I tried to anneal some sterling wire in my kiln. It annealed just
fine but it is REALLY discolored (I didn't put any flux on it).
I've tried pickling it in swimming pool acid mix and that hasn't
done fixed it. What can I use that might really clean it for good?
Several comments. First, what sort of acid are you using? There are
several acidic products used in swimming pools. Some are based on
hydrochloric acid or similar chlorides, and won’t do a thing for
cleaning/pickling silver, because silver chloride is not water
soluble, so the acid forms an insoluble film on the surface and any
further effect stops. If anything, the chloride based products can
make the metal look even worse than it does, since after a short
while exposed to air and light, the chloride layer itself turns dark
For proper pickling, make sure the chemical is sodium bisulphate.
This is the same stuff packaged as pickle for jewelers such as Sparex,
but the pool chemical guise for the stuff usually is less costly, and
sometimes seems purer than the versions sold to jewelers. Usually
sold with a name like ph-down, spa-down, or the like. This is used
only to reduce the ph in spa and swimming pool water, unlike the more
common chloride based products which are used to chlorinate the pool
as a disinfectant and to prevent algae, etc. The chlorides don’t
clean off your sterling. The sulphate, essentially a sulphuric acid
salt which acts just like dilute sulphuric acid but is safer to
handle, will pickle off the outer black oxide layers leaving you with
a matte white surface.
You cannot, by simply pickling, get back to the clean polished
surface you had after drawing the wire, and pickling only removes the
surface black oxide. It leaves a thin surface layer of fine silver
(the white matte surface), but underneath that, to a certain depth
into the silver, the copper content of the sterling has also
oxidized, giving you what is called fire stain. (the initial black
surface is fire scale). fire stain shows up as a creamy to almost
reddish coloration of the metal that often isn’t easily visible until
you go to the final stages of polishing. Often you get areas where it
remains as blotches on the metal where others have been buffed
through to the clean unoxidized core of the sterling, which then
polishes better and has a darker clearer color.
Removing the fire stain usually is done by buffing through it, which
tends to make your wire thinner. It can also be removed by bright dip
acid baths, but these equally work by etching off some of the surface
metal to get below the oxidized layer. The latter may work in your
case, if you’re planning to draw the wire down more than you have
now, since after the bright dip, the wire may be uneven in thickness
and have a somewhat roughened surface from the etch. But another pass
through the next smaller hole in a drawplate would clean up the wire
well enough. There’s less benefit to doing this if you haven’t take
the step beyond pickling, to remove the fire stain as well as the fire
scale. Drawing would give you bright looking wire (if you pickle it
to a white surface first), but when you polish your finished piece,
you’d still find the fire stain on the wire.
Solutions are generally to prevent formation of the fire scale and
fire stain in the first place. A prips flux coating will do it, as
will a good coating of many other types of suitable fluxes, or the use
of an atmosphere controlled furnace for annealing so the metal never
is exposed to oxygen in the process. The other main solution is to
use one of the new types of sterling, like argentum silver, that
simply do not form this annoying deep oxide layer.