4.44 points ahead of the 1919 ideal in diamond, and the most fire of any cut measured here.
Global score against T57, Tolkowsky’s 1919 ideal, measured the same way in the same material.
Diamondn = 2.417+4.44Ahead
Moissaniten = 2.65+1.80Ahead
Cubic zirconian = 2.16+3.24Ahead
−6T57 = 0+6
The short version
Girandola is the most single-minded of the house diamond cuts. It carries 85.4 points of fire against the standard’s 78.8, the highest diamond figure in the registry.
Of its +4.44 margin, +2.68 is scintillation and +1.32 is fire, which is the term it was designed around. It pays in leak: 4.42% against 1.88%, worth −0.25. If you want coloured flash rather than white brightness, that is the trade, made deliberately, and on the record.
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
93.05 against the standard's 88.61. Scintillation is +2.68 of it, facet count doing what facet count does. Fire is the real work at +1.32, the largest fire contribution in the registry, paid for with −0.25 of leak.
TermThis cut / standardPoints
Useful lightweight 0.3493.192.3+0.27
Fireweight 0.2085.478.8+1.32
Tiltweight 0.1693.190.4+0.43
Scintillationweight 0.1098.671.8+2.68
Symmetryweight 0.10100.0100.0+0.00
Leakweight 0.10 ↓4.421.88−0.25
Sum of the six terms+4.45
Published Global gap +4.44. 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
91.62 against the standard's 89.82. The whole margin is scintillation: +2.68 against a +1.80 result, because brightness and fire both go backwards, at −0.44 and −0.90. 84.0% useful light is the lowest figure anywhere in the registry.
TermThis cut / standardPoints
Useful lightweight 0.3484.085.3−0.44
Fireweight 0.2093.097.5−0.90
Tiltweight 0.1696.293.2+0.48
Scintillationweight 0.1098.671.8+2.68
Symmetryweight 0.10100.0100.0+0.00
Leakweight 0.10 ↓7.907.76−0.01
Sum of the six terms+1.80
Published Global gap +1.80. The six terms reconstruct it exactly.
In cubic zirconia n = 2.16
Ahead
95.01 against the standard's 91.77. Fire lifts again at +0.96, and 91.6 tops the zirconia column, while tilt hands back −0.30 at 85.2, the lowest tilt figure in that column.
TermThis cut / standardPoints
Useful lightweight 0.3497.898.0−0.07
Fireweight 0.2091.686.8+0.96
Tiltweight 0.1685.287.1−0.30
Scintillationweight 0.1098.671.8+2.68
Symmetryweight 0.10100.0100.0+0.00
Leakweight 0.10 ↓0.510.51+0.00
Sum of the six terms+3.27
Published Global gap +3.24. 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
The ledger is unusually lopsided. Brightness barely moves, at +0.27. What Girandola does is take dispersion up 6.6 points, worth +1.32, the largest fire contribution in the registry, and accept the consequence: light that travels further inside the stone before it returns is light that more often does not return at all.
Two and a half points of extra leakage cost it −0.25. Set against the +2.68 it banks on facet count, the fire is the part of this cut that is actually designed, and it is the part worth paying for.
Where it gives ground
Leak, and moissanite. At 4.42% it holds less light than the standard, than Miliano, or than either of the shorter T-series references.
And the geometry that buys fire in diamond stops buying it at n = 2.65: in moissanite Girandola returns less fire than the standard does, 93.0 against 97.5, worth −0.90. Its +1.80 there is the weakest showing of the three house diamond cuts, and every point of it comes from facet count. The trade only works in the material it was drawn for.
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.