T57 Round Brilliant Sapphire: the T73's light on the original 57-facet plan

Brilliance 94 · Fire 39 · Scintillation 72 · in our census, where the T73 scores 94 · 37 · 80 in sapphire

The 57-facet plan of 1919, cut in sapphire: as much light as the T73, fewer flashes, and a knife-edge girdle to look after.

See it in the simulatorGet the files
The T57 Round Brilliant in sapphire, rendered at an angle in our 3D Gemstone Simulator under studio light
Rendered in our 3D Gemstone Simulator from the T57 Round Brilliant model, 1.00 ct, studio light.

T57 Round Brilliant Sapphire

The T57 is the round brilliant before the faceted girdle: table, 8 stars, 8 bezels, 16 upper halves, 8 pavilion mains and 16 lower halves, to the proportions published in 1919. Measured, our model has a 40.75° pavilion and a total depth of 59.2%.

In sapphire it returns exactly what the T73 does, 94 for light, and loses a few points of sparkle for want of the girdle facets. The other cons are sapphire's, set against the same cut in diamond.

Is the T57 a good round for sapphire? Pros and cons

Pros

None by our margins: light is level with the T73, Brilliance 94.

Cons

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

At a glance: the T57 Round Brilliant 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: T57 Round Brilliant 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−1Brilliance0Fire+2Scintillation−8Spread+1Symmetry0Shape-norm−1Tilt−1

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

  • Global78, the comparison 79, difference −1
  • Brilliance94, the comparison 94, difference 0
  • Fire39, the comparison 37, difference +2
  • Scintillation72, the comparison 80, difference −8
  • Spread101, the comparison 100, difference +1
  • Symmetry100, the comparison 100, difference 0
  • Shape-norm101, the comparison 102, difference −1
  • Tilt74, the comparison 75, 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 T57

Against neither baseline, the T73 in sapphire or the T57 in diamond, does any score clear our margins. Brilliance ties at 94, and fire, 39 against 37, sits a couple of points over the T73: inside our margin. What the T57 offers is the historical plan itself, for period work, teaching and comparison.

Where the T57 falls short in sapphire

Half the fire of the diamond T57

Fire 39 against 79 for the T57 Round Brilliant in diamond: 40 points lower

The T57 scores 79 in diamond and 39 in sapphire. The facets are identical; corundum simply fans the spectrum out less than half as wide.

T57 round brilliant in sapphire face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 39)

T57 Round Brilliant in sapphire · Fire 39

T57 round brilliant in diamond face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 79)

T57 Round Brilliant in diamond · Fire 79

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 any round; DG-Anteros Sapphire tops our sapphire rounds at 43.

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

Gives up more light when tipped

Tilt 74 against 90 for the T57 Round Brilliant in diamond: 16 points lower

At 20° the sapphire keeps 74 of its face-up light and the diamond 90. Sapphire's lower refractive index lets light through pavilion facets that diamond would reflect.

T57 Round Brilliant in sapphire · Tilt 74

T57 round brilliant in sapphire tilted 0 degrees: Light Return map, 1% of the face leaking0° · 1% leak
T57 round brilliant in sapphire tilted 10 degrees: Light Return map, 11% of the face leaking10° · 11% leak
T57 round brilliant in sapphire tilted 20 degrees: Light Return map, 30% of the face leaking20° · 30% leak
T57 round brilliant in sapphire tilted 30 degrees: Light Return map, 30% of the face leaking30° · 30% leak

T57 Round Brilliant in diamond · Tilt 90

T57 round brilliant in diamond tilted 0 degrees: Light Return map, 4% of the face leaking0° · 4% leak
T57 round brilliant in diamond tilted 10 degrees: Light Return map, 2% of the face leaking10° · 2% leak
T57 round brilliant in diamond tilted 20 degrees: Light Return map, 10% of the face leaking20° · 10% leak
T57 round brilliant in diamond tilted 30 degrees: Light Return map, 16% of the face leaking30° · 16% leak
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: DG-Miliano Sapphire keeps 83 when tilted in sapphire.

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

Heavier than diamond for the size

1.04 ct at 6.5 mm, against 0.92 ct for the same cut in diamond (+14%)

1.04 ct at 6.5 mm in sapphire; the same knife-edge round in diamond is 0.92 ct.

Sapphire1.04 ctDiamond0.92 ct
A T57 Round Brilliant 6.5 mm across, weighed from the model's measured volume and each stone's specific gravity.

What helps: Choose a sapphire by its diameter in millimetres.

Try it yourself: Weights in all seven gemstones on the T57 Round Brilliant page

Fewer flashes than the T73

Scintillation 72 against 80 for the T73 Round Brilliant in sapphire: 8 points lower

57 facets against 73: the sixteen girdle facets the T73 adds are what our scintillation score misses here.

T57 Round Brilliant · 57 facets · Scintillation 72

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: The plan sets this. The T73 Round Brilliant Sapphire adds girdle facets for 80; DG-Vitruvio Sapphire reaches 98 on the same proportions.

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

Who a T57 sapphire suits

The T57 in sapphire suits period reproductions and anyone studying how the brilliant developed. The knife-edge girdle needs a setting that covers it; sapphire is hard, at 9, but an exposed edge can still nick.

For the same light with more sparkle and a seated girdle, the T73 Round Brilliant Sapphire. For more light than either, DG-M5 Sapphire.

T57 Round Brilliant Sapphire: questions

Is the T57 round brilliant good for sapphire?

It returns as much light as the T73, Brilliance 94, but sparkles less: 72 against 80.

Does a T57 sapphire have more fire than a T73?

Barely: 39 against 37, inside our margins. Both are far below diamond's 79 in the T57.

What does a 6.5 mm T57 sapphire weigh?

1.04 ct, tied with the T105 as the lightest of our rounds at that width; a diamond would be 0.92 ct.

Does a T57 sapphire need a special setting?

Its crown and pavilion meet at a knife edge with no girdle band, so a bezel or a closed rim that covers the edge is the safer choice.

Get the T57 Round Brilliant Cut files

6 formatsMillimetresWatertight

T57 Round Brilliant Cut 3D files

The T57 Round Brilliant Cut as exact geometry: 57 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

T57 Round Brilliant Cut cutting files

The T57 Round Brilliant Cut as a faceting design: 57 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 T57 Round Brilliant: specifications, model and files

Other cuts in sapphire

The T57 Round Brilliant in other gemstones