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Plating-off (was firestain)

On 08-Jan-97, Kenneth Gastineau wrote aboutRe: Firestain on silver:
KG> Richard:

I am curious to try the
KG> deplating method you have described. What is involved? What
KG> chemicals are used. What type of surface is left? I have no
KG> plating experience, but would be willing to try anything that
is KG> effective and manageable for production work.

G’day: I have used the plate-off method, and it does remove
firestain. You have to use the dreaded cyanide bath (sodium
cyanide; the potassium salt is much more expensive) - strength
not all that important, and use a few volts of DC electricity,
but you wouldn’t need more than 6 volts. You connect the silver
item to the POSITIVE side of the battery, and fully immerse it,
and a stainless steel electrode to the NEGATIVE pole. Thus the
silver will be removed from the surface of the article and be
transported through the cyanide solution to the stainless steel,
where it can be recovered by peeling off. You have to watch it,
though for if the voltage is too high you will leave little pits
in the article. You will need some way of controlling the
current. Bubbles will arise from the electrodes, and should be
kept very small and not too many. If you havent used too high a
current, buffing with tripoli and rouge in the normal way will
give a good finish. You can also use this method for etching
silver if you mask off the areas you want to leave high. I
haven’t tried using the photo etching compounds, but can’t see
why they wouldn’t work well. But when the tiny bubbles reach
the surface of the solution they will carry cyanide into the
atmosphere (called an aerosol) so use a proper chemical absorbent
cannister in your mask and wear gloves. Incidentally drinking
cyanide poison to do away with oneself isn’t a good way; you die
true enough; but in agony! Oh by the way - years ago I bought a
liquid from Johnson Matthey which was supposed to act as the
electrolyte to de-plate silver and leave a mirror finish, but I
couldn’t get it to work consistently, though it did work
fleetingly. Have fun.

   / /    John Burgess, 
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