DigitalGemology/cut-performance-index

Digital Gemology Cut Performance Index

Ray-traced light-performance scores (brilliance, fire, scintillation, tilt, symmetry, spread, shape-norm, leakage, overall) for 40 gem cuts and 5 Platonic solids in seven gemstones: diamond, moissanite, cubic zirconia, ruby, sapphire, emerald and amethyst. Computed by Digital Gemology's light-census ray tracer from each cut's facet geometry.

• Source and live page: https://digitalgemology.com/learn/cut-performance-index
• Same data as JSON: https://digitalgemology.com/data/cut-performance-index.json and through the API at https://digitalgemology.com/api/cut-index
• Version: 2026-10-31 (census-ba47e2e1.13d5809b)
• License: CC BY 4.0. Use and share freely, with credit to Digital Gemology and a link to https://digitalgemology.com/learn/cut-performance-index.
• Also on Kaggle: https://www.kaggle.com/datasets/digitalgemology/digital-gemology-cut-performance-index
• Also on Hugging Face: https://huggingface.co/datasets/DigitalGemology/cut-performance-index
• DOI (Zenodo, all versions): 10.5281/zenodo.23844870

Contents

cut-performance-index.csv and cut-performance-index.json hold the same 315 rows: 45 cuts × 7 materials. 37 cuts are scored in each material; the others are listed as "not yet scored" with the reason. Figures are unrounded; the live page shows one decimal.

Top five overall:

• Diamond: DG-Miliano (92.7), DG-Rafaello (92.6), DG-Vitruvio (91.7), T105 Round Brilliant (90.6), DG-Broken Hearts and Arrows (90.4)
• Moissanite: DG-M5 (95.1), DG-Vitruvio (92.9), DG-Miliano (92.0), Portuguese Bird's Nest (91.8), DG-Broken Hearts and Arrows (91.7)
• Cubic Zirconia: DG-Rafaello (95.0), DG-Miliano (94.9), DG-Vitruvio (94.6), T105 Round Brilliant (93.3), DG-Broken Hearts and Arrows (93.2)
• Ruby: DG-M5 (82.3), DG-Anteros (81.7), DG-Vitruvio (80.7), DG-Miliano (79.6), DG-Broken Hearts and Arrows (79.6)
• Sapphire: DG-M5 (82.3), DG-Anteros (81.7), DG-Vitruvio (80.7), DG-Miliano (79.6), DG-Broken Hearts and Arrows (79.6)
• Emerald: DG-M5 (77.7), DG-Anteros (77.3), DG-Vitruvio (74.4), DG-Broken Hearts and Arrows (73.2), T73 Round Brilliant (72.6)
• Amethyst: DG-M5 (75.8), DG-Anteros (75.7), DG-Vitruvio (71.4), DG-Broken Hearts and Arrows (69.8), T73 Round Brilliant (69.6)

Highest overall score in each family:

• Brilliants — diamond: DG-Vitruvio (91.7); moissanite: DG-Vitruvio (92.9); cubic zirconia: DG-Vitruvio (94.6); ruby: DG-Anteros (81.7); sapphire: DG-Anteros (81.7); emerald: DG-Anteros (77.3); amethyst: DG-Anteros (75.7)
• Jewelry cuts — diamond: Portuguese Bird's Nest (86.4); moissanite: Portuguese Bird's Nest (91.8); cubic zirconia: Portuguese Bird's Nest (88.4); ruby: Trillion (76.3); sapphire: Trillion (76.3); emerald: Trillion (70.2); amethyst: Trillion (68.3)
• Historic cuts — diamond: T57 Round Brilliant (88.6); moissanite: T57 Round Brilliant (89.8); cubic zirconia: T57 Round Brilliant (91.8); ruby: T57 Round Brilliant (78.1); sapphire: T57 Round Brilliant (78.1); emerald: T57 Round Brilliant (71.7); amethyst: T57 Round Brilliant (68.6)
• House cuts — diamond: DG-Miliano (92.7); moissanite: DG-M5 (95.1); cubic zirconia: DG-Rafaello (95.0); ruby: DG-M5 (82.3); sapphire: DG-M5 (82.3); emerald: DG-M5 (77.7); amethyst: DG-M5 (75.8)

Cuts covered

• Brilliants: T73 Round Brilliant, T105 Round Brilliant, DG-Vitruvio, DG-Anteros, DG-Broken Hearts and Arrows
• Jewelry cuts: Asscher, Baguette, Cushion, Emerald Cut, Emerald Square, Heart, Hexagon, Marquise, Octagon, Oval, Pear, Portuguese Bird's Nest, Princess, Radiant, Radiant Square, Rectangle, Square, Teardrop, Triangle, Trilliant, Trillion
• Historic cuts: Old Single, Mazarin, Peruzzi, Old Mine, Old European, T57 Round Brilliant
• House cuts: DG-Bowtie, DG-Cabochon, DG-Elongated Hexagon, DG-M5, DG-Miliano, DG-Octagonal Kite, DG-Rafaello, Elongated Hexagonal Bipyramid
• Platonic solids: Dodecahedron, Hexahedron, Icosahedron, Octahedron, Tetrahedron

Each cut's page on digitalgemology.com sells its 3D model files (STEP, 3DM, STL, OBJ, FBX, GLB), and most also sell a GemCad faceting diagram. The free gemstone simulator on the site shows the cuts in diamond, moissanite, cubic zirconia, ruby, sapphire, emerald and amethyst.

Columns

All scores are out of 100 except leakage (per cent, lower is better). Spread and shape-norm can be above 100. Scintillation, symmetry and spread depend only on the shape, so they are the same in every stone.

Column	Meaning
slug	Cut identifier, as in the cut's URL.
name	Cut name.
category	Cut family on the site (Brilliants, Jewelry cuts, Historic cuts, House cuts, Platonic solids).
material	diamond (refractive index 2.417), moissanite (2.65), cubic-zirconia (2.16), ruby and sapphire (1.765, corundum: the same figures), emerald (1.578) or amethyst (1.548). Never compare or rank across materials.
status	'scored', or 'not yet scored' (then the scores are empty and reason says why).
rank	Place within the material by the overall score shown to one decimal; equal shown figures share a place.
overall	The combined score: 0.34 × brilliance + 0.20 × fire + 0.16 × tilt + 0.10 × scintillation + 0.10 × symmetry + 0.10 × (100 − leakage).
brilliance	The share of the light that enters the stone and comes back out of the crown towards the viewer, in per cent.
fire	The share of that returned light whose colors spread apart by more than 0.6° as it leaves, in per cent. It does not say how much light returns.
scintillation	A sparkle score from the number of facets the stone really shows: 100 × (1 − e^(−facets / 45)). It depends only on the geometry.
tilt	How much of its face-up brilliance the stone keeps when tilted 20°, capped at 100.
symmetry	How evenly the pavilion facets of each design family are cut: 100 − 6 × their scatter in degrees.
spread	Face-up size for the weight compared with a stone 61.5% deep: 100 × ∛(61.5 / depth %), capped at 130. Above 100 means larger than that stone.
shape_norm	Brilliance compared with what the shape family can reach (93 for round brilliants, 86 for fancy brilliants, 76 for step cuts, 64 for others), capped at 125.
leakage	The share of the light that enters and leaks out, through the pavilion or through the crown heading down, in per cent. Lower is better.
geometry	Which facet set was traced (the census plane set, or our own 3D model).
reason	Why a cut is not scored yet; empty for scored cuts.
url	The cut's page on digitalgemology.com.
engine_version	Version of the scoring code; it changes whenever that code changes.
generated	Date the figures were last changed.

Method

Each cut is a set of flat facets that close into a convex solid, scaled so that its longest side is 1, table up. 3,200 rays fall on the stone from above, at most about 7° from vertical (cosine-weighted), over the whole face-up outline, with a fixed random seed, so every run gives the same scores. At each surface a ray refracts by Snell's law or reflects totally beyond the critical angle, for up to 12 reflections inside the stone.

A ray counts as returned when it leaves through the crown within 64° of vertical after at least one reflection inside the pavilion; a ray that leaves through the pavilion, or through the crown heading down, counts as leakage. For fire, the exit is traced again at the refractive index minus and plus the dispersion; when the two directions differ by more than 0.6°, the returned ray counts as fire. Tilt reruns the trace with the stone turned 20° about its long axis (2,200 rays).

Each stone is traced with its own refractive index and dispersion. Ruby and sapphire are both corundum, so they share one index and one set of figures. For colored stones the scores compare cuts within that stone: the trace does not absorb light, so a dark stone looks darker than its score.

The trace is all or nothing: no Fresnel splitting, and no absorption, color, inclusions or polish. The light cone, viewing limit, fire threshold, weights and constants are fixed settings of the method, the same for every cut, so the scores compare cuts with each other; they are not absolute measures. Full method: https://digitalgemology.com/learn/cut-performance-index

Citation

Digital Gemology (2026). Digital Gemology Cut Performance Index, version 2026-10-31 (engine census-ba47e2e1.13d5809b). https://digitalgemology.com/learn/cut-performance-index