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Process | Gumphoto


I’ve been using the “Gumphoto” moniker now for almost 15 years.  Back then, it pretty much summed up everything I did.   Lately I’ve been using casein and fish glue and other things, so a more accurate phrase would be “DichomatedColloidPhoto”.  But I think I’ll stick to GumPhoto.  It isn’t “pretty”, but it fits me.  Like an old shoe.


Most of the  photographs on this site were made using the gum bichromate process – one of the oldest of photographic processes.  Each is a unique work and could never be duplicated.  Unlike conventional color photographs, these photographs are fully archival even when exposed routinely to high levels of light.

In 1839 Mungo Ponton discovered that paper that had been immersed in a solution of a chromium salt would change color after being dried and exposed to light.  It was soon discovered that organic colloids such as albumen, gelatin, casein, and various glues would be rendered insoluble if they were exposed to light after having been mixed with one of these salts.   In my work the salt is potassium dichromate and the colloids used is gum Arabic, which is extracted from the sap of the Gum Acacia tree, and casein.  Gum Arabic is frequently used in the cosmetic and food industries as a thickener, and is the  “gum” component of a gum drop.  Casein is a milk solid.

A mixture of the colloid, potassium dichromate, and watercolor pigment is applied to a surface under ordinary room light. Paper is the most common surface, but I have used aluminum, steel, tile, shower curtains – even the door off of an old Kelvinator refrigerator.  After the emulsion dries it is easily dissolved in water.  But exposure to light will harden the emulsion in proportion to the amount of light it receives.  A negative is placed over the emulsion-coated surface, and it is placed outdoors in sunlight, or under an ultraviolet-rich light source such as a mercury vapor light or a bank of florescent tubes.  After an exposure of a few minutes, the print is simply placed in a tray of water.  In a few minutes, the portions of the photograph that received less light will begin to dissolve and float away.  The work is plucked out of the water when a desired effect is obtained, washed, and allowed to dry.  This process is repeated until the work declares it is finished.  For my work, this usually means six to ten coats of emulsion.  For each successive exposure, the negative must be perfectly registered with the image on the surface of the print.


The gum bichromate process demands an amount of light far greater than could be obtained with a conventional photographic enlarger.  The advantage to this is that gum printing can be performed in ordinary room light, or even-out-of doors (in the shade).  The disadvantage is that negatives the exact size of the final print are required, for this is a “contact” process.   These large negatives are made in the darkroom, using “lith” film – a product produced for the printing industry – and developed conventionally in the manner one would use in creating a typical black and white photograph.  For the monochrome photographs, I usually use one or two negatives.  The full color images require four negatives: one black and white negative each for Cyan, Magenta, Yellow, and Black components of the original image.   As some of the examples on this website will attest, gum is capable of rendering photographs that are every bit as vivid, sharp, and accurate as a conventional photograph.


By most photographic standards, this is a slow and demanding process.  Apply emulsion – wait for it to dry.  Next wait for the exposure. Wait further for the development.  Wait patiently for the surface to dry, so that the whole process can begin again.  Most of all, wait for a lucky break that allows magic to happen.  It often takes weeks to complete a photograph, and the process is fraught with opportunities for disaster.  The success ratio of works started to works successfully completed is often dismal.

I have experimented with many of the historic, so-called “alternative” processes, and they all have their own special charms.  But it is gum printing that has captured my heart.   Its inconsistent nature is both frustrating and invigorating.  Initially, my aim was to tame and control – to use the process to achieve my intended goals.  But gradually I have learned that I obtain better results when I follow the random twists and turns.   I depend upon the serendipitous and temperamental nature of the gum process.  


© Copyright Gumphoto - Keith Gerling