William A Foster. Bromoil, Oilpigment, GumBichromate, Fresson.

This very early photographic printing process was pioneered by a John Pouncy about 1858, not long after the discovery of the negative-positive Calotype printing process originated by Fox -Talbot around 1840 using silver compounds.

The Gum printing process does not use these silver compounds,but used elemental Carbon in the form of a pigment combined with a solution of Gum Arabic and sensitised to daylight or other actinic light source,by the addition of a Bichromate solution,this mixture is then coated onto a stout paper support,dried in the dark,then with a negative in contact,exposed to the light,the image then developed out in a plain water bath,the exposed gum coating dissolving away in the proportion to the light exposed through the negative in use.

Being a contact printing process,a negative the size of the final print is necessary,and can be produced in a variety of methods from smaller sized originals,a final image will require several coatings and printings to achieve the range of tonalities that the artist might require to secure the desired effect.These final images, on a strong art paper support,with fine carbon pigment, are considered to be a very permanent pigmentary method in use,other than possibly prints from Bromoil Transfer methods.As in both cases there is virtually no colloid remaining in the final finished print,unlike the considerable gelatine content in the silver -gelatine print and other processes based on the gelatine layer systems,as in Carbon transfer,Fresson,Bromoil and Oil methods without a final image transfer to a fine paper support.

A difficulty with any gelatine based system is that unless the relative humidity for the display and methods of storage, is kept at a low enough ambient level, gelatine is easily attacked by a variety of fungal and bacterial growths which can rapidly destroy the gelatine within the layers,and thus the permanence of the print can be degraded and possibly totally ruined. With the Gum process however the residual gum in the final print is so low in the case of the Gum bichromate print and in any event so degraded by the bichromate compounds used as sensitiser,as to be inert to the usual range of print infection problems,in the case of Bromoil Transfer,choice of a non gelatine sized final support paper should secure the finest possible permanence as the image thus remains only as ink on paper.

Significant skills are necessary to produce these Gum prints in large sizes,say 20x16 inches,such as in the hand coating of the paper,correct exposures to actinic light sources and in the final water bath method of developing the exposed prints.It is for these many reasons that no two Gum prints from the same negative are exactly alike,as with conventional silver printing, so each print must be viewed as an individual work of Art, as is the case with single copper plate etching and other similar intaglio hand printing methods.

Many original Gum bichromate prints from the late 1800’s, exist in several of the various archival collections throughout the country,and from recent examples viewed by the author,have not suffered any of the deleterious effects of pollution and staining that to which many of the silver gelatine prints are often so prone,as with all pictures in any medium once the base paper degrades,image quality is quickly destroyed.