Terms searched: "history of sex toys" + "cock rings", castration + "cock ring" - I've never searched for something like this before, so if you've got any pointers they're welcome as well. :)
1. How early would cock rings have been known about in Europe? It doesn't matter if they were taboo, or not (though of course I presume they would be) - I'm writing historical smut wherein one of the characters is a time traveller, so any inhibitions that might be present at a given time wouldn't bother him in this regard. Really, I'm wondering when they'd go from something completely unknown to at least something people would gasp in disapproval of. XD
2. When my time traveler gets to the eighteenth century, he ends up in a relationship with a castrato, who finds the ring from the previous question among the time traveler's bag of goodies. He, well, liberates it for his own purposes - but how would this work? Would it be approximately the same? All I could find on the internet talked about using the rings for castrating oneself, which, um, is definitely not the direction I had expected.