Boy! Dejavu. When I started chipping, this was one of my questions. I picked up Sterling Magic, which was forumulated specifically to clean chips (at least that's what I read) but now seems to clean everything else very well. I use a tooth brush and some magic. Careful with the hot stamped chips, you might not want to bruch too hard. Also I advise on drying your chips immediately.

Cheques in the mail and CT Rodgers sell Magic.

Good luck, cleaning can bring out a lot of detail and color in a chip.