“ Imitations of sardonyx have been made by cementing together two or three stones of the required col ours, while baser counterfeits have been produced in paste. By coating a sard or carnelian with sodium carbonate and then placing the stone on a red-hot iron a white layer may be produced, so that a. kind of sardonyx is obtained (see Carnelian) . Most of the modern sardonyx is cut from South American agate, modified in colour by artificial treatment. ”