Cleaning old chips may not be a good idea. If the chips are worn, cleaning them will give them an "unnatural" appearance and lessen their value. You also have to be careful not to damage any part of the chip during the cleaning. If the chips are hot-stamped, particular care is needed during cleaning so that none of the hot stamp is lost. My advice ... if you are not 100% sure of what you are doing, don't clean them.

If you are selling the chips, let the buyer decide if the chips are to be cleaned. If you are just cleaning them for yourself, you can use water, dish washing detergent (the milder the better) and a toothbrush.