Cut & Shape
Cut is often confused with shape. Shape refers to the overall outline of a diamond when viewed from the top. Examples include princess, emerald, marquise, oval, pear, heart and cushion. These are usually referred to as “fancy” shapes.

The overwhelming majority of diamonds, however, are round, and the most common cut is the round brilliant. A diamond’s cut grade refers to the placement and proportions of facets in a round-brilliant diamond, measuring the extent to which they maximize brilliance (light return), scintillation (sparkle) and fire (flashes of color).

There is no one single set of angles and proportions that constitute an ideal round-brilliant cut, but there are general parameters that dictate the quality of a diamond’s cut. Width and depth affect how light travels through a diamond and where it exits a diamond. The goal is to angle the facets in a way that causes them to refract light out through the top, or table, of a diamond. When a diamond is too shallow, light will exit through the bottom or pavilion. When a diamond is too deep, light will exit through the sides of the pavilion.

Polish and symmetry also affect the beauty of a diamond. Polish refers to the smoothness of the diamond’s facets. Symmetry refers to the alignment of the facets. Even with a good cut, poor symmetry can redirect light return, causing it to exit through the pavilion instead of the table. A poor polish can make a diamond appear dull and lifeless.

Most larger diamonds are accompanied by a certificate that grades and describes a diamond’s cut, including separate grades for polish and symmetry.

Why aren’t all diamonds cut to ideal proportions?
To cut a diamond perfectly, a craftsman will often need to cut away more than 50% of the rough diamond, so there is usually a tradeoff between ideal cut and weight retention – the primary determinant of a diamond’s value.