[Jewelry making - Article 00896] - [Orchid] AGTA and AGL Identify New Tanzanite Treatment

[AGTA]

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    FOR IMMEDIATE RELEASE 

    AGTA GTC and AGL IDENTIFY COATED TANZANITE. 

    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 tobe 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 was composed
    at least in part to cobalt. "The most reliable means to substantiate
    the presence of the coating is with the use of X-ray fluorescence
    spectroscopy." Kifert 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 coating on tanzanite to further improve its color. 

    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 a further 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 orcompound 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." 

    http://www.agta.org/pressroom/images/20080528figure1coattanz.jpg 

    Figure 1: These two tanzanites were part of a group of stones
    recently examined at both the AGTA GTC and AGL facilities in New
    York. Both were identified as having a thin coating layer to
    artificially improve their color. Photograph by Fred Kahn and Sun
    Joo Chung. 

    http://www.agta.org/pressroom/images/20080528figure2coattanz.jpg 

    Figure 2: The cobalt-coating produced a subtle iridescence that
    could be seen when observing the stone's surface in reflected light.
    The rectangular area near the point of this facet also highlights an
    area on the host tanzanite where the coating did not adhere.
    Photomicrograph by Christopher P. Smith 

    http://www.agta.org/pressroom/images/20080528figure3coattanz.jpg 

    Figure 3: In immersion it was also noted that along facet junctions
    and at the culet the color was lighter. This was a result of where
    the coating had been abraded away, revealing the lighter, inherent
    color of the tanzanite. Photomicrograph by Christopher P. Smith

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