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Processes - Gum Bichromate

Gum Bichromate Process Popular: 1894 to 1920s Discovery Mungo Pontin discovered the theory of the process and experimented with gum printing in 1839. However the process was not introduced more widely until 1894. It remained popular until the 1920s, but is still practiced by some enthusiasts today. Process 1. Dissolve gum arabic in water and mix it with a pigment and a solution of potassium bichromate or ammonium bichromate. 2. Coat this solution evenly onto a sheet of paper, and allow the paper to dry. 3. Lay a negative on the paper, and expose to sunlight or ultra violet light. The surface will harden in proportion to the amount of light that it receives. 4. Lay the print in water and allow the softer surfaces to be washed away, leaving colour in the highlights. In order to achieve more satisfying results, the photographer sometimes repeated the process above, using the same sheet of paper, but a different colour of pigment, exposing either the whole negative or chosen parts of it to the new colour. In doing this it is important to ensure the negative is placed in exactly the same position over the paper for each exposure. Result The gum bicarbonate process was popular for the creative control that it gave photographers over the final result - both through the possible use of more than one pigment and in the ability to control the amount of pigment left on the paper at step 4 above using a brush or by directing the water flow. In Edinburgh Mungo Pontin who discovered the gum printing process was the Secretary of the Royal Bank of Scotland in Edinburgh. Today See Terry King's 'Hands on Pictures' web site for news of photographers using the process today. In December 2003, members of the Scottish Society for the History of Photography visited Hospitalfield House, Arbroath, Scotland, and saw some experiments that had been carried out in early photographic processes by Norma Thallon, Artist in Residence, including the gum bicarbonate print below: © 1. Some of the details above are based on information in the book: Looking at Photographers - A Guide to Technical Terms (Gordon Baldwin) 2. Terry King's 'Hands on Pictures' web site gives further details on the process and for some examples of gum bichromate prints.


The Gum Bichromate print is different than the other processes in that the sensitive emulsion offers a base that a dye or water pigment can be added to produce any colour print the maker requires. It is also a process that allows re-coating the paper support several times using a different colour emulsion for each coat.


Sensitizer: Ammonium or Potassium Bichromate 30gr. (Ammonium is a more expensive and is a more dangerous chemical to work with but reduces the exposure time by half).
Add 75 ml heated distilled water and dissolve by stirring.

Add cold distilled water to make 100ml.

The sensitizer solution can be stored for a few months and is not light sensitive until mixed with the gum. (Being a saturated solution, this can crystallize out but can be re-dissolved in a warm water bath.

Gum: Mix 30gr Gum Arabic dissolved in 180ml distilled water. Let this mixture stand for a few days until completely dissolved. If gum arabic in lump form is used, strain off debris. The gum should have a syrup-like consistency. To prevent bacterial or fungoid growth from forming add 0.40 to 0.60 gr of Mercuric Chloride to this mixture.

Pigments: Use only the best quality water colours in tubes with good pigment saturation to achieve a photographic quality. Dry powder pigments can also be used with good effect.

1. Under white light mix 10ml of gum with a 2-4cm "worm' of water colour from the selected tube.
2. In subdued or dark red safe light add equal amounts of sensitizer and gum solution. Note that the colour will have changed with the addition of the orange sensitizer, but will return to the original colour after development.

3. Brush mixture onto paper with vigorous strokes. Aeration by brushing will assist in setting of mixture and avoid the tendency of the gum to "fish eye". For a photographic rendition, use a soft blending brush to finish the application. Once mixed, the mixture goes off, so mix only small amounts at one time.

4. Dry as mentioned in the Cyanotype process.

5. Once dry, expose by contact printing explained in the Cyanotype process. Exposure in sunlight should take about 3 to 6 mins.

6. Development procedure will take approximately 1hr and can be carried out in white light. Several trays of water are required, and the temperature of the water must be kept between 25-26 degrees. The tray is changed at 15min intervals. Insert print face up in first tray for about 1 min until wet and uncurled. Gently turn print over and leave to float in the water. Sliding the print gently in and out of water face up will speed up the development. Rocking the tray will cause streaks on the print. Gum with pigment hardened by the sun will adhere to the paper while non -hardened gum will dissolve with the pigment and sensitizer.

A fine jet of water can be applied to highlight areas to bring out a little more detail in these areas. Development is finished when all unhardened gum and sensitizer is dissolved. Underexposure is indicated by flaking off of the gum. Over exposure is indicated by delayed development time. Slight over exposure will yield acceptable results. NB: When using Lamp Black pigment, print must be slid continuously in and out of water. If this is not done the pigment, being lighter than water, will re-deposit on the print.

7. Dry the print as described for the Cyanotype. If application of several colours is desired, follow steps 1-7 each time. The print must be well dried before commencing the next coating. When printing several colours in sequence and using the same negative, use Opaque Red to mask off areas on the negative that you wish not to print with the next colour.Make sure that you paint this on the film base not the emulsion side of your negative.

With this process it is best to wipe all surfaces when the chemical mixture is wet as some pigments can stain and be difficult to remove.


Email questions:

Greetings LLoyd,

I have read your article regarding the gum bichromate process (alternative photo site )and have a couple of questions I was hoping you could answer:

I would like to use powdered carbon as a pigment in the gum process. Any idea as to how I should/could prepare the pigment (mix with glycerin, starch, etc.)?

How should the paper be sized initially before coating? Gelatine? Arrowroot starch?

I appreciate your time and thank you for your expertise!

My best, Ken

Hi Ken,

Thanks for you email,

I have done this about 1986 and it worked quite well - Pigments produce wonderfully rich prints so I know it works. I’m not sure on the size but I have the feeling it was a starch mixture. Different paper requires different treatments. One thing I would suggest is to expose it in diffuse light rather than bright sunlight. Also you might find you don’t need to add quite as much pigment as you would water colour paint. If you can track down the used cartridges from a high quality digital pigment printer you might be able to get a bit of spare pigment of different colours.

Keep experimenting and write down what you are doing. Its so easy to lose track of where you have been. Let me know how you get on.

Cheers Lloyd



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