House cut · 85 facets · Registry 21 July 2026

BL-M5

Solved for moissanite.

The only cut in the registry that beats the 1919 ideal in moissanite, by 2.27 points.

Global score against Tolkowsky 1919, measured the same way in the same material.

Diamondn = 2.417 −3.86 Behind
Moissaniten = 2.65 +2.27 Ahead
Cubic zirconian = 2.16 −7.47 Behind

−8Tolkowsky 1919 = 0+8

The short version

BL-M5 is a single-material design and doesn't pretend otherwise. In moissanite it returns 98.1% of light usefully against the standard's 86.1%, and loses 1.05% to leakage against 7.46%. That is a sevenfold reduction in wasted light, and it carries the cut 2.27 points clear of Tolkowsky.

In diamond and cubic zirconia it is the weakest cut in the registry. 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 91.65. The single-cone pavilion aimed at n = 2.65 gives up 11.8 points of fire at n = 2.417, worth −2.36. Brightness stays high, at 96.7, worth +1.39, and cannot cover the fire, tilt and scintillation losses.

TermThis cut / standardPoints
Useful lightweight 0.34 96.792.6 +1.39
Fireweight 0.20 66.978.7 −2.36
Tiltweight 0.16 83.292.5 −1.49
Scintillationweight 0.10 84.998.4 −1.35
Symmetryweight 0.10 100.0100.0 +0.00
Leakweight 0.10 ↓ 2.572.17 −0.04
Sum of the six terms −3.84

Published Global gap −3.86. 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 95.13 against the standard's 92.86. +4.08 from brightness and +0.64 from retained light, against −1.55 tilt and −1.35 scintillation. The largest single-term swing anywhere in the registry.

TermThis cut / standardPoints
Useful lightweight 0.34 98.186.1 +4.08
Fireweight 0.20 99.697.2 +0.48
Tiltweight 0.16 84.394.0 −1.55
Scintillationweight 0.10 84.998.4 −1.35
Symmetryweight 0.10 100.0100.0 +0.00
Leakweight 0.10 ↓ 1.057.46 +0.64
Sum of the six terms +2.30

Published Global gap +2.27. The six terms reconstruct it to 0.03 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 94.59. The gradient reversal in full: at n = 2.16 the same pavilion leaks 8.68%, fifteen times the standard's 0.58%.

TermThis cut / standardPoints
Useful lightweight 0.34 91.198.4 −2.48
Fireweight 0.20 73.387.0 −2.74
Tiltweight 0.16 86.787.1 −0.06
Scintillationweight 0.10 84.998.4 −1.35
Symmetryweight 0.10 100.0100.0 +0.00
Leakweight 0.10 ↓ 8.680.58 −0.81
Sum of the six terms −7.45

Published Global gap −7.47. The six terms reconstruct it to 0.02 of a point. The difference is rounding in the source figures, not a second method.

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 0.58% in cubic zirconia, 2.17% in diamond, 7.46% in moissanite, and six of the seven other cuts follow the same gradient.

BL-M5 runs the other way: 8.68%, 2.57%, 1.05%. It is the only cut in the registry with that gradient reversed. That is what a pavilion solved for n = 2.65, rather than adapted to it, looks like in the data.

The bill arrives in two lines. At 85 facets, scintillation reads 84.9 against the standard's 98.4, costing 1.35. Tilt reads 84.3 against 94.0, costing 1.55. M5 buys 4.08 points of brightness, 0.64 of retained light and 0.48 of fire, 5.20 in all, and hands 2.90 of it back in sparkle density and off-axis stability. It still finishes 2.27 ahead.

Where it gives ground

Everything that is not moissanite. It sits 3.86 points below the standard in diamond and 7.47 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.

The formula

Global = 0.34 useful + 0.20 fire + 0.16 tilt + 0.10 scintillation + 0.10 symmetry + 0.10 (100 − leak).

What we won't claim

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.

The rest of the registry

Ahead of the standard in moissanite.

House cut · 201 facets BL-Miliano Ahead +1.80 in diamond House cut · 193 facets BL-Cinderella Ahead +1.40 in diamond House cut · 193 facets BL-Rafaello Ahead +1.19 in diamond Standard · 185 facets Tolkowsky 1919 Level +0.00 in diamond Reference · 73 facets Tolkowsky 73 Behind −1.80 in diamond Reference · 73 facets Brilliant 73 Behind −2.13 in diamond Reference · 57 facets Tolkowsky 57 Behind −2.82 in cubic zirconia