[Jewelry making - Article 00657] - [Orchid] Larimar tarnish, oxidation?

[johnandgervaise]

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    I have been working with larimar for the past 12 months or so and
    have generally been happy with the results. I have mostly been
    working with high quality rough (deep blues, few if any fractures,
    very few patches of the dark gray matrix). However, some of my rough
    appears to oxidize? once it is exposed to water ( I use a synthetic
    oil/water lubricant [lube 4800] with the saw, straight water (soft)
    for grinding, and diamond for polishing). 

    What I find is that brown/rust orange plumes begin to infuse the
    surface and then the interior of the stone. It looks rather like the
    plumes of a plume agate, however it is very undesirable to see a
    beautiful piece of valuable deep blue solid larimar become ruined
    with plumes of reddish/rust brown color. The process sometimes only
    takes 15 or 20 minutes to become noticeable, and the plumes can
    eventually cover the surface of a 2 inch square slab. These plumes
    usually start from the outer edges of the stone, I believe they may
    be some sort of tarnish or oxidation (iron oxide?) from impurities
    in the stone that is reacting with the water. However there does not
    appear to be any rhyme or reason to the appearance of the brown
    plumes - I have tumbled a batch of end cuts and pieces and there was
    not a sign of any discoloration (and these pieces were in water
    polish slurry for a month!) 

    Has anyone had a similar experience with larimar? Any thoughts on
    how to avoid the formation of this oxidation/tarnish (it would be
    difficult for me to polish only with oil based lubricant - not sure
    if that would work anyway)? Is there some way of "clearing up" or
    treating the brown plumes perhaps with acid??? Any thoughts or help
    would be greatly appreciated. 

Thanks,
John
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