[Jewelry making - Article 00310] - Re: [Orchid] Brittle gold-about alloys

[James Binnion]

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    And anyone who knows John Donivan knows what a great wealth of
    experience in bench work he has and shares with others :-)  Anyone
    who knows me knows I can get a little picky about the details :-) 

    John, it is with your last statement there where I have a little
    quibble :-) 

    However, it remains, that in practical terms, the everyday alloys
    used in the jewelry industry are firmly bonded. 

    This should be true if the alloys are properly processed, however 
    more often than we would like alloys are not processed quite right. 
    If alloying is done in the crucible just before casting the
    resulting alloy can be not mixed very well or worse yet foreign
    items can be introduced into the melt like old investment odd bits
    of metal like iron from bench sweeps etc. or crucibles are not kept
    separate for different metals so bits of say nickel white get into
    yellow because only one crucible is used for gold. Anyhow there are
    many ways that contaminated metal can end up in a ring and this can
    lead to the kind of failures that we have been talking about.
    Impurities tend to segregate in the interstices between the crystals
    and cause areas that are susceptible to inter-granular corrosion or
    brittleness. 

Regards,
Jim


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