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Burning sterling silver when polishing


#1

G’day to you John and Virginia Just wondering whether the depletion process
actually removes firescale. John perhaps you could give some insight into
this with your wealth of knowledge. I have been pickling, brass brushing,
and pumicing my pieces around 10 times to bring up the fine silver. The
colour is beautiful and white and whilst I never polish any of my work,
these steps could be adopted before polishing - it sure beats filing,
sanding and white dipping. Regards Christel from freezing(tonight) West Oz


#2
    G'day to you John and Virginia Just wondering whether the depletion
process actually removes firescale. 

G’day; the ‘depletion process’ will certainly remove the surface layer of
copper oxides. But if the penetration of the oxidation is deep, then even
more drastic action to get at the entire depth of the oxidation layer will
be necessary. Every time the work is heated it may in fact increase the
depth of the oxide penetration if oxygen can get to it.

As I said, Pripps and similar anti-oxidant coatings do help, but the answer
is to make your soldering and other heating cycles as brief as possible
and at as low a temperature as will give you a good result. Just keep in
mind that the pickle attacks the thin surface layer of copper oxides and
NOT the silver or gold, so that you are left with a copper free surface of
nice clean silver. But there may still be copper oxides below this, and
that horrible grey patchiness which may be seen on buffing is simply due to
the removal of the extremely thin pure silver coat to reveal remaining
copper oxides. Whether you remove this by re-sanding, cratex wheels, heavy
polishing with tripoli or bobbing, or by nitric acid dip or by plating off
the surface layers, is up to the operator. But one or more of these
possibilities have to be faced.

The air around my work place tends to become as blue as old pickle when I
get that greyness instead of a lovely bright clean polished surface.

I have been pickling, brass brushing, and pumicing my pieces around 10
times to bring up the fine silver. 

What you are doing in effect is giving your work a coat of pure silver,
much as electro plating will. Cheers.