facettering

Facettering, or gem faceting, is the craft of shaping a gemstone by cutting and polishing flat surfaces called facets. The goal is to optimize light reflection and refraction through the stone to enhance brilliance, fire, and color. The resulting pattern typically includes crown facets, pavilion facets, a girdle, and a table, though designs vary by gemstone and style.

Modern facetting emerged with the development of mechanical faceting machines in the 20th century and was advanced by theoretical work on light performance, notably by Marcel Tolkowsky in the early 1900s. The field combines precision geometry, mineral science, and skilled handwork to balance proportions, symmetry, and polish.

The process begins with selecting a suitable rough gemstone and choosing an optimal cut. The cutter mounts the stone on a dop and uses a faceting machine with an index wheel to position facets at exact angles. The stone is successive ground and polished on progressively finer laps, with careful attention to facet alignment, girdle thickness, and culet size. The result is a faceted gemstone whose brightness and dispersion depend on accurate angles and a high-quality polish.

Materials used include diamonds and a wide range of colored stones such as sapphires, rubies, emeralds, and quartz. Some stones are more prone to cleavage or fracturing and require gentler handling and tailored angles. The craft demands steady hands, mathematical planning, and specialized equipment.

Quality in facetting is judged by symmetry, proportion, polish, and overall light performance. Well-faceted stones exhibit superior brilliance and color dispersion, making faceting a distinct and highly technical branch of gem cutting.