It's probably not worth much, whatever it is, if it's that badly worn/corroded, but if you want to see if you can bring anything out, try soaking it in acetone overnight, rinse under hot water, and blot dry with a paper towel. It may take a few tries before you get any results, but sounds like you don't have much to lose. If there is a particularly stubborn area, you can also soak a q-tip in some of the acetone and work on it gently with that.


















