[Jewelry making - Article 00250] - Re: [Orchid] Reconditioning used crucibles

[Peter W . Rowe]

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>     I have noticed that apart from and acid smell when the crucible is
>     used for the first time again there is a purifying effect on the
>     gold. 

    There would be. The residual Hydrochloric acid would contribute
    chloride ions to the melt. The result would be about the same as
    adding a pinch of ammonium chloride (sal ammoniac) to the melting
    metal. It bonds with baser metals forming insoluable chlorides,
    which then slag off, leaving the gold and silver slightly purer.
    Reduces things like zinc, tin, iron, etc, from the melt. Note that
    the fumes you're smelling are Chlorine gas. Use those newly cleaned
    crucibles with enough ventillation so the smell is not all that
    strong. It's not friendly stuff to lungs (neither, of course, are the
    direct acid fumes).

Peter


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