[Jewelry making - Article 01653] - Re: [Orchid] Micro pitting in white gold castings

[Mark Parkinson]

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    I would like to thank everyone for their replies, it's just
    remarkable to have so many talented and experienced people willing
    to share their knowledge. I am very grateful. 

    I thought I would try to summarize the responses; 

    First, as far a identifying the problem. The consensus seems to be
    that what we have is shrinkage rather than gas pits. 

    It was said that gas pits tend to be more spherical and are usually
    found throughout the casting, while shrinkage usually occurs in
    heavy areas, has spongy pores that are really small tears. 

    Suggested remedies; 

    - Sprue from thick to thin, your objective being that you want a
    homogeneous and smooth flow rate. Spueing from thin to thick will
    nearly always cause problems. 

    - Keep your flask temperature for white gold as low as possible to
    get good fill with your machine (700-900 was suggested, but that
    depends on the type of machine). 

    - Try to reuse less than 30% of white gold in castings. There were
    some good suggestions on how to reuse a greater percentage and how
    to super clean the buttons for reuse. 

    - Regularly calibrate your kiln. Using ceramic cones is an
    inexpensive and reliable method. 

    - Use a fairly substantial button with white gold. 

    - Cast heavy and light weight white gold castings separately so you
    can adjust your flask temperature down further for the heavier
    castings and a little higher for the lighter ones. 

    - Let the flask soak at the casting temperature for a couple of
    hours to insure that its at that desired temp inside the flask. 

    - Keep you initial burnout stages long and at a fairly low
    temperature to soak the flask well and remove all of the wax like a
    dewaxer would do. 

    - Keep you crucibles clean in an effort to remove any contaminates
    that inadvertently found there way there. 

    - If possible, it's better not to cast in your polishing area. It is
    a likely source of contaminates. 

    If I did not include anybodys valuable suggestion, please accept my
    apologies for the oversight. We'll put the ideas that we were not
    already doing into practice and see what happens. Goldsmithing is
    one of those jobs where the longer you do it and the more you know,
    the more you realize how little you know. 

Best regards to all,
Mark
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