I think that the major concern is with chips that have been altered in some fashion so that are no longer what they appear to be. If you are justing cleaning a chip, in effect you are removing something that was not originally there ... the dirt. I do not view this as an alteration. Care must be taken in the cleaning so that anything that was originally on the chip is not damaged.

A non-original chip is one that has been altered in some fashion so that the chip is something other than that was originally manufactured. If you are filling a hole or a crack than you are adding something to the chip that is not original. If you even replacing an damaged or worn inlay with one from another chip, that is an alteration. If the casino cancels a chip with a hole, notch or hot stamp, that is an OK alteration, because the casino is doing it. It is not OK if anyone but the casino or the manufacturer does the cancellation.

Basically any alteration to a casino chip should be disclosed prior to a transaction. When buying or trading casino chips, you should be able to assume that the casino chip is "original", unless told otherwise. I personally believe that casino chips should never be altered, with the only exception of cleaning.