Undamaged (non-rusted, non-pitted) balls can be restored to new using a high
speed bench grinder with a cloth wheel. Use stainless steel or chrome
jeweler's rouge. Get the green stuff in a tube, not the brick. Gem shops
will have the cloth wheels and rouge. Be sure to wear safety glasses, dust
mask, and heavy gloves.
Apply rouge to the wheel often. Avoid pressing the ball into the wheel--let
the rouge do the work. This should only take a couple of minutes.
Note: This also works great for polishing the heads of your front leg bolts!
Tim Arnold pinGame journal, #25 September 1993 pp 34.