Considered the most important of the 5Cs, diamond cut refers to two important aspects of the diamond. First, "cut" is used to describe the shape of the diamond, whether it's round, princess, radiant, marquise or any of the other commonly seen shapes.
The second usage is how the diamond is physically cut. This "cut" gives the diamond its brilliance and sparkle – how light is reflected, dispersed and scintillated. Unlike color and clarity, there is not a single grade that defines it. Furthermore, two diamonds equal in carat weight, color and clarity can differ in appearance and value because of differences in cut quality.
The cut is the most complicated of the 5Cs. Unlike carat weight, color and clarity, whose value and rarity are related to the diamond's natural formation, cut quality is the result of human decision and diamond cutting skills.
There are three factors that determine a diamond's cut quality:
- Proportions: the relative sizes and angles of the diamond's parts and facets
- Symmetry: the precision of the cut design, especially the facets
- Polish: the smoothness and luster of the diamond's surface
Cut grades are referenced on a diamond's certificate often using the GIA standards of Excellent, Very Good, Good, Fair and Poor. The quality of a diamond's cut always speaks for itself.