I've checked and you're right it's not related to purity.
It seems that hydrogen sulfide is responsible for silver tranishing.
after wikipedia:
I'd say though that silver/ silver plated jack would not tranish (unless exposed to H2S deliberately), because pluging in and out would have polishing effect. But that's just my blind guess
Edited by piotrus-g - 2/14/12 at 5:12pm










