T57 Round Brilliant Diamond: the 1919 plan, level with the modern round on light
Brilliance 92 · Fire 79 · Scintillation 72 · in our census, where the T73 scores 93 · 78 · 80 in diamond
The 57-facet round with a knife-edge girdle, the historical baseline of the modern brilliant. In diamond it matches the T73 on light and trails it only on sparkle.
Rendered in our 3D Gemstone Simulator from the T57 Round Brilliant model, 1.00 ct, studio light.
T57 Round Brilliant Diamond
Nothing has been added to the T57's plan since its proportions were published in 1919: a table, eight stars, eight bezels, sixteen upper halves, eight pavilion mains and sixteen lower halves, meeting at a knife-edge girdle. Measured, the T57 model is 59.2% deep over a 40.75° pavilion.
The T73 Round Brilliant is the same plan with a sixteen-facet girdle band, so this comparison isolates the girdle. The result is one con, scintillation, and nothing else that clears our margins.
Is a T57 round brilliant still a good diamond cut? Pros and cons
Pros
None by our margins: light, fire and leakage are level with the T73.
Compared 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 T73
At a glance: the T57 Round Brilliant 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.
Global89, the comparison 90, difference −1
Brilliance92, the comparison 93, difference −1
Fire79, the comparison 78, difference +1
Scintillation72, the comparison 80, difference −8
Spread101, the comparison 100, difference +1
Symmetry100, the comparison 100, difference 0
Shape-norm99, the comparison 100, difference −1
Tilt90, 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.
Nothing beats the T73 by our thresholds. Fire edges ahead, 79 against 78, and spread reads 101 against 100; both are inside our margins. What the T57 offers is history and a slimmer profile: without a girdle band the model is 59.2% deep against the T73's 61.7%, so a 6.5 mm stone weighs 0.92 ct.
Where the T57 trails the modern round
Less scintillation than the T73
Scintillation 72 against 80 for the T73 Round Brilliant in diamond: 8 points lower
With no girdle facets, the T57 has 57 facets to the T73's 73, and our scintillation score follows that count. Light and fire are untouched; only the number of flashes falls.
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.
Choose the T57 for period work, for teaching the brilliant's history, and for comparison: it is the last step before the faceted girdle became standard. In diamond it gives up no light to the modern round.
The knife edge needs protection in a setting. For a finished ring stone, the T73 Round Brilliant Diamond gives the same light with more sparkle and a girdle to seat; for more sparkle on the same knife edge, the T105 Round Brilliant Diamond.
For a cutter learning the brilliant, it is also the plainest of our rounds: 57 facets, no girdle facets to index, and the main angles every later T-series round keeps.
T57 Round Brilliant Diamond: questions
Is a T57 round brilliant less brilliant than a modern round?
Not by our margins: Brilliance 92 against 93 for the T73, and both leak 2%.
What is the difference between a T57 and a T73?
Sixteen girdle facets. The T73 adds them as a band; the T57 ends in a knife edge. That costs the T57 scintillation, 72 against 80, and nothing else we count.
How many facets does a T57 round brilliant have?
57: a table, eight stars, eight bezels, sixteen upper halves, eight pavilion mains and sixteen lower halves.
What does a 6.5 mm T57 diamond weigh?
About 0.92 ct in our knife-edge model.
Get the T57 Round Brilliant Cut files
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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.
