I've developed direct positive paper with caffenol in order to get a nice sepia tone. In my experience, caffenol smells terrible. If you do decide to experiment

I've developed direct positive paper with caffenol in order to get a nice sepia tone. In my experience, caffenol smells terrible. If you do decide to experiment with it (and you should) I would recommend getting the absolute cheapest instant coffee you can find. The acid in robusto beans helps the reaction along. If you're looking for a non-toxic commercial developer, Kodak's Xtol developer is based on ascorbic acid.