Yes, Neil, I have experienced this. Sometimes in the pickle as well.
I've chalked it up to dissolved silver in the solution that plates
out through the solution (the electrolyte) onto the work (the
cathode) due to a galvanic effect generated by the differences in the
potential of the hook or another object. Ammonia seems to hasten
I am not, nor do I claim to be a metallurgist, engineer or chemist.
I leave the science of this to Peter Rowe or Jim Binnion. Just my
Take care, Andy