BUYER BEWARE!!!!!! Tanzanites Treatment of gemstones to enhance their appearance is not a new phenomenon; it has been going on for centuries, with the first mention to be found in a book written in 1548. Common gem treatments include heating, irradiation, bleaching, colourless or coloured impregnation, dying and coating. The wide and consistent use of some treatments over the years has eliminated the need for disclosure – for example, one of the most commonly accepted practices is the conversion of green aquamarine to blue aquamarine by using heat. For the more drastic treatments, which can mislead customers into thinking they are purchasing a far better quality gemstone than they really are, disclosure is compulsory. The way that stones should be described and the treatments that should be disclosed are all clearly set out in the GIBJO Blue Book on Coloured Gemstones, which is widely respected as the worldwide ‘bible’ for gemstone nomenclature. The most important task for a gemmologist is to be able to identify the treatments that have been used to modify the colour and clarity of the gemstone under examination. It is generally accepted that all tanzanites will have been heat treated to transform them from the greyish brown of the rough to the vivid and intense indigo and violet hues that are so sought after. This is an irreversible process and there is no risk that the stone will fade over time, or be less robust as a result of the treatment. However, the application of a surface coating is a very different matter, as it can enhance a relatively inferior stone by as much as two colour grades, greatly inflating its value. The coating is not permanent and will eventually peel away leaving a very disappointed customer.
Posted on: Tue, 02 Jul 2013 10:41:04 +0000
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