[Jewelry making - Article 00294] - Re: [Orchid] Rhodium plating tanzanite jewelry

[leonid surpin]

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>     I remember having rhodium plated tanzanite stuff before without a
>     hitch but just wanted to know for sure for future reference. 

    When I read original post of tanzanite changing color after rhodium
    bath, it piqued my interest. Under ordinary conditions this should
    not happen. So after thinking for a while, I can offer 3 theories: 

    1. There is another deposit of gem quality zoisite (Tanzanite) which
    not very well known. It is Alchori deposit new Scardu (India). This
    mine produces colorless to green crystals as opposed to blue coming
    from Africa. It is possible to give these stone blue coloration, but
    treatment is not permanent. 

    2. Tanzanite is trichroic. For best color, stones are oriented
    perpendicular to the optic axis. This orientation resulting in small
    yield. Orienting parallel to the optic axis would result in much
    better yield, but the color would suffer. With some "gemological
    magic" the color can be improved, but as mentioned before nothing 
last
    forever. 

    3. It is possible that after plating, the inside of the setting
    became reflective, that would change the optical path of light
    through the stone. Since Tanzanite colour is direction sensitive,
    that could result in the observed effect. 

Leonid Surpin.
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