The widest margin over the 1919 ideal anywhere in the registry, in moissanite, and the price paid for it everywhere else.
Global score against T57, Tolkowsky’s 1919 ideal, measured the same way in the same material.
Diamondn = 2.417−0.82Behind
Moissaniten = 2.65+5.31Ahead
Cubic zirconian = 2.16−4.65Behind
−6T57 = 0+6
The short version
BL-M5 is a single-material design and does not pretend otherwise. In moissanite it returns 98.1% of light usefully against the standard’s 85.3%, and loses 1.05% to leakage against 7.76%. That carries it 5.31 points clear, the largest margin in the registry.
It is also the most honest margin here: only +1.31 of it is facet count, against +4.35 from brilliance alone. In diamond and cubic zirconia it is the weakest cut in the registry and the only one that finishes behind the 1919 ideal in either. Both facts come from the same geometry.
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
Behind
87.79 against the standard's 88.61, the only deficit in the diamond column. The single-cone pavilion aimed at n = 2.65 gives up 11.9 points of fire at n = 2.417, worth −2.38, and tilt another −1.15. Brilliance of +1.50 and scintillation of +1.31 cannot cover it.
TermThis cut / standardPoints
Brillianceweight 0.3496.792.3+1.50
Fireweight 0.2066.978.8−2.38
Tiltweight 0.1683.290.4−1.15
Scintillationweight 0.1084.971.8+1.31
Symmetryweight 0.10100.0100.0+0.00
Leakweight 0.10 ↓2.571.88−0.07
Sum of the six terms−0.79
Published Global gap −0.82. The six terms reconstruct it to
0.03 of a point. The difference is rounding in the source figures, not a second method.
In moissanite n = 2.65
Ahead
95.13 against the standard's 89.82. The largest margin in the registry and the most honest one: only +1.31 of the +5.31 is facet count. Brilliance alone is +4.35, at 98.1 against the standard’s 85.3.
TermThis cut / standardPoints
Brillianceweight 0.3498.185.3+4.35
Fireweight 0.2099.697.5+0.42
Tiltweight 0.1684.393.2−1.42
Scintillationweight 0.1084.971.8+1.31
Symmetryweight 0.10100.0100.0+0.00
Leakweight 0.10 ↓1.057.76+0.67
Sum of the six terms+5.33
Published Global gap +5.31. 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
Behind
87.12 against the standard's 91.77. The gradient reversal in full: at n = 2.16 the same pavilion leaks 8.68%, seventeen times the standard's 0.51%, and brilliance and fire give back −5.05 between them.
TermThis cut / standardPoints
Brillianceweight 0.3491.198.0−2.35
Fireweight 0.2073.386.8−2.70
Tiltweight 0.1686.787.1−0.06
Scintillationweight 0.1084.971.8+1.31
Symmetryweight 0.10100.0100.0+0.00
Leakweight 0.10 ↓8.680.51−0.82
Sum of the six terms−4.62
Published Global gap −4.65. The six terms reconstruct it to
0.03 of a point. The difference is rounding in the source figures, not a second method.
Against the control
How much of this is facet count
Global gives scintillation a tenth of its weight, and scintillation is a closed formula on facet count rather than a ray measurement. At 85 facets M5 banks less of that term than any other house cut, and it needs it least. Measured here in moissanite, the material it was drawn for.
The facet-count term
Of the +5.31 moissanite margin, only +1.31 is scintillation, a formula on 85 facets rather than a measurement. The optical margin, the part traced ray by ray, is +4.00, the largest figure in the registry in any material.
Against BL-Vitruvio
Vitruvio carries Tolkowsky’s own angles at 185 facets, so it is the fair control for a finely cut modern stone. In moissanite M5 finishes +2.27 above it on Global and +3.62 on the optical terms alone, while conceding a hundred facets on the scintillation term.
What the angles buy
Put M5’s angles on a plain 57-facet pavilion, crown 32.0°, pavilion 41.25°, table 56.0%: brilliance +2.9 over the standard, fire unchanged, tilt −4.6, leak 1.6 points lower. On their own the angles are worth very little.
What the tiling buys
The 85-facet pavilion is the cut: brilliance +8.4, leak 4.7 points lower and fire +2.5, costing 2.0 of tilt. Re-aim M5 to 1919 angles on its own pavilion and it gives up only 0.24 of Global. Almost everything here is the facet pattern rather than the angles.
Where it departs from 1919
A different material, and only then a different angle
M5’s pavilion sits at 41.25° and its crown at 32.00°, half a degree and two and a half degrees off Tolkowsky. His figures are for diamond at n 2.417. This cut is drawn for moissanite at 2.65, and the refractive index is the first thing that moves the answer.
Pavilion: +0.50°
Swept on its own 85-facet pavilion in moissanite, the optimum is 41.50° with a plateau from 41.25°. M5 is built at 41.25°, 0.05 of a point off the best value the sweep can find. It is sitting on its plateau.
The optimum is not portable
Sweep the same angle on the standard’s plain 57-facet pavilion in moissanite and the answer is 38.25°. Put 38.25° on M5’s pavilion instead and it leaks 28.9% and scores 83.13. The best angle belongs to a material and a layout together, never to a material on its own.
Crown: −2.51°
Shallower than his, as with the other house cuts, and for the same reason: on this engine Global holds its value across 2.5° of crown but only 0.75° of pavilion. The crown is the parameter with room in it.
What it costs elsewhere
The same geometry finishes 0.82 behind the standard in diamond and 4.65 behind in cubic zirconia. That is not a fault in the cut, it is the specialisation being honest. Sweeps run at four times the standard ray count.
What it’s doing
There is a clean test for whether a cut is genuinely index-specific or only labelled that way: watch what leakage does as refractive index rises. Every diamond-tuned cut in the registry leaks more the higher the index goes. The standard runs 0.51% in cubic zirconia, 1.88% in diamond and 7.76% in moissanite, and every one of the eight other cuts follows the same gradient.
BL-M5 runs the other way: 8.68%, 2.57%, 1.05%. It is the only cut here that does, and it is why its moissanite result is the most honest margin in the registry. Of its +5.31, only +1.31 is facet count. Brilliance alone is +4.35, at 98.1 against the standard’s 85.3.
Where it gives ground
Everything that is not moissanite. It sits 0.82 below the standard in diamond, the only deficit in that column, and 4.65 below in cubic zirconia, the largest deficit in the registry. In diamond it is also the least steady cut under tilt (83.2) and carries the lowest fire figure in the registry (66.9).
Read that as the design working exactly as intended, in the wrong material.
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.
The rest of the registry
Ahead of the standard in moissanite. Behind it in diamond and cubic zirconia.