For one of our last alternative processes, we will learn the technique of gum bichromate printing, or "gum" printing as it's often known. Gum printing is one the earliest color photographic process, invented by efforts of William Fox Talbot (who invented the first paper negative) and Mongo Ponton. Essentially, when a metallic dichromate (such as potassium) is combined with a colloid (a large moleculed gel or emulsion) like gum arabic, it becomes UV light sensitive and hardens proportionally to the amount of light striking it.
Unlike any of the other alternative processes, gum printing can be any color, because the gum arabic that's mixed with the dichromate can be tinted with watercolor. Layering multiple hues of color can create even create the illusion of a full-color image! (we'll talk about how Photoshop can be used to "split" a color image into three color spectrums and three different negatives to make a full-color bichromate print!)
While you are shooting your independent series, we will experiment with gum printing in class. To begin, create 2 new 5x7 ortho-litho negatives with which you can contact print with. You will need more than one to be able to layer imagery. Then, you can size and tone your paper with the dichromate solution to print with.
Here are two fantastic websites that explain the process and history of gum bichromate printing far better than I can:
Be sure to check out the Flickr group "Gum Bichromate" here to see a ton of examples of this printing process. You can also check out the simple slideshow below:
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