a pressure washer might help flake the remaining coating off.. and do the least scratching of the metal underneath...if it's at all flakng underneath it will lift it.. work from the edge > to inside.. a 400 grit sandpaper will give close to a mirror urface... andd I got some cream at a motorcycle show that could polish an aluminum can to a mirror finish...but not withoout a bunch of rubbing...
A big buffing wheel would make the ball shine.. and wear away the remainig coating
