The only cut in the T-series that adds crown and pavilion facets rather than girdle, and the brightest of the four in diamond.
Global score against T57, Tolkowsky’s 1919 ideal, measured the same way in the same material.
Diamondn = 2.417+1.94Ahead
Moissaniten = 2.65+1.85Ahead
Cubic zirconian = 2.16+1.56Ahead
−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 95.2% of its light usefully and leaks 1.38%, the brightest and cleanest pair of figures in the T-series. Its margin over the standard is not evenly split, though: +1.85 comes from facet count and +1.00 from brilliance, while fire and tilt together hand back nearly a point.
That still makes it the only member of the series where any of the result is a design change rather than a finishing one. It pays for it in movement, holding 87.3 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
90.55 against the standard’s 88.61. Facet count carries it: scintillation is worth +1.85 of the +1.94, with brilliance adding +1.00 at 95.2. Fire hands back −0.45 and tilt −0.50.
TermThis cut / standardPoints
Brillianceweight 0.3495.292.3+1.00
Fireweight 0.2076.678.8−0.45
Tiltweight 0.1687.390.4−0.50
Scintillationweight 0.1090.371.8+1.85
Symmetryweight 0.10100.0100.0+0.00
Leakweight 0.10 ↓1.381.88+0.05
Sum of the six terms+1.95
Published Global gap +1.94. The six terms reconstruct it to
0.01 of a point. The difference is rounding in the source figures, not a second method.
In moissanite n = 2.65
Ahead
91.67 against the standard’s 89.82. The extra pavilion families pay at n = 2.65 by closing leak, 7.76% down to 5.64%, worth +0.21, and brilliance adds +0.29. Scintillation again supplies +1.85; tilt costs −0.34 and fire −0.16.
TermThis cut / standardPoints
Brillianceweight 0.3486.185.2+0.29
Fireweight 0.2096.897.5−0.16
Tiltweight 0.1691.193.2−0.34
Scintillationweight 0.1090.371.8+1.85
Symmetryweight 0.10100.0100.0+0.00
Leakweight 0.10 ↓5.647.76+0.21
Sum of the six terms+1.85
Published Global gap +1.85. The six terms reconstruct it to
0.00 of a point. The difference is rounding in the source figures, not a second method.
In cubic zirconia n = 2.16
Ahead
93.33 against the standard’s 91.77. At n = 2.16 there is nothing left to win on light: the standard already returns 98.0% and leaks 0.51%, and T105’s +0.11 on brilliance sits inside the engine’s resolution. Effectively all of the +1.56 is facet count, against −0.33 of fire.
TermThis cut / standardPoints
Brillianceweight 0.3498.498.0+0.11
Fireweight 0.2085.286.8−0.33
Tiltweight 0.1686.987.2−0.04
Scintillationweight 0.1090.371.8+1.85
Symmetryweight 0.10100.0100.0+0.00
Leakweight 0.10 ↓0.900.51−0.04
Sum of the six terms+1.56
Published Global gap +1.56. The six terms reconstruct it to
0.00 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, BL-Vitruvio 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. Brilliance goes from 92.3 to 95.2 and leak from 1.88% to 1.38%. Both are the best figures in the T-series.
Where it gives ground
Tilt, in all three materials. T105 holds 87.3 under a 20° tilt in diamond against the standard’s 90.4, 91.1 in moissanite against 93.2, and 86.9 in cubic zirconia against 87.2. It is the weakest tilt figure in the T-series. Fire is the second deficit, behind the standard in all three materials.
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 in the series. On a hand, BL-Rafaello gives up 1.3 points of brilliance to hold 9.6 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.
Scintillation
The one term that is not ray-traced. It is a closed formula on the cut’s active facet count, 100(1 − e−n/45), at a tenth of the weight. Planes buried inside the solid form no facet and are not counted. The standard has 57 facets, fewer than anything else here, so every finely cut stone banks this term before a ray is traced. Each cut page reports its margin with the term removed.
Tilt
A retention figure, the share of face-up return the cut still delivers at 20°, capped at 100. It is a ratio, so read it beside the absolute return rather than on its own: a dim cut has less to lose and keeps a higher share of it.
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.