Next up in GIA’s 4Cs Q&A series is diamond cut grading.
A: The distance from the bottom edge of the girdle to the culet is the pavilion depth. A pavilion depth that’s too shallow or too deep will allow light to escape from the side of the stone and or leak out of the bottom. A well-cut diamond will direct more light through the crown.
Q: Why doesn’t GIA offer a cut grade for fancy-shape diamonds?
A: Establishing quality parameters for fancy-shape diamond cuts is extremely complex–much more so than for round diamonds because of the greater variations in shape–and measuring technology needs to progress far enough to capture the features considered important for fancy shapes. GIA is committed to developing a system that is accurate, comprehensive, and practical.
Q: How is diamond cut evaluated for standard round brilliant diamonds?
A: GIA uses sophisticated optical measuring devices to capture the measurements of those facets that influence the diamond’s face-up appearance. A diamond’s cut grade is established by comparing these measurements against a database of more than 38.5 million proportion sets of known grades and by the visual observations of polish and symmetry by GIA expert graders.
Updated: GIA report scales have been updated with the newest scales as of May 2014