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Gum Bichromate in a few words

Updated: Jan 18, 2023

Gum Bichromate is a contact printing method invented in 1855. Compared to other contact printing methods like cyanotype and platinum palladium, gum bichromate is unique in its ability to add pigment! This feature allows it to be compared more to printmaking processes like screen printing.

Betty Hahn, My Sisters-Negative and Positive, 1965

2 color gum bichromate print on paper

Once you have your emulsion mixed, coat your paper in your dim room, you can expose your emulsion to a small amount of light, so long as it isn’t exposed to UV light (that means keep it indoors until you are ready to expose!)

You can expose your work in an exposure unit or in direct sunlight!

The emulsion is developed in two baths of water, one warm, one room temperature. When you are developing be aware that the emulsion is very soft. Unlike cyanotype, which is soaked into the paper itself, this emulsion sits on top of the paper and is hardened when exposed to light. If you are too rough with your prints some of the emulsion can be rubbed off, this can be a downside or an upside! If you don’t like the way part of your image is developing you can lightly rub the emulsion to encourage it to develop faster!

Once you have your first layer down it’s time to start thinking what your goal is with the image, you can stop at just one layer, but with the freedom of choosing your own pigment a lot of the fun in this process is layering different colours over top of each other! You can create a true to color image using a cmyk process or get wild and come up with your own set ups!

Martina Shenal, Untitled (040807) Gum Bichromate print

Some things to consider:

If you are layering different colours, consider how you plan on registering your images, some folks poke holes in the print and transparencies when setting up, some just eyeball it, so consider what works for you!

Toxicity: Potassium Dichromate is a carcinogenic chemical- be aware of this when using it, it is best to wear gloves and work in a well ventilated space, you may want to consider a mask as well. Be aware of how you dump this chemical, you wouldn’t want to dump it in your garden.

Some helpful resources if you're interested in learning more about the process include Christina Z. Anderson’s book Gum Printing and Jill Enfield’s Guide to Photographic Alternative Processes.

Interested in creating statement darkroom prints? Introducing, Alternative Processes Academy™
The complete course to cover some of the most famous & sustainable alternative processes so you can explore your creativity in more unconventional ways! Happy printing!

Author:Elisa Blobaum Images courtesy of the artists

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