Follow this link to the site for antique poker chips:

http://www.antiquepokerchips.com

I'm not sure how much more "clay" is in antique poker chips of this sort than more modern "clay" chips, such as those made by Burt Co. and its successors, but the best place to learn about them is to look at that site and get to know the serious collectors. I'm sure they can help you learn a lot about them.

Michael Siskin