NEW YORK, NY - 23 May 2008 - Recently the American Gem Trade Association Gemological Testing Center (AGTA-GTC) and American Gemological Laboratories (AGL) received a number of faceted tanzanite samples that were determined to have been coated. Evan Caplan of Omi Gems, Inc. sent samples to several labs after a light repolishing of a few stones resulted in a noticeable loss of color.
“Until now, we had not identified a coating on tanzanite to improve its color.” indicated Dr. Lore Kiefert, Director of the AGTA-GTC. “Although the coating is not immediately obvious, careful examination with a microscope and in immersion provided clear indications of the coating in most instances.” stated Christopher P. Smith, Vice President and Chief Gemologist of AGL “This was evidenced by abrasions along facet junctions and at the culet where the coating had worn off, as well as a subtle iridescence when viewing the surface with reflected light.” Smith further added.
Advanced analytical testing identified that the coating contained cobalt. “The most reliable means to substantiate the presence of the coating is the use of X-ray fluorescence spectroscopy.” Kiefert explained “The coating is colored by cobalt, which is readily detected using this analytical technique.” Although the gemstone industry has become very familiar with the practice of heating zoisite to achieve the best violet to blue color in tanzanite, these stones represent the first time either lab has identified a color-enhancing coating on tanzanite.
The majority of the tanzanite sample was comprised of smaller calibrated stones. Fine color tanzanite in this size range is rarely sent to a lab and therefore would avoid detection unless closely scrutinized. “This is just another reminder that each and every gemstone should be fully examined to determine whether or not it has been treated.” Smith indicated “Today, it is not uncommon to see stones that have been treated using multiple or compound techniques to achieve a particular result.” As a closing statement, both Kiefert and Smith emphasized “Any treatment used to modify the color of a gem should be disclosed. Coatings in particular are not considered permanent and in the U.S. are required by FTC guidelines to be properly disclosed at the point of sale.”
About American Gem Trade Association-Gem Testing Center
The American Gem Trade Association is a not-for-profit
Association serving the natural colored gemstone and
cultured pearl industry since 1981. The AGTA serves
the industry as "The Authority in Color"
and has its headquarter office in Dallas, Texas and
the world-renowned Gemological Testing Center in New
York, New York (www.agta-gtc.org).
About American Gemological Laboratories
Founded in 1977 by C. R. “Cap” Beesley,
American Gemological Laboratories (AGL), a subsidiary
of the publicly traded Collector’s Universe
(NASDAQ: CLCT), pioneered the development of the world’s
first comprehensive Colored Stone Grading System (www.aglgemlab.com)
AGL has also provided detailed country of origin and
enhancement reports for some of the most prestigious
retailers and auction houses in the world for the
past three decades. In 2007, AGL was the designated
official North American laboratory of the International
Colored Gemstone Association (ICA). In addition, the
laboratory is the official colored gemstone laboratory
of the 2007 Fine Jewelry CEO Summit and the JCK Las
Vegas Shows, as well as the 2007 Platinum Sponsor
of the ICA World Congress in Dubai.
