As in copper plated zinc cent? In my case, that answer is yes. I haven't found one with less than 14k purity however. Maybe if I find one big enough.....
Yes white ( or yellow ) gold rings can read as high as zinc, IF they are big enough. We're talking big fat honking man's rings (like college class ring size).
I don't know about the F75 as I have not used one (past a seller's demonstration). I do find, though, the id (when I use a display) is more apt to register based on the size and shape of the ring, not so much on the metal content. ╦╦Ç
My one experience with this was a tid predicting a zincoln that turned out to be a small Black Hills gold ring. I probably wouldn't have retrieved it, but I'd read that gold rings up as zinc pennies sometimes so decided to retrieve it and bingo gold ring.
luvsdux