[Jewelry making - Article 00055] - Re: [Orchid] Coloring 18k yellow gold

[Dreamgate9]

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    Beth, Basically, what you are doing is removing some of the alloy
    metal on the surface by converting it to an oxide, then removing the
    oxide. Copper is the metal that most readily oxidizes, so alloys
    containing a lot of copper seem to depletion guild best. 

    14k yellow has less gold than 18k, so you have to remove more
    surface alloy that you would with 18k, but it works (as you know).
    Alloys with a good bit of silver in the mix, like green golds, tend
    to get a bit greener with all that silver left on the surface. I
    usually give them a dip in the nitric bath, and that seems to remove
    the surface silver. What I have now is a lot of gold on the surface,
    with the gold+alloy underneath. If you polish too aggressively,
    you'll remove this surface layer. Brass brushing is a good idea, as
    it burnishes the gold surface without removing metal. 

    If you are using commercially prepared alloys, you can't always tell
    what you'll get until you experiment a little, since they're all
    different and the refiners don't like to tell you what's in their
    "special mix." If you are alloying your own, you have a lot more
    control. Sparex (sodium bisulfate) will work. I have a pickle that I
    use just for depletion guilding. It is a weak solution of sulfuric
    acid, with a pinch of sodium dichromate. The sodium dichromate acts
    as an inhibitor that allows the pickle to only attack the oxide. I
    am also using an 18k alloy with a lot of copper (15%). 

    I know there's a lot more science to this, but this is the basics of
    how it works. 

Doug Zaruba


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