Hi Janet,
your original post interested me, so I googled for the chemical composition of sweat. There were some useful answers, with actual values of individual chemicals, with the qualification that the specific composition depends on the individual’s chemistry.
Next I searched for metals turning fingers green, the answers referred mainly to copper, tho in sweat analysis many other metals were mentioned.
Re rings containing copper, ie standard sterling, in the moist saline oxidising conditions between finger rings and skin, anything can happen! despite there being only 7.5% copper therein.
I didnt find anything more specific than the above.
Surprisingly no guesses tho.
Ted…