Historically, many coloured gemstones have been subjected to a variety of treatments designed to enhance their appearance. Certain enhancement methods such as heating, are routinely used to improve colour or transparency in rubies and saphires. Other methods, such as oiling, enhance the clarity of emeralds. The international jewellery trade has generally accepted these methods. Other coloured Gemstones may have undergone other permanent or semi-permanent treatments, such as dying, irradiation, coating and impregnation possibly requiring further retreatment in order to retain their appearance.
Prospective purchasers should assume that all gemstones will have been treated unless statements are made to the contrary. Gemmological reports from internationally recognised Gemmological Laboratories will be noted in the item description when available.