one school of thought holds that if iron is introduced into the
pickle, it (the pickle) is permanently contaminated and must be
changed. ... ... several people advised that one could introduce
iron to the pickle, flash plate a piece, remove the iron and all
would be well again.
It’s a little of both, but mostly the second.
What happens when you introduce iron into pickle is that some iron
dissolves, forming iron sulphate. Now, if the iron is IN CONTACT with
your silver or gold, AND there is already copper oxides dissolved in
the pickle (which when dissolved forms copper sulphate), then the
contact of the iron and the silver or gold forms an electrochemical
cell. A battery. The iron is more chemically reactive than the
dissolved copper. so the reaction that can take place which most
conserves energy is that the dissolving iron displaces copper, which
then literally electroplates back out. But for this to happen, the
reaction needs currently dissolveing iron in contact with the silver
or gold. You can have iron in the pickel and not disturb silver that
is not part of the circuit (electrically connected to the iron),
though if it’s close enough, you can get a partial circuit forming
just through the liquid too, if there’s enough copper in solution.
But mostly, it needs iron, as iron, in contact with the silver. Once
the iron is already dissolved, it’s pretty much out of the picture in
this regard. So if you briefly make a mistake and dip some iron in
the pickle, and copper flash your piece, if you then remove the iron,
most likely the pickle is not ruined.
but the other side of it is that if you get ENOUGH iron, (or several
other chemicals) contaminating the pickle, then it’s possible for
other effects to occur. Usually more subtle, like items starting to
come out of the pickle looking dingier. And if there’s enough iron in
there, that that too can, in some instances, start to plate out,
especially when alloys containing zinc are in the pickle. the result
is usually yellow or rose gold items coming out the pickle looking
somewhat paler and dingier than you’d expect.
Most of this is common sense. If your pickle is badly contaminated
and full of junk, replace it. You’ll know when it’s time because it
won’t be working right any more, or your pieces will be etching or
coming out dingy or discolored in ways you didn’t expect. But you
don’t need to do the Knee-jerk reaction of replacing it the moment
some iron has touched it either.
And on that subject… if your item has come out of the pickle
accidentally plated with copper, and it’s inconvenient to just buff it
off, mix up a small amount of new, cold, sparex type pickle. Add a
little hydrogen peroxide. That will remove the copper. The solution
does not last long, so discard when done.
That dingy whitish look that comes from really trashed pickle will
sometimes clean up with just a bit more time spent in your newly mixed
And another useful conclusion to the discussion of copper plating is
this: If/when you break a drill bit or burr, or bit of sawblade, even,
in your work, one of the easiest ways to remove it is just to soak it
in the pickle, which dissolves the broken drill bit. It also causes
some copper plating, often mostly around the drill hole, if the pickle
is older and contains dissolved copper. If it’s new, it won’t plate
out 'cause there’s no copper in the solution to deposit. Either way,
you don’t then have to replace the pickle just 'cause you used it to
etch out a broken drill tip… Nor do you have to absolutely avoid
using your regular pickle to remove that drill bit. Just don’t pickle
it with a bunch of other good items at the same time.
Hope this helps.