Learn how physics and math are used to maximize the brilliance and fire of a cut diamond, in this video from NOVA: Treasures of the Earth: Gems. In 1919, a mathematician used principles of optical physics to determine the optimum number and angle of facets to create a diamond that best caught the light and reflected it out through the top of the gemstone. A demonstration shows how light travels through a rounded crystal but reflects off the internal surfaces of a faceted crystal. Animations illustrate how white light reflects within a faceted diamond and how dispersion creates flashes of color (called fire). This resource is part of the NOVA Collection.