[Jewelry making - Article 01311] - [Orchid] Green and black on new castings

[Kathy Johnson]

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    I cast a lot of sterling charms last night. On nearly every newly
    cast tree of charms as they came out of the investment after
    quenching, the small base of the tree and a few mm. up the tree
    sprue, had a surface coating of mottled green. It looked very much
    like verdigris on copper. It came off in the pickle, but underneath
    the green was a very heavy layer of something black that won't come
    off. Fortunately the black is only on the sprue bases, so the charms
    weren't damaged. 

    This has never happened before. The only thing that has changed is
    that my electromelt was recently repaired--it got a new themocouple
    and heating element. This is the first time it's been used since the
    repair. What could have caused the green and black layers on the
    castings? What is the black stuff, and how can I get it off the sprue
    bases so I can re-use them when I cast again? 

Kathy Johnson
Feathered Gems Jewelry
http://www.fgemz.com

 
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