Sardonyx is a variety of chalcedony quartz with parallel bands of reddish-brown sard alternating with layers of white or black. Its distinct, evenly layered structure made it the classic stone for carved cameos and intaglios, in which the carver cuts through the upper layer to leave a figure standing in a contrasting colour against the ground.
Sardonyx was prized in the ancient world, where Greek and Roman gem engravers used it for seals, signet rings and portrait cameos, and it was revived enthusiastically during the Renaissance and again in the neoclassical period, when collections of antique gems were formed by Grand Tour travellers. Victorian jewellery made extensive use of sardonyx in brooches, rings and lockets, often set in gold. It was also used for snuff boxes, vessels, seals and desk accessories. Collectors look for crisp, well-drawn carving, clean separation between the layers and good colour, while chips, cracks and later repolishing reduce value. Distinguishing ancient from later gems is a specialist matter, and many sardonyx stones on the market have been dyed to strengthen their colour, a practice of long standing that should be noted when describing a piece.
