[Jewelry making - Article 00334] - Re: [Orchid] Fire scale Prevention During Vacuum Casting

[jkbrennan]

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>     Is it the silver that has a high affinity for oxygen or the copper
>     part of a sterling alloy? I have never seen firestains on fine silver
>     castings.

    Molten silver dissolves up to about 30 times its volume of oxygen.
    as it solidifies the oxygen comes out  and can cause a lot of
    porosity. Fine silver does not get "firescale" but it can get
    porosity. 

    The copper in sterling can  react with  oxygen  and trap it at and
    below the surface causing "firescale". 

jesse


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