Facettierens

Facettierens is the lapidary technique of shaping and polishing a gemstone by cutting a sequence of flat facets. The facets are arranged to control how light enters the stone and is reflected and refracted, with the aim of maximizing brilliance, fire and scintillation. The method is applied to a wide range of gemstones, including diamonds, sapphires, rubies, emeralds, quartz, topaz and many synthetic stones.

Modern faceting developed in the 20th century with the invention of precision faceting machines and the use of diamond abrasives, which allowed for much tighter control of angles and symmetry. Earlier forms of facet cutting existed in various cultures, but the contemporary practice relies on standardized angles, indexing, and polished finishes to achieve consistent light performance.

The process typically involves a faceting machine that holds the stone on a dop and rotates it against a rotating abrasive lap. The cutter follows a planned facet map, grinding successive facets at carefully measured angles to build up the crown (the upper portion) and pavilion (the lower portion) of the gem, with the girdle providing a boundary between them. Key stages include blocking (roughly forming the main facets), shaping (refining the crown and pavilion), determining the table and girdle, and finishing with polishing. The typical end products are a tabletop with a set of crown facets above and pavilion facets below, aligned to produce optimal light performance.

Material considerations include hardness, inclusions, and stability, which influence abrasive choice and cooling. The quality of faceting is judged by symmetry, proportion, polish, and the resulting brightness and dispersion of light, with diamonds often evaluated against standardized cut grades, while other stones follow conventional industry practice.