[Jewelry making - Article 00103] - Re: [Orchid] Yellow gold turned red after soldering

[Ala]

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    Many mass-produced 9ct or 10ct chains are flash plated in pure gold
    to 'improve' the colour. The aim of flash plating is to get no more
    than a few atoms thickness of pure gold onto the surface. When the
    item is heated to soldering temperature the plating disappears from
    the surface; I think it soaks into the metal, or it simply floats
    off on the oxides of the body metal. Either way you are left with
    having to re-plate the affected area to return it to the same colour
    as the rest of the chain, or heat the whole chain to remove all the
    plating so that the chain is all the same colour - the colour of the
    body metal. 

    If the chain has been depletion gilded then the gold layer is much
    thicker than flash plating and it should remain after the soldering
    process. After all the soldering and pickling is adding another step
    of depletion gilding. One thing throws everything out of kilter and
    that is polishing! A quick rub of tripoli will cut through most types
    of gilding, and rouge will do it less quickly. 

    Alloys made for depletion gilding must contain a lot of copper
    because that is what depletes. The body metal of depletion gilded
    items will therefore be rose or pink gold. If you deplete yellow gold
    then the surface will be a pale colour because it contains more
    silver along with the gold in the depleted layer. 

    The best way to polish a chain is to use a fine brass brush
    lubricated with bicarb of soda. The brass bristles will burnish the
    gold layer (if gilded) making it compact and harder, and imparts a
    shine that is just short of 'polished' as we are accustomed to from
    the polishing motor. I use the brass brush on all chains gilded or
    not as the finishing process, to clean the chain before and after
    plating, and on any filigree/mesh/fragile items. The brush I use is
    a brass shoe brush, I wrap the chain around my hand and brush
    vigorously in the palm pulling the chain round and round a few times.
    The links end up polished all over inside and out, and it is far
    safer and probably quicker than using a polishing motor. 

Regards, Alastair
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