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Lloyd Godman
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.
http://www.edinphoto.org.uk/1/1_early_photography_-_processes.htm
GUM BICHROMATE
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.
Recipe:
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.
Method:
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
http://www.livick.com/method/gum/pg1.htm
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