Layers

You don't necessarily have to do a multi-layered print but it is an option but before painting the surface with the gum bichromate solution, you will want to check the size of your negative or digital negative compared to the paper. This way you can thoroughly cover the necessary area for a well exposed image. You may also want to be sure that your paper is sized to your specifications, so if you are doing multiple layers, the paper won't shrink after drying.

Mixing the chemistry for one layer or a particular color will vary on the concentration of potassium (or ammonium) dichromate, freshness of the gum arabic and the brand of water color used. The book of Alternative Photographic Processes has a good starting point for mixing up the chemistry for first time users of the gum bichromate process.

After mixing, pour the solution across your paper and bush it evenly across the surface. Be sure to not overbrush because that can fray the surface. Place on a rack to dry and when it is no longer cool to the touch, you may expose your image onto the paper via the sun or a UV light box.