New tanzanite treatment identified
Friday, May 30th, 2008
The American Gem Trade Association Gemological Testing Center (AGTA-GTC) and American Gemological Laboratories (AGL) have discovered a surface treatment for tanzanites to improve their color. It was discovered after a light repolishing of the stones resulted in a noticeable loss of color.
The treatment is not permanent and is not immediately obvious when examined. Testing pointed to cobalt in the coating which is easily detected using X-ray fluorescence spectroscopy Lore Keifert, director of AGTA-GTC said. Additional evidence showed in abrasions, or scratches, and the facet junctions and culet where the coating had been worn off.
While heat treating for color has been around for years for tanzanite, this newly discovered treatment seemed to focus on smaller, calibrated, gems that are not normally tested due to their size and relative value.