Gum Prints
As early as 1838 the pioneers of photography understood that mixtures of dichromate compounds were light sensitive, but a Frenchman, Alphonse Louis Poitevin, first thought of adding pigment in 1855. The process became popular in the 1890s, and its practitioners called themselves “gummists.” Really.

The chemical formula can be simply stated as:

artist’s watercolor pigment + gum arabic
+
potassium dichromate

This emulsion is brushed onto high quality watercolor paper. After drying, the paper is exposed to ultraviolet light in contact with a negative the same size as the desired final image. The “development” consists of washing in warm water. These prints were made with multiple layers of emulsion registered to each other, exposed and developed in succession.

Questions for the photographer
Q: Is this a photograph?
A: Well, sort of a photograph.
Q: What do you mean, "sort of"? You’re the photographer. Don’t you know?
A: Yes. I started with either a slide from a film camera or a file from a digital camera. On the computer I enlarged the image and printed it as a negative on a piece of clear film. Then I placed it in contact with a color-tinted, light-sensitive emulsion, brushed onto watercolor paper as in the description above. I exposed it to an ultraviolet light source and washed it in water. So they’re also paintings, sort of. Except for making the negative on a computer instead of in a large-format camera, the process is unchanged from the days of its invention
Q: Are they archival?
A: Yes. Many gum prints survive from the earliest days of the method, almost 150 years ago, and they appear to be in perfect condition. Since a gum print consists mostly of the same materials as a standard watercolor painting, it can be expected to last many hundreds of years.
Q: You say that the emulsion is pigment and gum arabic. Doesn’t that mean that basically it’s made of dirt and tree sap?
A: Yes.
Q: Are these prints produced as a numbered, limited edition?
A: No. Although I use the same negative for multiple prints, each print is quite different because the colors, brush strokes and imaged areas are unique to each print. It would be impossible to make any two alike.

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