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January/February
2002 |
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| New Sapphire Treatment Still a Mystery By Marlene A. Prost
The controversial treatment used in Thailand to produce padparadscha color in pink sapphire is a new process that may prove difficult to classify. That is the preliminary conclusion of the Gem Trade Laboratory of the Gemological Institute of America (GIA) in Carlsbad, California, published on January 28 in the GIA Insider. Spurred by concerns by a number of gemologists and dealers, the GIA spent several weeks studying 48 pieces of corundum in an attempt to identify the mysterious new process being used by gem heaters in Chanthaburi, Thailand. The process turns Madagascan pink sapphire pink/orange; green sapphires from Songea, Tanzania, orange; and purple-red Thai rubies orange-red. The GIA’s conclusions may not end the controversy that began last fall when large quantities of the treated, padparadscha-colored sapphire started appearing in Chanthaburi. Thai-based suppliers and laboratories, including high-profile Thaigem.com, are promoting the padparadscha-colored sapphire as heat-treated. However, some American gemologists have been skeptical. Richard Hughes of Pala International of Fallbrook, California, was one of the first to warn that the treatment was not being properly disclosed. “We do not believe it is a standard heat treatment. It is probably a surface diffusion treatment,” said Hughes a week before the GIA report came out. The evidence is in the stones themselves, say critics. While heating causes the color to change throughout the stone, these sapphires have a rim of orange along the three-dimensional outline of the stone, leaving a pink core -- a classic sign of diffusion treatment. However’ the GIA’s report says the treatment is something other than surface diffusion, in which the surface color of a stone is changed by infusing a new chemical element. One major difference is that in a few stones they examined, the orange layer penetrated more than half the distance to the center, while one stone was 80 percent orange. Regardless of the method, it should be disclosed, the GIA stresses. Until more information is available, Gem Trade Laboratory identification reports will note the color zoning in all orange-colored sapphires. Thais Defend Treatment On January 28, the CGJA announced that tests conducted by the Gem and Jewelry Institute of Thailand (GIT) confirm the pink sapphires were subjected to heat treatment and not diffusion. According to the GIT’s report, their chemical analysis showed no unusual trace elements except for a high amount of iron (Fe³). “These chemical results seem to suggest that no color-causing elements, in particular the iron, were added to these stones during this new heat-enhanced technique,” said the report. The GIT’s results were essentially the same as the GIA’s, although the GIA report called for more advanced testing for potential color-altering elements. The CGJA release asserted that the process is simply heat-treating, nothing more. Meanwhile, the uncertainty has left many sapphire dealers in limbo. Many, even those who have already purchased the sapphire under false pretenses, assert that they will not sell the disputed material until the controversy has been settled. For more on this story, see the March/April issue of Colored Stone |
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