CUT: the angles and proportions of diamonds. 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. Diamonds that are cut too deep or too shallow lose or leak light through the side or bottom, resulting in less brilliance and ultimately, value. Cut also refers to shape—round, square, pear, or heart etc. Since a round diamond is symmetrical and capable of reflecting nearly all the light that enters, it is the most brilliant of all diamond shapes and follows specific proportional guidelines.