Oxidizing finished sterling silver chains

Just curious if anyone had any thoughts about applying patina on a
finished chain (purchased)? I have some heavy snake and other various
chains (typically high quality Italian) that I’d like to oxidize, but
I don’t want to ruin them in the process. So tips anyone? I am
worried about coatings or even rhodium type or fine silver plate that
maybe applied on top of the sterling that would make the patina
process a problem.

Thanks!
Kay Cummins