Here are the rules as I know them for Artist Trading Cards:
1. They must be 2 1/2″ x 3 1/2″ in size.
That’s it. Anything else goes. The deal is to make small pieces of artwork to trade with other people, while letting your imagination run wild. Wonderfully open-ended, and small enough so you can experiment with TONS of different materials and techniques easily.
You can make your own cards or buy them pre-made at art stores, or on Amazon. (You can also use playing cards, which are the same size.)
Usually they’re more than a simple sketch, and can be really beautiful pieces of art. They don’t have to be made with traditional materials- I’ve seen some on polymer clay, metal, and wood. Cool.
If you like, you can seal the finished card with acrylic medium or Mod Podge, and the back is usually finished simply and labeled with basic info, like the artist’s name, email, date, and perhaps the name of the swap if it was an organized one.
Catslife Press has a super collection of Artist Trading Card rubber stamps for the backs of the cards.
I found two kid-specific ATC sites with more information covering the history, techniques, and swaps:
Atcsjr.com- All for kids who want a place to trade.
Student ATC- This free site helps teachers organize classroom to classroom swaps.
As far as how to store your collection, the size fits into standard baseball card storage sleeves. I found Your ATC Store that sells pretty much everything you could possibly want in regard to ATC’s, including plastic sleeves, envelopes, pockets, albums, boxes, and all sorts of other items.
Following are some links to even more ATC stuff! This book looks extremely inspiring, and you can also buy an introductory kit for making cards. I smell a Christmas present coming on…