I've run my balls through a tumbler.
(Pachkino balls, that is!)
I used a Berry Mfg. tumbler with some Flintz metal polish and the supplied corn media (I hear walnut media is better for tough polish jobs)
Anyway, the balls came out quite nice - not quite as shiny as brand new pachinko balls, but pretty close.
I've also used my tumbler to polish my BYOAC brass tokens - does a fantastic job, they come out looking brand new again.
Kevin