In our models, a round brilliant returns far more light; an oval looks larger and scores higher for fire. In our ray traces of diamond, the round brilliant scores 93 for brilliance, the oval 47. The oval scores 92 for fire against 78, and 87 for scintillation against 80. Its face-up area is 8% larger for the same weight. But it leaks 27% of the light, the round brilliant 2%.
| Shape | Brilliance | Fire | Scintillation |
|---|---|---|---|
| Round brilliant | 93 | 78 | 80 |
| Oval | 47 | 92 | 87 |
Why
The oval is a round brilliant stretched into an ellipse. Its pavilion facets slope at different angles along the length and across the width. Where the angles are wrong for the stone, light passes out of the back instead of returning. In an oval, this leakage can show as a dark bow-tie across the center. Your head, reflected in the stone, can make one too.
The longer outline spreads the same weight over a larger area, so the oval faces up larger.
Compare any two cuts in the Cut Performance Wheel, or turn them in light in the 3D Gemstone Simulator.