T57 Round Brilliant Ruby: Measured Pros & Cons

Count the T57's facets and you get the 1919 round brilliant exactly: a table, 8 stars, 8 bezels and 16 upper halves above, 8 mains and 16 lower halves below. In our model the pavilion mains sit at 40.75° and the stone measures 59.2% from table to culet.

In ruby it matches the T73 on light, 94 each, and nearly matches it on leakage, 6% against 5%. It has fewer facets, so less sparkle, and against the same cut in diamond the usual corundum costs apply.

For a cutter, it is the simplest full brilliant to put on a ruby: no girdle facets to index, and a knife edge that needs care on the lap.

Is the T57 a good cut for a ruby? Pros and cons

Pros

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

Cons

Far less fire than the diamond T57 39 vs 79
Keeps less light when tilted than in diamond 74 vs 90
Heavier than a diamond of the same width 1.04 vs 0.92 ct
Less sparkle than the T73 72 vs 80

Compared with the T73 Round Brilliant in ruby 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 ruby (white) against the T73 Round Brilliant in ruby (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 ruby: 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 ruby gains in a T57

Neither the T73 in ruby nor the diamond T57 is beaten on any score by our margins. Brilliance is identical to the T73's, 94, and fire is two points higher, 39 against 37, too small to count. Its case is historical: the plan every modern ruby round grew from, kept for teaching, comparison and period work.

Where the T57 falls short in ruby

Far less fire than the diamond T57

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

The 1919 crown that throws 79 for fire in diamond manages 39 in ruby. Ruby's spectral spread is weak, so few coloured flashes reach the eye even from a well-proportioned crown.

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

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) — 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: No 1919 refinement lifts a ruby's fire much; the elongated Oval Cut Ruby nearly doubles the T57's, at 74.

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

Keeps less light when tilted than in diamond

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

Tilt 74 in ruby, 90 in diamond. The proportions were set for diamond's optics; in a stone with a 34.6° critical angle, tipping lets more of the light out.

T57 round brilliant in ruby 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.

T57 round brilliant in ruby tilted 10 degrees: Light Return map, 11% 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: For a round that holds its light at an angle, DG-Miliano Ruby scores 83 in ruby, against this cut's 74.

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

Heavier than a diamond of the same width

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

Without a girdle band the T57 is a light round, 1.04 ct at 6.5 mm in ruby, but still heavier than the 0.92 ct of a diamond T57.

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

What helps: Choose by millimetres.

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

Less sparkle than the T73

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

57 facets against the T73's 73: the sixteen girdle facets the T73 adds are what the 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: Add the girdle band: the T73 Round Brilliant Ruby scores 80 with the same light, DG-Vitruvio Ruby 98.

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

Who a T57 ruby suits

The T57 suits teaching, comparison and period work in ruby, and anyone who wants the round brilliant in its original form. Its light is a match for the T73's.

For a stone to set, the T73 Round Brilliant Ruby adds sparkle and a girdle a setter can seat. For the brightest ruby round, DG-M5 Ruby.

T57 Round Brilliant Ruby: questions

Is a T57 ruby as bright as a modern round?

Yes. Its Brilliance, 94, ties the T73's in ruby, and it leaks 6% against 5%.

Why does a T57 ruby sparkle less than a T73?

The missing girdle band: 57 facets against 73, so scintillation drops to 72 from the T73's 80.

What does a 6.5 mm T57 ruby weigh?

With no girdle band to carry, about 1.04 ct in ruby and 0.92 ct in diamond.

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

Ruby: optical properties and the top ten cuts · The T57 Round Brilliant: specifications, model and files

T57 Round Brilliant Ruby: the 1919 baseline, as bright as the T73