T57 Round Brilliant Emerald: lighter in weight than diamond, with the T73's light in this stone

Brilliance 78 · Fire 40 · Scintillation 72 · in our census, where the T73 scores 78 · 39 · 80 in emerald

The knife-edge 1919 round, the teaching baseline of the modern brilliant: in emerald it returns exactly the T73's light.

See it in the simulatorGet the files
The T57 Round Brilliant in emerald, 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 Emerald

The T57 is the round brilliant with nothing added: table, 8 stars, 8 bezels, 16 upper halves, 8 pavilion mains and 16 lower halves, meeting at a knife-edge girdle. The mains are cut at 40.75°, and with no girdle band the stone stands just 59.2% from table to point.

We keep it for teaching, comparison and period work, and in emerald it earns its place in the comparison: Brilliance 78, the same as the T73, with 22% leakage, also the same. Every con below is the gap to the same T57 in diamond.

That makes the T57 a clean test of what emerald itself does to a round. The proportions were set for diamond; moved into a stone with a refractive index near 1.58 and a dispersion of 0.014, they lose about a sixth of their light and half their fire, and the losses are the stone's, not the plan's.

How does emerald do in a T57 cut? Pros and cons

Pros

Cons

Compared with the T73 Round Brilliant in emerald 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 emerald (white) against the T73 Round Brilliant in emerald (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 emerald, against the T73 Round Brilliant in emerald as an outline. Solid white marks where it reaches further, hatching where it falls short. The scores are listed below.50100Global−1Brilliance0Fire+1Scintillation−8Spread+1Symmetry0Shape-norm0Tilt−1

Against the T73 Round Brilliant in emerald: ahead on 2, level on 3, behind on 3.

  • Global72, the comparison 73, difference −1
  • Brilliance78, the comparison 78, difference 0
  • Fire40, the comparison 39, difference +1
  • Scintillation72, the comparison 80, difference −8
  • Spread101, the comparison 100, difference +1
  • Symmetry100, the comparison 100, difference 0
  • Shape-norm84, the comparison 84, difference 0
  • Tilt76, the comparison 77, 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 emerald gains in a T57

Lighter than a diamond T57

0.71 ct at 6.5 mm, against 0.92 ct for the same cut in diamond (−23%)

A knife-edge stone 59.2% deep, the T57 at 6.5 mm is 0.71 ct in emerald. The same size in diamond is 0.92 ct.

Emerald0.71 ctDiamond0.92 ct
A T57 Round Brilliant 6.5 mm across, weighed from the model's measured volume and each stone's specific gravity.

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

Where the T57 falls short in emerald

About half the diamond version's fire

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

Fire 40 against 79. Emerald's dispersion, 0.014, is the limit; the cut cannot add colour the stone does not split.

T57 round brilliant in emerald face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 40)

T57 Round Brilliant in emerald · Fire 40

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.

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

A fifth of the light leaks

Leakage 22 against 2 for the T57 Round Brilliant in diamond: 20 points higher

Our census loses 22% through the pavilion, where diamond in the same T57 loses 2%. At 39.4°, emerald's critical angle is far wider than diamond's 24.4°.

T57 Round Brilliant in emerald · Leakage 22

T57 round brilliant in emerald tilted 0 degrees: Light Return map, 11% of the face leaking0° · 11% leak
T57 round brilliant in emerald tilted 10 degrees: Light Return map, 35% of the face leaking10° · 35% leak
T57 round brilliant in emerald tilted 20 degrees: Light Return map, 33% of the face leaking20° · 33% leak
T57 round brilliant in emerald tilted 30 degrees: Light Return map, 38% of the face leaking30° · 38% leak

T57 Round Brilliant in diamond · Leakage 2

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
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 changes nothing; the share is fixed by the angles. DG-Anteros Emerald, on the T73's plan with new angles, leaks 14%.

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

Less light than in diamond

Brilliance 78 against 92 for the T57 Round Brilliant in diamond: 14 points lower

Brilliance 78 against 92: well under the diamond version, and level with the T73 in emerald, so the girdle band changes nothing about light.

T57 round brilliant in emerald face-up Light Return map: red, green and blue show where the light returns from, grey shows where it leaks (Brilliance 78)

T57 Round Brilliant in emerald · Brilliance 78

T57 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 92)

T57 Round Brilliant in diamond · Brilliance 92

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: Our twelve-fold DG-M5 Emerald returns 90 in emerald.

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

Holds less light tilted than in diamond

Tilt 76 against 90 for the T57 Round Brilliant in diamond: 14 points lower

76 of the face-up light is kept at 20°, against 90 for a diamond T57.

T57 Round Brilliant in emerald · Tilt 76

T57 round brilliant in emerald tilted 0 degrees: Light Return map, 11% of the face leaking0° · 11% leak
T57 round brilliant in emerald tilted 10 degrees: Light Return map, 35% of the face leaking10° · 35% leak
T57 round brilliant in emerald tilted 20 degrees: Light Return map, 33% of the face leaking20° · 33% leak
T57 round brilliant in emerald tilted 30 degrees: Light Return map, 38% of the face leaking30° · 38% 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.

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

Who a T57 emerald suits

The T57 suits period work and anyone studying how the round brilliant developed. In emerald it gives up nothing in light to the T73, only sparkle (72 against 80) and the faceted girdle.

For a ring stone, the T73 Round Brilliant Emerald has a girdle a setter can seat; for the most light, DG-M5 Emerald.

T57 Round Brilliant Emerald: questions

Is the T57 as good as a modern round in emerald?

For light, yes: Brilliance 78 against 78 for the T73, and the same 22% leakage. It sparkles less, 72 against 80.

Does a T57 emerald have fire?

Little: 40, against 79 for the same cut in diamond.

What does a 6.5 mm T57 emerald weigh?

0.71 ct in our model; a diamond of that width weighs 0.92 ct.

Is a knife-edge girdle a risk in emerald?

A knife edge has no band to take a knock, and emerald, at 7.5 to 8 on the Mohs scale, is softer and more brittle than diamond. A bezel or a protective rim makes sense.

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

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

Other cuts in emerald

The T57 Round Brilliant in other gemstones