One of my other hobbies is restoring and collecting old pinball machines. One of the first things to get upgraded are the actual pinballs. They are an inch and a sixteenth (1.0625") in diameter and are hard polished steel. I think that they could be excellent tools to polish the crowns if used with the correct compounds. I now have 11 pinball machines and dozens of used pinballs. If anyone would like to try a couple, drop me a note and I'll send you some.