Diamonds are renowned for their ability to sparkle and transmit light. We often think that diamond ‘cut’ is referring to the overall shape of the stone (round, emerald, princess, etc.), but a diamond’s cut grade is really referring to how well a diamond is faceted and how those facets interact with light.
Precise artistry and workmanship are required to fashion a stone so its proportions, symmetry, and polish deliver the magnificent return of light only possible in a diamond.
For example, to determine the cut grade of a traditional round brilliant diamond - the shape that dominates the majority of diamond jewelry - GIA calculates the proportions of those facets that influence the diamond’s face-up appearance. These proportions allow GIA to evaluate how successfully a diamond interacts with light to create desirable visual effects such as:
Brightness: Internal and external white light reflected from a diamond
Dispersion (Fire): The scattering of white light into all the colors of the rainbow
Scintillation: The amount of sparkle a diamond produces, and the pattern of light and dark areas caused by reflections within the gem.
GIA’s diamond cut grade also takes into account the design and craftsmanship of the diamond. This includes its weight relative to its diameter, girdle thickness (which affects its durability), symmetry of its facet arrangement, and the quality of polish on those facets.
The GIA Diamond Cut Scale for standard round brilliant diamonds contains five grades ranging from Excellent to Poor.