Old Single Cut Diamond: Pros, Cons & Fire

The single cut, or eight cut, is a table, a ring of crown facets and a ring of pavilion mains on an octagonal outline. Our model has 26 facets, a 57.5% table and a steep 48.48° pavilion. We traced it in diamond with the census behind every score on this site and set it against the T73 Round Brilliant, our modern round.

Is an Old Single cut diamond any good? Pros and cons

Pros

More fire than the modern round 84 vs 78

Cons

Far fewer flashes as it moves 44 vs 80
Less light back to the eye 72 vs 93
Light escapes through the pavilion 19 vs 2
A little smaller for its weight 97 vs 100

Compared with the T73 Round Brilliant in diamond 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 diamond (white) against the T73 Round Brilliant in diamond (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 diamond: ahead on 2, level on 1, behind on 5.

Global79, the comparison 90, difference −11
Brilliance72, the comparison 93, difference −21
Fire84, the comparison 78, difference +6
Scintillation44, the comparison 80, difference −36
Spread97, the comparison 100, difference −3
Symmetry100, the comparison 100, difference 0
Shape-norm78, the comparison 100, difference −22
Tilt94, the comparison 92, difference +2

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 diamond gains in an Old Single cut

More fire than the modern round

Fire 84 against 78 for the T73 Round Brilliant in diamond: 6 points higher

With so few facets every flash is large, and more of the light that does come back is split into colour. It is the one score where this old plan beats the T73 in diamond.

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) — 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.

T73 round brilliant in diamond face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 78) — 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.

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

Where the Old Single falls short in diamond

Far fewer flashes as it moves

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

Our scintillation score follows the facet count: 26 facets against the T73's 73. Expect a slow, bold sparkle rather than the fine glitter of a modern round.

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: Nothing in the angles changes this: it is the facet plan. For the antique look with more sparkle, the Old European Cut Diamond scores 81 for scintillation.

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

Less light back to the eye

Brilliance 72 against 93 for the T73 Round Brilliant in diamond: 21 points lower

Fewer facets catch less of the light that enters. The face-up maps show the difference: the T73's face is almost all colour, the Old Single's has grey wedges round its rim.

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

T73 round brilliant in diamond face-up Light Return map: red, green and blue show where the light returns from, grey shows where it leaks (Brilliance 93) — 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: Among the antique rounds, the Old European Cut Diamond comes closest to the T73, at 90. For the most light, the T73 Round Brilliant itself.

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

Light escapes through the pavilion

Leakage 19 against 2 for the T73 Round Brilliant in diamond: 17 points higher

Nearly a fifth of the light in our census leaves through the back. The grey in every frame of the tilt strip is that leak; in the T73 it barely appears until the stone tips past 20°.

Old single cut in diamond tilted 0 degrees: Light Return map, 24% 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.

Old single cut in diamond tilted 10 degrees: Light Return map, 19% 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: Size does not help: the same angles leak the same share at any size. The Old European Cut leaks 5% in diamond, the T73 2%.

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

A little smaller for its weight

Spread 97 against 100 for the T73 Round Brilliant in diamond: 3 points lower

At 67.5% deep it carries more weight below the girdle than the T73, so a stone of the same carat weight is slightly narrower across.

Old Single Cut · 6.39 mm at 1.00 ct · Spread 97

T73 Round Brilliant · 6.48 mm at 1.00 ct · Spread 100

Both stones weigh 1.00 ct in diamond and are drawn to the same scale, from each cut's own model. Spread is face-up size per carat: a deeper stone carries more weight below the girdle and looks smaller for its weight.

What helps: Compare stones by millimetres, not carats: a 6.5 mm Old Single weighs 1.05 ct in diamond.

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

Who an Old Single cut diamond suits

Choose it for small accent stones and for collections of early cuts, where large, slow flashes and plenty of colour are the point. The fire figure backs the colour; the facet count explains the boldness.

If brightness matters most, pick something else: the T73 Round Brilliant returns more light and sparkles more finely, and the Old European Cut Diamond gives an antique round at 90 brilliance.

Old Single Cut Diamond: questions

Is an Old Single cut diamond less brilliant than a round brilliant?

Yes, in our census: Brilliance 72 against 93 for the T73 Round Brilliant, with 19% of the light leaking against 2%.

Does an Old Single cut diamond have more fire?

It does: Fire 84 against 78. Fewer, larger facets turn more of the returned light into colour.

How many facets does an Old Single cut have?

Our model has 26, against 73 on the T73. That is why its scintillation scores 44 against 80.

What does a 6.5 mm Old Single cut diamond weigh?

About 1.05 ct, from the model's measured volume and diamond's specific gravity of 3.52.

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.

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

Old Single Cut Diamond: more fire than a modern round, from 26 facets