Photographic Printing, How to Create a Real Gum Print
How to Make a Real Gum Print
Gum bichromate, now known as gum dichromate, is one of the earliest examples of modern photography. Mungo Ponton, 180 years ago, in 1839, found that bichromates are light sensitive. A little later, William Henry Fox Talbot discovered that bichromates, mixed with the colloids, gelatine or gum arabic, once exposed to light, are insoluble in water in proportion to the exposure received. However, it wasn’t until 1855 that Alphonse Poitevin had a flash of inspiration and added ground carbon black to the mixture to create the first carbon print. John Pouncy, in 1858, added coloured pigments and so extended the range of coloured photographic images from the rich yellow and brown tints of salt prints and egg albumen, and the Prussian blue of cyanotype.
Early gum prints were usually monochrome, or, pigments laid over cyanotype or platinum prints to strengthen the shadow areas. Monochrome prints have no problems, paint your mixture on the chosen paper, expose to the sun or other UV source under an appropriately sized negative, develop and fix, much the same as a cyanotype or salt print.
When we want to combine with other processes, the problem of registration raises its awkward head, you have to make your first print, develop and wash appropriate to the type, then re-fix your negative in registration for subsequent exposures with the gum mixture.
The earliest method of registration was pins; just make sure you get back in the same holes each time. I use a piece of folded card, a window cut in one side to allow light through the negative and a square cut L of card glued on the opposite side to set the coated paper for each operation. I am principally a monochrome worker and that is what this how-to is about, when you can do this, you will easily work out the problems of registration; you can only learn it by doing.
Like the cyanotype process, gum printing is cheap and easy; but is not as safe.
POTASSIUM DICHROMATE IS TOXIC
Remember the safety precautions with chemicals, rubber gloves, goggles, don’t get chemicals in your mouth, wash your hands, don’t work on food preparation surfaces; don’t eat, drink or smoke whilst using chemicals, most importantly:
it is definitely not for children.
The whole operation of mixing the potassium dichromate and coating the paper is carried out under normal tungsten lighting or daylight with the room curtains closed, no fluorescent tubes or CRT TV light.
Mix 5gm of Potassium dichromate with 100ml of warm water, use a 250ml brown bottle, screwed down cap, so you can shake it to ensure it is completely dissolved. In a small saucer, never again to be used for food purposes, squeeze out a pea sized amount of artist watercolour and mix with a teaspoon of glue, ordinary PVA glue will do. I use gum Arabic because I’m a water colourist and use it anyway, ad to this a teaspoon of the potassium dichromate you mixed. Brush on to the paper, don’t panic at the bright orange mixture, it will wash out during developing, and dry with a hair dryer, then tape to it, along one edge, your negative, sandwich this between a piece of hardboard and a sheet of glass, fixing with bulldog clips.
Like cyanotype, gum printing is a contact print process, so the main disadvantage is obtaining large enough negatives. I use a 5x4 film camera and contact print from the negatives it produces. If you have a 35mm or medium format camera, you will need to scan, or get scanned, the negatives to print out large negatives on overhead projection film (OHP). If you have a digital camera, the chances are you already have image editing software on your computer to create negatives with OHP film. It is possible to make negatives on ordinary writing paper, Talbot made his by putting sensitised paper into his camera, of course, we use an inkjet printer to print our scanned neg. The negative for gum printing needs to be low contrast
Put in the sun, or in front of a UV light source, and check by unclipping and lifting your negative, say, every three minutes until the tones look right.
Wash/develop the print under warm water until the image appears to be fairly clear, this is all a matter of taste and experience, learning by doing, gum printing is akin to painting and is subjective, to get a strong colour you may need to repeat the process.
Wash for half an hour, if you really fall in love with your print, give it an archival wash in a potassium metabisulphite solution, in a well ventilated room, about 250gm in a litre of water for about 5 minutes.
Like cyanotype, salt prints are as permanent as the support the are printed on, any good quality, sized watercolour paper will do, I use Saunders Waterford, 140 lb, hot pressed or NOT (cold pressed).
I have no control over how you may carry out these operations, as I said earlier, it is not for children and potassium dichromate is a toxic chemical, you are responsible for your own safety.