Gum bichromate is a 19th-century photographic printing process based on the light sensitivity of dichromates. It is capable of rendering painterly images from photographic negatives. Gum printing is traditionally a multi-layered printing process, but satisfactory results may be obtained from a single pass.

Gum bichromate (or dichromate) printing involves creating a working emulsion made of three components:

-Gum arabic

-A dichromate (usually ammonium or potassium)

-Pigment

The emulsion is spread on a support, such as paper, and allowed to dry. A negative or matrix is then laid over top the emulsion and exposed to a UV light source. Usually a contact printing device or a sheet of heavy glass to ensure even, constant contact is employed. The light source will harden the dichromate in proportion to the densities of your negative. After exposure, the paper is placed in a series of plain water baths and allowed to develop until the unhardened portions of the emulsion have dissipated.

As I wanted a chromatic print, the artwork was split into it's CMYK CHANNELS in Photoshop and each channel inverted (negatives). These were then printed on OHP sheets of the desired size and named as their respective channels.

i)   A Potassium dichromate solution was prepared in 1:8 ratio i.e., 1 part of Potassium             dichromate crystals and 8 parts of distilled water. This was stored in a bottle in a dark         place. (Do not let this solution get exposed to UV light)

ii)  Gum arabic solution (Daler Rowney) and water colours of the CMYK were kept ready.

i)  An acid free paper was cut to the desired size.

ii) The potassium dichromate solution and Gum arabic were mixed in a 1:1 ratio to which was added the first water colour paint of the CMYK (Yellow). This formed the emulsion for application. (Usually 4 cms of paint is sufficient for an A4 size print.)

Note: The Dichromate and gum should NEVER be mixed earlier and kept. Only mix it just before the application.

iii) A thin coat of the Yellow emulsion was applied to the paper and kept to dry in a dark place

The yellow channel negative was placed over the emulsioned paper and exposed to direct sunlight for a timeframe between 3-10 minutes. 

A glass was kept on top of the paper to assure constant contact.

The light hardened the dichromate in relation to the densities of the negative, and as it hardened the gum caused it to stick to the paper. This would stay on the paper later during washing while the unhardened parts would wash off.

The paper was rinsed in running water for 5 minutes and then left in a tray of clean water for 40 minutes. The unexposed unhardened emulsion washed off and a brush was used to rinse off the detailed parts, if required. The image was seen forming in yellow. It was then left to dry completely.

THE STEPS 3 TO 5 WERE REPEATED THREE MORE TIMES (With other CMYK channels i.e. in Magenta, Cyan and lastly Black) AND THE CHROMATIC PRINT WAS DEVELOPED.

A lot of trials and errors determined the correct exposure that was needed.

Too much exposure led to too much hardening and the colour would not come off.

Too little exposure led to flaking of the paint of immediately in wash and no image would develop.

Every image was tested for the perfect exposure it would need in miniature test versions.

Different print results during trials and experimentation.

Pages from an illustrated book by me, showing the original illustrations and the results after the gum bichromate print.

See the entire illustrated book : ' The love song of J. Alfred Prufrock '