapphire · Brilliance 94

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: A cushion or a round returns more in sapphire: the Cushion Cut Sapphire 88, DG-Vitruvio Sapphire 94.

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

A fifth of the light leaks

Leakage 20 against 5 for the T73 Round Brilliant in sapphire: 15 points higher

A fifth of what enters, 20%, is lost through the back in our census; the T73 loses 5%. The pavilion figure, 29.3°, sits under sapphire's 34.6° critical angle and its 36.4° guide minimum.

Octagon Cut in sapphire · Leakage 20

Octagon cut in sapphire tilted 0 degrees: Light Return map, 18% of the face leaking0° · 18% leak
Octagon cut in sapphire tilted 10 degrees: Light Return map, 21% of the face leaking10° · 21% leak
Octagon cut in sapphire tilted 20 degrees: Light Return map, 31% of the face leaking20° · 31% leak
Octagon cut in sapphire tilted 30 degrees: Light Return map, 34% of the face leaking30° · 34% leak

T73 Round Brilliant in sapphire · Leakage 5

T73 round brilliant in sapphire tilted 0 degrees: Light Return map, 1% of the face leaking0° · 1% leak
T73 round brilliant in sapphire tilted 10 degrees: Light Return map, 10% of the face leaking10° · 10% leak
T73 round brilliant in sapphire tilted 20 degrees: Light Return map, 29% of the face leaking20° · 29% leak
T73 round brilliant in sapphire tilted 30 degrees: Light Return map, 30% of the face leaking30° · 30% 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: We have no measurement of a steeper octagon. Among squares in sapphire, the Square Cut Sapphire leaks 16%.

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

Fewer flashes than a round

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

Scintillation 66 against 80, with 49 facets against 73. The diamond octagon scores the same 66: sparkle here is the facet plan, not the stone.

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.

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

Who an octagon sapphire suits

The octagon suits a sapphire in a modern, geometric setting where a crisp outline and a fair share of light matter more than fire.

It returns more light than the Hexagon Cut Sapphire (64) and DG-Octagonal Kite Sapphire (74). For more light than any of the three, choose a round: DG-M5 Sapphire or DG-Vitruvio Sapphire.

Octagon Cut Sapphire: questions

Is an octagon cut good for sapphire?

It is one of the brighter fancy shapes in sapphire, Brilliance 78, but it trails the T73's 94 and shows little fire, 33.

Octagon or Asscher for a sapphire?

The octagon returns more light (78 against 68) and leaks less (20% against 29%); the Asscher has more fire, 53 against 33.

What does a 6.5 mm octagon sapphire weigh?

About 1.40 ct; in diamond the same octagon is 1.23 ct.

Does an octagon sapphire face up small?

A little, for its weight: Face-up size 95 against 100 for the T73, both measured from the model outline.

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

Sapphire: optical properties and the top ten cuts · The Octagon Cut: specifications, model and files

Other cuts in sapphire

The Octagon Cut in other gemstones