A well-cut diamond will internally reflect light from one mirror-like facet to another and disperse and reflect it through the top of the stone. This is based on a scientific formula and results in a varied display of brilliance and fire. Diamonds that are cut too deep or too shallow lose or “leak” light through the sides or bottom, resulting in less brilliance and, as a result, lower value.

Cut also refers to shape—round, square, pear, or emerald for example. A round diamond is symmetrical and therefore reflects almost all of the light that enters it. The round cut is the most brilliant of all diamond shapes and follows specific proportional guidelines. Non-round shapes are also known as “fancy shapes” — these have their own guidelines to determine quality of cut.