Diamond cut constitutes the more or less symmetrical arrangement of facets which together help define appearance of a diamond. In this manner, it is a style or design guide used when shaping a diamond for polishing. Cut does not refer to shape like pear or oval, but the symmetry, proportioning, and polish of the diamond itself.
In order to best utilize a diamond gemstone's material properties, a number of different cuts
have been created. The most popular of diamond cuts is the modern Round Brilliant, whose facet arrangements and proportions have been perfected by both mathematical and empirical analysis. Round diamonds are symmetrical and capable of reflecting nearly all the light that enters, so it is the most brilliant of all diamond shapes and follows specific proportional guidelines. Non-round shapes, also known as “fancy shapes”, must also follow guidelines in order to be considered well cut. The prevalence and choice of a particular fancy cut is also influenced by fashion.
Cut the only quality that is affected by human effort. It requires great skill, training and experience to be an expert craftsman. Diamond cutters must consider several factors, such as the shape and size of the crystal, location of internal flaws or “inclusions,” when choosing a cut. The cutter polishes small surfaces known as facets onto the rough diamond. This process creates the facets known as the crown, table, girdle, pavilion and culet of the diamond.
A well-cut diamond will internally reproduce light from one mirror-like facet to another and dissolve and reflect it through the top of the gem. The facets, when arranged in precise proportions, will maximize the fire life and brilliance of a diamond. A well-cut diamond will be higher in quality and value than deep or shallow-cut diamonds. Diamonds that are cut too deep or too shallow lose or leak light through the side or bottom, resulting in less brilliance and a less valuable stone. To cut a diamond perfectly, a craftsman usually needs to cut more than half of the rough diamond.