Yet another use for Mr. Clean Magic Erasers. As you can see, these balls, which are part of the backglass animation for my 1962 Gottlieb Rack-A-Ball, were pretty dirty. I left a pair of them uncleaned for reference (the ones on the ends). The balls in the middle where cleaned with a little warm water and gentle rubbing with a magic eraser. The difference is incredible. Other RGP posters have had good success with Scotch-Brite pads too.