A customer of mine just called to talk to me about a silver necklace which marked a brand-new yellow turtleneck sweater that she bought...
I had this happen to me with a pendant. I could never figure out
whether the jewelry or the fabric was at fault. The easiest cure is
to lacquer the back of the piece. In your case that won’t work, at
least not if it’s the snake chain that’s leaving the stain. I hate
to suggest it, but the best solution may be to have the piece rhodium
Additionally, do you think I'm obliged to offer to pay for the cleaning?
Obliged? No. But it couldn’t hurt as a measure of good will. Did
she suggest it?