The GIA Cut Scale ranges from Excellent to Poor and they provide a cut quality grade for standard round brilliant diamonds that fall in the D to Z color range. A polished diamond's beauty lies in its complex relationship with light:
- how light strikes the surface
- how much enters the diamond
- how light returns to the eye
- in what form light returns to the eye
The result of the complex relationship with light is a magnificent display of three attributes. Brightness is the combination of all white light reflecting from the surface and interior of a diamond. Fire describes the "flares" of color emitted from a diamond. Scintillation describes the flashes of light you see when the diamond, the light or when the observer moves.
A polished diamond's proportions affect its light performance, which in turn affects its beauty and overall appeal. Diamonds with fine proportions, symmetry and polish optimize their interaction with light, and have increased brightness, fire and scintillation.