I've spent the last day and a half trying to take the copper colour off a piece I'm working on. I made fresh hot pickle, I left it in overnight, I left it in all day yesterday, I tried the hydrogen peroxide trick...nothing seemed to help. And I was quite baffled as to why only one component had gone pink when even the piece of silver soldered to it was fine.

Finally this morning I recalled that I had some notes about the failed experiment in wire knitting that I'd recycled to make the bit in question. Turns out it was actually silver-plated wire, not sterling.

I've succeeded in taking off the plating, all right - but it was silver plate from copper, not copper from silver!