Gum bichromate was one of the first photographic printing processes. The light sensitive emulsion is made with a super-saturated concentration of potassium bichromate, guar gum and watercolor pigments. It is then brushed onto pre-shrunk printmakers paper (100% rag content). After it dries, a negative is placed onto the emulsion and exposed under high intensity light. It is then bathed in a warm water bath about an hour and hung to dry. The photos in my gum bichromate portfolio are of negatives that were posterized. The original 35mm negatives were enlarged onto 4" X 5" high contrast film using 3 different exposures making positive images. Those images were again enlarged (or contact printed depending on the size of the final image) to make negatives. Each of the prints was created exposing each negative in registration with a different colored emulsion. It is very labor intensive. Nobody does it anymore.