A diamond cut is a style or design guide used when shaping a diamond for polishing such as the brilliant cut. Cut does not refer to shape (pear, oval), but the symmetry, proportioning and polish of a diamond. The cut of a diamond greatly affects a diamond's brilliance — a poorly-cut diamond is less luminous. In order to best use a diamond gemstone's material properties, a number of different diamond cuts have been developed. A diamond cut constitutes a more or less symmetrical arrangement of facets, which together modify the shape and appearance of a diamond crystal. Diamond cutters must consider several factors, such as the shape and size of the crystal, when choosing a cut. The practical history of diamond cuts can be traced back to the Middle Ages, while their theoretical basis was not developed until the turn of the 20th century. Design, creation and innovation continue to the present day: new technology—notably laser cutting and computer-aided design—has enabled the development of cuts whose complexity, optical performance, and waste reduction were hitherto unthinkable. The most popular of diamond cuts is the modern round brilliant, whose facet arrangements and proportions have been perfected by both mathematical and empirical analysis. Also popular are the fancy cuts, which come in a variety of shapes, many of which were derived from the round brilliant. A diamond's cut is evaluated by trained graders, with higher grades given to stones whose symmetry and proportions most closely match the particular "ideal" used as a benchmark. The strictest standards are applied to the round brilliant; although its facet count is invariable, its proportions are not. Different countries base their cut grading on different ideals: one may speak of the American Standard or the Scandinavian Standard (Scan. D.N.), to give but two examples. History Ancient India The process of diamond cutting has been known in the Indian subcontinent as early as the sixth century AD. A sixth-century treatise Ratnapariksa, or "Appreciation of Gems", states that the best form in which to have the diamond is in its perfect natural octahedral crystal form, and not as a cut stone, indicating that diamond cutting was widespread practice. Al Beruni also describes the process of diamond grinding using lead plate in the 11th century AD Agastimata written before 10th century states: A 12th- or early 13th-century diamond ring attributed to Muhammad Ghauri contains two diamonds whose crude octahedral natural states