Gum Bichromate


Of all the processes I have used, gum bichromate paradoxically holds the most charm for me, yet it has proved to be the most difficult to perfect (to the extent that I am still working on trying to perfect it!) I made my first gum in 1981 (I still have it). But it wasn't until the mid 1990s that I took up the process again seriously. Without the help of the alt-photo list (see LINKS), on which I have 'lurked' for several years, I would not have achieved as much as I have. For those to whom this is new, put very simply gum bichromate relies on the insolubilisation of gum arabic by either potassium of ammonium dichromate when exposed to UV light. Colour is carried in the gum as water colour paint. The final result is basically a water-colour print.


I think that what I like about the process is a combination of its challenging nature, a degree of unpredictability as to the outcome and, above all, just the look of the image.


Snape is a single gum layer in Paynes grey over Cyanotype.


Mayan Stones uses several printings from three separation negatives (shadow, midtone and highlight) in various colours. Recently (eg in Hedges, I have expanded on the use of separation negatives by locally applying different colours of gum before exposure to a specific negative (usually the midtone).


Mannequins uses a rather complex method of reproducing colour (colour the hard way!). Starting with a scan of a colour negative (or more recently a digital file), it is separated into red, green and blue components in Photoshop. Each component is converted to a negative, a Photoshop curve applied which ensures that the tones are correctly reproduced by the process, and then printed: the red channel is printed as a cyanotype, the green channel as a 'magenta' gum bichromate and the blue channel as a yellow gum bichromate - all in register, one on top of each other. Printing like this can often take a couple of days, since each layer has to be done separately. By selecting different pigments for the gum layers it is possible to greatly influence the overall colour of the result. (I agree this is a sketchy description - but there are websites which detail the process so well (see the LINKS page for URLs) that there is little point in my going into much detail here).


Works using Gum Bichromate: