Pickle chemistry

Hey, there everyone!

I have this little phenomenon happening at my hot table. I know how
to resolve it, but I would like to know why it’s happening.

I have been using the rio pickle, warmed in an oversized crockpot.
Works great. Eventually the pickle will evaporate, go blue-green as
it becomes saturated with copper oxides, and when there really is
almost none left, I will neutralize with sodium bicarbonate (baking
soda) and dump it. About the same time, I’ll freshen up the soda bath
I use for metal coming out of the pickle, to neutralize.

Sometimes, not with every pickle batch/soda bath over the years, but
maybe three times, when the pickle is old and nearing the day when I
say, “hmm, think I’ll change the pickle today,” this weird thing
happens. Sterling, after soldering, goes in, looks fine, cleans up to
a white, but then goes instantly to putrid yellow when it goes into
the soda bath after the pickle. Chemically speaking, why?

My response to this problem has been to change the pickle and soda
bath… problem solved. But curious minds want to know… what’s
going on here?

Thanks in advance for your genius!