Feature Gems & Gemology, Fall 1981, Vol. 17, No. 3

Heat Treating Ruby and Sapphire: Technical Aspects

Ruby and sapphire of natural or synthetic origin can be heat treated to improve asterism; to remove asterism or silk; to improve, add, or remove color; and even to alter imperfections. At least nine distinct processes can be identified, although several may occur simultaneously. Some of these treatment methods correspond to natural processes and may not leave any evidence of their use; others do not correspond to natural processes and are readily identifiable.