Brightness, fire, and scintillation — maximizing optical performance.
Diamond cut grade evaluates how effectively a diamond interacts with light. Unlike the other Cs, cut is not a natural characteristic but a human-crafted one. The precision of a diamond's cut determines its brilliance, fire, and scintillation the three components that give a diamond its captivating beauty.
BGI's cut grading within the 6C system applies to round brilliant diamonds, the most common and scientifically studied shape. Our evaluation encompasses both the objective optical performance and the craftsmanship of facet placement and symmetry.
BGI evaluates three optical components when grading cut: Brightness is the total white light reflected from the diamond's crown and pavilion. Fire refers to the dispersion of white light into spectral colors as it passes through the diamond. Scintillation is the pattern of light and dark areas that flash as the diamond moves.
A well-cut diamond optimizes all three components through precise angle relationships between the crown, pavilion, and girdle. Even a diamond with perfect color and clarity will appear lifeless if poorly cut.
Cut is widely considered the most important of the 4Cs because it directly controls a diamond's beauty. An Excellent-cut diamond can appear more brilliant than a higher-clarity diamond with a Good cut. BGI's cut grading ensures that every certificate reflects the true optical performance of the stone.
| Grade | Description |
|---|---|
| Excellent | Outstanding brightness and fire. Optimal proportions for maximum light return. |
| Very Good | Superior brilliance with only minor deviations from optimal proportions. |
| Good | Strong brightness with satisfactory proportions. Good value option. |
| Fair | Acceptable brilliance with noticeable proportion issues. Light leakage possible. |
| Poor | Visible light leakage. Suboptimal proportions significantly reduce beauty. |
Last Updated: June 2026 · BGI 6C Diamond Standards™