Precision cutting, also called custom cutting, is a combination of faceting techniques and machinery facilities which allow us to cut the stones using original faceting designs and to get spectacular results in precision of angles and symmetry of the stone, together with exceptional polishing quality of the facets. Precision cutting is used mostly by professional lapidaries and hobbyists in USA and Europe, while commercial cut, also called native cut or origin cut is mostly done in the countries where the gems have been mined.
Lots of comercially cut stones on a jewelry show.
In commercial cutting, the lapidary usually tries to save as much weight of the rough stone as possible, with no care of angles and brilliance of the stone. The quality of polishing and symmetry is also normally quite low. That’s why low quality commercially cut gems are sometimes bought as a rough for re-cutting, the aesthetic improvement of gems makes it profitable, even with the weight loss and additional faceting costs.
Commercially cut stones are usually sold in huge lots, while every custom cut stone is unique.
Precision cutting uses the meet-point faceting technique. Every step of the cutting process is determined by objective coordinates and references to other facets, achieving perfect symmetry and angle precision results.
Poorly cut sphalerite (left): lack of symmetry in general outline and in individual facets, bad polishing,
external cavities, general lack of brilliance, compared with nice precision cut sphalerite (right).
Regarding the equipment for precision cutting, modern faceting machines allow to fix the angles using digital dual with up to 0.01º precision. Such machines are much more expensive than those used for commercial faceting. On the other hand, new generation of grinding and polishing discs and materials, make possible to get very high quality polishing in every surface type.
Precision cutting of gemstones with original designs can be compared with "Haut Couture" dresses, in contrast with cheaper "Prêt-à-porter" commercial cutting. Very good review of precision versus commercial faceting is published in this link: A Cut Above by John Dyer.
Sphalerites offered at this site are faceted using precision cutting techniques
and Graves Mark 5XL faceting machine.