Silver color over copper sheet

We had a very interesting occurrence at the Art League Jewelry
Department this last Wednesday.

A new student of mine had built a copper model of a ring that she
wanted to produce in silver, & I suggested to her to tumble barrel
the piece for a quick finish.

She brought it back to me later, & the whole piece was now silver -
honest - of course she asked me what had happened - I was thinking -
how can we market this! Then I thought my other students were
pulling my leg.

So we put a piece of sheet copper in the tumbler, & yet again it
came out silver in color.

What is going on here?

Here’s the facts - the piece was copper; the tumbler was a standard
Lortron barrel tumbler, with stainless steel shot - Rio’s super
sunsheen burnishing compound + water. Nothing else was in the barrel
that we could see.

The only odd thing was that my new student had chosen the barrel
shot we usually reserve for PMC - no pin shot, only rounded shot.

Is it possible that particles of PMC can be retained by the
stainless steel shot, & then re-deposit it onto a base metal?

So of course, all my other students threw their copper pieces into
to barrel - some pickled; some not - all the pieces came out
silvered, but the one’s that weren’t pickled had a lesser, more
mottled deposit of the silver color.

My other concern is that I know mercury can coat metal - to what
extent I don not know, & I don’t know how that could have
contaminated the shot, but would this account for it?

I look forward to your comments

You have silver in an ionic state in the tumbling solution. the
copper is more cathodic than the stainless so the silver plates out
on the copper. It is just like plating copper on silver when iron is
introduced into the pickle pot.

James Binnion
James Binnion Metal Arts