The only cut in the T-series that adds crown and pavilion facets rather than girdle, and the brightest stone we measure in diamond.
Global score against T57, Tolkowsky’s 1919 ideal, measured the same way in the same material.
Diamondn = 2.417+3.15Ahead
Moissaniten = 2.65+2.56Ahead
Cubic zirconian = 2.16+2.15Ahead
−6T57 = 0+6
The short version
T105 carries Gabi Tolkowsky’s 105-facet pattern, laid over the family’s 1919 angles. Its own proportions were never published, so the crown and pavilion are Marcel’s: 53% table, 34.5° crown, 40.75° pavilion.
It returns 97.7% of its light usefully and leaks 0.77%, the brightest and cleanest pair of figures of any cut we measure in diamond. Its margin over the standard splits almost exactly in half: +1.84 from brightness, +1.85 from facet count.
That makes it the only member of the series where half the result is a design change rather than a finishing one. It pays for it in movement, holding 86.1 under a 20° tilt against the standard’s 90.4. See the 1919 ideal for how the four T cuts compare.
The ledger
Where the points come from
Global is a weighted sum of six terms. Subtract the standard's figure from this cut's,
term by term, and the six differences add back up to the published gap. Nothing is hidden in the total,
so you can see exactly which part of the stone is doing the work.
In diamond n = 2.417
Ahead
91.76 against the standard's 88.61. Brightness +1.84 and scintillation +1.85, near enough a dead heat between optics and facet count, with leak adding +0.11 at 0.77%. Tilt hands back −0.69, the only term against it.
TermThis cut / standardPoints
Useful lightweight 0.3497.792.3+1.84
Fireweight 0.2079.178.8+0.06
Tiltweight 0.1686.190.4−0.69
Scintillationweight 0.1090.371.8+1.85
Symmetryweight 0.10100.0100.0+0.00
Leakweight 0.10 ↓0.771.88+0.11
Sum of the six terms+3.17
Published Global gap +3.15. The six terms reconstruct it to
0.02 of a point. The difference is rounding in the source figures, not a second method.
In moissanite n = 2.65
Ahead
92.38 against the standard's 89.82. The extra pavilion families earn their keep at n = 2.65: leak falls from 7.76% to 3.78%, worth +0.40, and brightness adds +1.43. Tilt costs −0.90 and fire −0.20.
TermThis cut / standardPoints
Useful lightweight 0.3489.585.3+1.43
Fireweight 0.2096.597.5−0.20
Tiltweight 0.1687.693.2−0.90
Scintillationweight 0.1090.371.8+1.85
Symmetryweight 0.10100.0100.0+0.00
Leakweight 0.10 ↓3.787.76+0.40
Sum of the six terms+2.58
Published Global gap +2.56. The six terms reconstruct it to
0.02 of a point. The difference is rounding in the source figures, not a second method.
In cubic zirconia n = 2.16
Ahead
93.92 against the standard's 91.77. At n = 2.16 there is almost nothing left to win: the standard already returns 98.0% of its light and leaks 0.51%. Brightness manages +0.48, and +1.85 of the +2.15 is facet count.
TermThis cut / standardPoints
Useful lightweight 0.3499.498.0+0.48
Fireweight 0.2087.086.8+0.04
Tiltweight 0.1685.987.1−0.19
Scintillationweight 0.1090.371.8+1.85
Symmetryweight 0.10100.0100.0+0.00
Leakweight 0.10 ↓0.430.51+0.01
Sum of the six terms+2.18
Published Global gap +2.15. The six terms reconstruct it to
0.03 of a point. The difference is rounding in the source figures, not a second method.
What it’s doing
Every other jump in the T-series is girdle. T73 adds 16 vertical facets, T185 adds 128, and a girdle facet stands edge-on to the viewer, so it cannot change where light goes. It buys sparkle count and nothing else.
T105 is the exception. Its 48 extra facets sit on surfaces light passes through: 8 new crown facets at 37°, and 40 new pavilion facets at 41.3°, 42.6° and 43.5°, against the 40.75° mains. That takes the crown to 41 facets and the pavilion to 64.
The result is visible in the one place girdle facets never show up: the light budget. Useful light goes from 92.3% to 97.7% and leak from 1.88% to 0.77%. Both are the best figures in the diamond column.
Where it gives ground
Tilt, in all three materials. T105 holds 86.1 under a 20° tilt in diamond against the standard’s 90.4, 87.6 in moissanite against 93.2, and 85.9 in cubic zirconia against 87.1. It is the weakest tilt figure in the T-series.
The cause is the same geometry that makes it bright. Three of its four new pavilion families sit steeper than Tolkowsky’s mains, up to 43.5°, and a steeper pavilion starts losing light sooner as the stone turns away from the eye. More light dead-on, less light as the hand moves.
Whether that is a good trade depends on where the stone spends its life. Face-up in a tray it is the brightest thing here. On a hand, BL-Rafaello gives up 3.8 points of brightness to hold 10.8 more under tilt.
How to read this
The protocol
Monte-Carlo ray census on exact facet geometry: 3,200 rays face-up plus 2,200 at
20° tilt, cosine-weighted from a 7° near-vertical cone. Every cut is scored against Tolkowsky's 1919 ideal,
measured the same way in the same material.
These are engine estimates, ± 2 points, not lab-certified grades.
A lead of under half a point sits inside the engine's resolution, so we don't claim it as a win. A deficit is reported as a deficit, however small.
Symmetry
Reads 100 for every cut, because each is modelled from exact geometry rather than
a finished stone. It contributes nothing to any comparison here: it cancels, and we show the row anyway.