Here are a couple of ATCs which I made from a deck of playing cards. Firstly I coated the cards lightly in gesso. I still wanted the card markings and background to show through so I wasn't to particular with making this an even coat. I then basically collected all my red and black scraps and decorated at random. I printed out little sticky labels with the usual ATC info, and placed these on the back of the cards. Mind you which was front and which was back varied often. I was really happy with how they turned out, and I think their recipients liked them too.