Diamond Cut
The single most important factor in a diamond's beauty.
Of all the 4Cs, cut has the greatest influence on a diamond's sparkle. A well-cut diamond reflects light internally from one facet to another, then disperses it through the top of the stone in a dazzling display of brilliance and fire. Even a diamond with perfect color and clarity will look dull if it is poorly cut.
Cut should not be confused with shape (round, oval, princess, etc.). Cut refers specifically to how well a diamond's facets interact with light, and it depends on three measurable optical properties:
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Brilliance
White light reflected from the surface and interior of the diamond. A well-cut stone appears bright and lively.
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Fire
The dispersion of white light into spectral colors — the flashes of red, blue, and orange you see when the diamond moves.
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Scintillation
The pattern of light and dark areas and the flashes of sparkle when the diamond, light source, or observer moves.
How Cut Is Graded
The GIA grades round brilliant diamonds on a five-point scale from Excellent to Poor. The grade is determined by evaluating proportions (table size, crown angle, pavilion depth, girdle thickness) and their combined effect on light performance.
GIA Cut Grade Scale
| Grade | Light Performance | Recommendation |
|---|
| Excellent | Maximum brilliance, fire, and scintillation. Light entering the diamond is almost entirely reflected through the top. | The ideal choice — delivers the most stunning visual impact. |
| Very Good | Nearly as much brilliance as Excellent. Slight deviations in proportions are virtually undetectable. | Outstanding value — very difficult to distinguish from Excellent in person. |
| Good | Reflects most light that enters. Some brilliance is lost due to slightly off-ideal proportions. | A solid budget-conscious choice. Still attractive to the eye. |
| Fair | Noticeably less brilliant. Light escapes through the bottom or sides of the stone. | May appear glassy or dark in areas. Consider upgrading if budget allows. |
| Poor | Most light is lost. The diamond appears lifeless and lacks sparkle. | Not recommended. Significant visual impact on beauty. |
Key Proportions That Affect Cut
Every diamond is measured for specific proportions that determine how light travels through the stone. The most critical measurements are:
- Table Percentage — The width of the top facet relative to the diamond's diameter. Too large = less fire; too small = less brilliance. Ideal for round: 54–57%.
- Crown Angle — The angle between the girdle and the table. Controls the balance between brilliance and fire. Ideal: 34–35°.
- Pavilion Depth — The distance from the girdle to the culet. If too deep, light leaks out the bottom; if too shallow, light passes straight through. Ideal: 42.8–43.2%.
- Girdle Thickness — A very thin girdle risks chipping; a very thick girdle adds hidden weight without visual size. Ideal: thin to slightly thick.
Shallow vs. Ideal vs. Deep
Too Shallow
Light enters the crown and leaks out the bottom. The diamond appears watery and lifeless. May look larger face-up but sacrifices brilliance.
Ideal Cut
Light enters the crown, bounces between pavilion facets, and exits through the top as brilliance and fire. Maximum light return.
Too Deep
Light hits the pavilion at too steep an angle and escapes out the sides. The diamond appears dark in the center and smaller than its carat weight.
Our Recommendation
We recommend prioritizing cut above all other Cs. A smaller diamond with an Excellent cut will outshine a larger diamond with a Fair cut every time. For engagement rings and diamond solitaire pendants where a single stone is the focal point, Excellent or Very Good cut is especially important.
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