Just like the silver/gold/mithril ones we have now? Actually, this is a pretty neat idea for cosmetics, but if they are added, you know that someone is just gonna be all like: "YAY HE FINALLY ADDED MO' RINGS!!!! DO THEY HAVE POWERS???? I CANT WAIT!!" Get my drift? I would appreciate having rings for all the metals though. Good idea.
That's a neat idea. Rings, and objects like them exist in most cultures and it makes sense that they would make them out of the materials they use to produce other metal works. And even if it would'nt make much sense to make a ring out of some metals, such as black uruk steel, I think the player should still have the ability to do so.