This is almost certainly the result of two things: the pickle has
dissolved some copper as a result of being used for some time (it
probably looks slightly blue), and you accidentally immersed some
iron with the gold pieces (possibly a steel spring in a clasp, or a
steel jump-ring). Fresh pickle won't do this, even in the presence of
I once made some complicated earrings out of white gold chenier.
Since the chenier had to be bent to quite a small radius I originally
made it with a copper core that I thought could be dissolved with 10%
sulphuric acid, but it didn't work; the copper appeared untouched
even after a day or so.
Although I'd read previously that a core of soft iron was
recommended I was also aware of the problem of iron causing the
copper to be deposited, so I tried an experiment; I left a loop or
two of the copper filled chenier in the acid and dropped an iron nail
in too. The iron fizzed a bit, but after several hours there was no
visible copper on the gold and the nail was visibly attacked so I
remade the chenier on a soft iron core and put it the acid again.
This time it worked; the iron was dissolved OK (took a day or so),
but to my surprise, the white gold got plated with copper.
From this I learned that the iron has to touch the gold for the
copper to be deposited. This would explain why one item was plated
and the other not; the one that was plated was touching the iron.
I found that 30% nitric acid removed the copper in a few seconds. I
put the acid in a small jar, took it outside into the garden,
suspended the earrings on a bit of nylon cord, and dipped them in.
They fizzed like a Selzer tablet for a few seconds, and when it
stopped I removed them - the copper was gone. I thought the nylon
wouldn't be affected by the acid, but I was wrong. A few minutes
later the nylon just broke - but it had already done its job.
I hope this helps.
Regards, Gary Wooding