I agree that you better be very careful before attempting to clean old clay chips. Having offered that warning, here is what I do when I feel I must clean chips:

1. A pencil eraser is good for removing scuffs and crud from old chips, although I wouldn't want to tackle a full rack of 100 with just me and a pencil.

2. After trying about every possible cleaning agent, I've settled on "Quick'nBrite", an all natural, non-detergent pink paste you see offered on TV and at fairs and flea markets and so forth. They also have a web site.

The trick seems to be to find something that will dissolve the greasy deposits that accumulate on well used chips, without removing any ink, or leeching moisture from the chip. Quick'n'Brite is a thick paste, and does not seem to encourage any moisture transfer, while doing an excellent job of breaking down the greasy gunk. I just stick the chip in the bucket edgewise, rotate it a few time to coat the chip thoroughly, wait about 15-30 seconds, then wipe the chip down with a washcloth. It's revolting how dirty that washcloth gets after only a few chips.

Another good wipe with a clean rag to remove any trace of the Quick'n'Brite, and you're done. I've never ruined a chip this way. I did ruin a batch of old clays once by putting them in the washing machine with bleach and Tide, it messed them up pretty bad and was very loud to boot. But the fragments were sparkly clean!