We changed the acid and all was fine.
Might have been something in the gold alloy, but rest assured it
wasn’t the gold. Pickle dissolves metal oxides. Gold doesn’t oxidize.
After heating, any oxides on a piece of gold are generally from
copper, not the gold. Just like with sterling silver. There will not
be ANY gold ions at all in the pickle, no matter how much gold you
pickle in it.
I’d guess, Charles, that your pickle was just getting too full of
copper, or had been contaminated with something else, perhaps iron,
tin, zinc, etc. Some gold alloys contain a bit of zinc, and white
golds may have nickel, and both of these would get traces into the
pickle in those cases. Gold itself couldn’t have been giving your
silver that yellow look. But whatever the cause, changing the pickle
for new would eliminate any contaminant causing problems.