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Vinegar pickle plating


#1

Hello!

I am a beginning metalsmith making a multimetal piece (a fairly big
chain) and have encountered something that threw me for a loop the
other day.

The links in the chain are mostly non-ferrous metals, with two links
containing some twisted iron wire. All along I have pickled the
non-ferrous metals as usual in sparex being careful to keep the
sections with the iron-bearing links separate, no problems. I
pickled the short sections with the links with the iron wire in a
hot vinegar + salt solution I read about here, and that worked
perfectly well for those.

The problem came when I got the whole seven feet of it together and
figured that I had better pickle the whole thing in vinegar and salt
to avoid copper plating the numerous sterling links due to the two
links with iron.

I put it in a clean pyrex bowl with the hot vinegar and salt and
upon checking back on it a little while later was mortified to find
that the whole thing had a lovely pink glow!

Now, following another tip I found here I submerged it (while
carefully holding the two iron-bearing links OUT of the solution!)
in a sparex + 3% hydrogen peroxide solution. Voila, the copper came
off the sterling (and everything else) like magic very quickly. You
had better believe I stood there watching it like a hawk, though. It
went fast!

The problem is fixed but I am still very puzzled as to why it copper
plated in the vinegar and salt solution. I specifically opted for
that as a final pickle because I thought it would not plate with
iron in it! Was it the salt? What the heck was going on there? What
did I do wrong?

Thanks in advance for answers to this little mystery!

Also, I want to send a huge thanks to the list for providing so much
valuable Most recently James Binnion’s on
bronzes (brasses) and how they behave after soldering/pickling in
the last month or so- immediately helpful and useful to me. It has
made a HUGE difference in my practice and has helped me solve
numerous problems in the studio. This is an amazing resource.

Bonnie


#2
Why does iron cause copper to plate out when  vinegar and salt
solton is used as the pickle? 

It’s because any source of copper ions in solution will tend to
plate those ions out on iron as metallic copper, while the iron goes
into solution to replace the copper. This is just chemistry: the
fact that iron is more galvanically active than copper is.The effect
of salt and vinegar together is to cause the solution to act like a
mixture of hydrochloric acid and sodium acetate, which readily
dissolves copper oxides when used as a pickle. So there you have the
Cu ions in solution, and all you have to do as add metallic iron to
precipitate the copper as a thin coating.

Dick Davies


#3

Dear Bonnie,

All the salt did was to make the vinegar pickle stronger- thus the
pink color from the iron links. Any acid is going to cause the iron
links to turn the solution pink. Perhaps you could use another metal
instead of the iron? Bill Seeley from Reactive Metals came up with a
pickle formula years ago that consisted of hydrogen peroxide and
distilled white vinegar. I used to use the formula when I worked
exclusively in copper & brass. Otherwise, I am happy with Sparex.

Ruthie Cohen