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| Gems & Jewelry |
All That Glitters
Jill Newman
02/02/2004
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While thermal heating of sapphires and rubies and oiling of emeralds is an accepted industrywide practice, buyers should avoid stones with other treatments that may not be permanent, might affect the durability of a stone or conceal a significant flaw, advises Andrew Lucas, product manager of gemology at the Gemological Institute of America. Certain treatments, such as colored oil on emeralds, can fade over time or when a stone is cleaned.
Other common treatments include diffusion, a process that exposes the surface of rubies and sapphires to chemicals, and prolonged heating to enhance color. Fracture filling is another typical practice; it fills a stone’s fracture with oil, wax, glass or epoxy resin. While these treatments can be permanent, they will greatly reduce the value of a stone.
Leading gem laboratories have been able to detect most treatments. However, even the gem experts have trouble with some of the newest techniques. The American Gem Trade Association Gemological Testing Center has begun to encounter a new heat treatment that it cannot identify in a growing number of blue sapphires. While the lab has been evaluating and testing these sapphires for more than a year, it still does not have conclusive information about this treatment. Until it can identify the enhancement, it refuses to issue reports on the stones.
Aside from whether a gem is natural or color-enhanced, its country of origin also plays a role in determining its value. The world’s finest rubies come from the Mogok Valley of Upper Burma and are identified by a subtle florescence that exists only in gems mined in that region. The first known mined rubies from Mogok Valley date back to 1496, but Burma’s mines have been sealed off since a government crackdown in 1962, and even before that the Mogok mines were running out of reserves. The Muzo and Chivor mines of Colombia have produced the best emeralds for centuries, while Ceylon, Burma and Kashmir
are the sources of the most coveted
sapphires.
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