Plastic ring found on a walk, 10 pt. diamond. I know it doesn't look like a real diamond in the pic but it is, and it's a pretty good quality stone. I set it with rubber cement, didn't have the nerve to use epoxy.
I've been playing around with some polyolefin heat shrink tubing for electronics that I picked up at Home Depot this weekend. This stuff has great possibilities, but I have no idea if it is safe. Once it shrinks it's really on there. It's very flexible and is supposed to take abrasion well. Tonight I incorprated the tubing with an adjustable depletion gilded sterling silver ring.