Ok so for fathers day I bought him a cast iron pan to make individual corn bread pieces. I got it from a flea market for $15.. Not bad at all! Seems to be in awesome condition. The only thing wrong with it, it seems to have some kind of hard black build up in some spots I would like to clean it some how.. Any ideas? ...also... I havent been too good to mine and its started to rust. What should I do about that?