The Modern Cut Grade System (5.43)
The final cut grade system includes the maximum amount of brilliance in the round brilliant's face-up position which is made up of the following:
Brightness: The return of white light.
Fire: The color flashes originating from the dispersion, (spectral colors caused by refraction or bending of white light.
Scintillation: The spectral colors come alive with the movement of the diamond causing the many infinite reflection directions, in which some would call sparkle.
Polish: Crucial in reflecting the light to optimize the excellent cut grade.
Symmetry: Obvious symmetry issues such as a table that is out of center will definitely affect the viewer's observation of brilliance. Minor symmetry issues such the midpoints on the crown and pavilion mains are slightly off are not going to have any impact on the overall brilliance to the human observer with the naked eye.
Durability: A very thin or extremely thin girdle may not affect the overall brilliance but it may cause chipping.