T73 Round Brilliant Sapphire: Pros & Cons

Every other sapphire page on this site sets its cut against the T73. Here the T73 is set against the T57, the 1919 plan it finishes with sixteen girdle facets: the same proportions, 73 facets against 57.

In sapphire the two return the same light, 94 against 94, and the girdle facets lift the sparkle score. The cons come from the T73 in diamond, where only the material differs.

The pavilion sits at 40.75°, a little over four degrees above sapphire's guide minimum of 36.4°.

Is the T73 round brilliant right for sapphire? Pros and cons

Pros

More sparkle than the T57 80 vs 72

Cons

A fraction of the diamond's fire 37 vs 78
Loses light quickly once tipped 75 vs 92
Heavier than diamond at every size 1.15 vs 1.01 ct
A little more leakage than diamond 5 vs 2

Compared with the T57 Round Brilliant in sapphire and with the T73 Round Brilliant 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 T57

At a glance: the T73 Round Brilliant in sapphire (white) against the T57 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.

Against the T57 Round Brilliant in sapphire: ahead on 4, level on 2, behind on 2.

Global79, the comparison 78, difference +1
Brilliance94, the comparison 94, difference 0
Fire37, the comparison 39, difference −2
Scintillation80, the comparison 72, difference +8
Spread100, the comparison 101, difference −1
Symmetry100, the comparison 100, difference 0
Shape-norm102, the comparison 101, difference +1
Tilt75, the comparison 74, difference +1

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 a sapphire gains in the T73

More sparkle than the T57

Scintillation 80 against 72 for the T57 Round Brilliant in sapphire: 8 points higher

Sixteen girdle facets lift the count to 73, and our scintillation score follows the count. The face-up pattern is otherwise the T57's.

T73 Round Brilliant · 73 facets · Scintillation 80

T57 Round Brilliant · 57 facets · Scintillation 72

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

What sapphire costs the T73

A fraction of the diamond's fire

Fire 37 against 78 for the T73 Round Brilliant in diamond: 41 points lower

In diamond the T73 scores 78 for fire, in sapphire 37. Same cut, same light; the gap is corundum's dispersion of 0.018.

T73 round brilliant in sapphire face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 37) — 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.

What helps: Corundum limits every cut. Among rounds, DG-Anteros Sapphire scores 43; the Oval Cut Sapphire 74.

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

Loses light quickly once tipped

Tilt 75 against 92 for the T73 Round Brilliant in diamond: 17 points lower

The strip shows it: a sliver of grey face-up, about a tenth by 10° and close to a third from 20°. The diamond T73 stays under a tenth through 20°, and keeps 92 of its light there against 75 in sapphire.

T73 round brilliant in sapphire tilted 0 degrees: Light Return map, 1% of the face leaking — Tilt is how much of its own face-up light a stone keeps when tilted. 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.

T73 round brilliant in sapphire tilted 10 degrees: Light Return map, 10% of the face leaking — Tilt is how much of its own face-up light a stone keeps when tilted. 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: Of the modern rounds in sapphire, DG-Miliano Sapphire keeps the most when tipped: 83.

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

Heavier than diamond at every size

1.15 ct at 6.5 mm, against 1.01 ct for the same cut in diamond (+14%)

Sapphire is about 14% heavier for the same shape: 1.15 ct at 6.5 mm against 1.01 ct.

A T73 Round Brilliant 6.5 mm across, weighed from the model's measured volume and each stone's specific gravity.

What helps: Specify the stone in millimetres.

Try it yourself: Weights in all seven gemstones on the T73 Round Brilliant page

A little more leakage than diamond

Leakage 5 against 2 for the T73 Round Brilliant in diamond: 3 points higher

5% in our census against 2% for diamond. Head-on, the sapphire map actually shows less grey than the diamond's; the census averages a wider cone of light, and there sapphire falls behind.

What helps: DG-M5 Sapphire leaks 0% and DG-Anteros Sapphire 3% in sapphire. The T73's pavilion is above the guide minimum already, so a steeper one is not the fix our data points to.

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

Who a T73 sapphire suits

The T73 is the safe sapphire round: published proportions, a girdle any setter can seat, and light level with the best classic rounds. It is the reference every other sapphire page here is measured against.

For more light at the same size, DG-M5 Sapphire or DG-Anteros Sapphire. For more sparkle on the T73's light, DG-Vitruvio Sapphire. For the period knife edge, the T57 Round Brilliant Sapphire.

In a strongly dichroic blue, orientation matters as much as the plan: cutters set the table across the optic axis to show the purest blue face-up, and accept some weight loss to do it.

T73 Round Brilliant Sapphire: questions

Is the T73 round brilliant good for sapphire?

It is our benchmark: Brilliance 94, Fire 37 and Scintillation 80 in sapphire, with 5% leakage.

T73 or T57 for a sapphire?

The same light (94 against 94); the T73 sparkles more (80 against 72) and has a girdle a setter can seat.

Why does a round sapphire have so little fire?

Sapphire disperses light at 0.018, under half of diamond's 0.044. The T73 scores 37 in sapphire and 78 in diamond.

What does a 6.5 mm round sapphire weigh?

About 1.15 ct in the T73, against 1.01 ct for a diamond.

Get the T73 Round Brilliant Cut files

6 formatsMillimetresWatertight

T73 Round Brilliant Cut 3D files

The T73 Round Brilliant Cut as exact geometry: 73 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

T73 Round Brilliant Cut cutting files

The T73 Round Brilliant Cut as a faceting design: 57 + 16 girdles = 73 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 T73 Round Brilliant: specifications, model and files

T73 Round Brilliant Sapphire: the benchmark round, with more sparkle than the T57