The Round, or Brilliant Cut Diamond is, by far, the most popular shape for diamond engagement rings. It is cone-shaped to maximize light return through the top of the diamond. It is cut to have 58 facets—33 on the crown and 25 on the pavilion. Any facets cut on the girdle do not count. The relationship between the angle of the crown (above the girdle) and the pavilion (below the girdle) is complementary. A steep crown angle is complemented by a shallower pavilion angle, and vice versa. This relationship was honed over the last hundred years, when diamond cutter began using advanced theories of light behavior and mathematical calculations that would most increase to brilliance, or light return, in a diamond. It is because of these advances in diamond technology that diamond cutters were able to create the shape that would most make it seem as though light passing through it was ‘dancing`. Brilliant cut diamonds should not be too shallow or too wide, as the light reflecting back through it will be lessened, and it will appear darker. According to Tolkowsky`s specifications, the cut height should be 59.3% of the diameter of the diamond, with about 43% for the pavilion and 16% for the crown. Tolkowsky, a Russian mathematician, in his PhD thesis, considered such advanced variables as index of refraction and covalent bond angles to describe what has simply become known as the “Brilliant Cut�. A lot of time, energy, and thinking went into creating the ideal diamond shape. Some of the more famous Round Cut diamond engagement rings were given to women ranging from Angie Harmon to Barbra Streisand to Christina Aguilera. The Round, or Brilliant, Cut is considered the “classic� diamond shape for engagement rings.