This
is a process that was patented by the Neue Photographische Gesellschaft
in 1908. Casein, the main protein in milk, can be used in combination
with a dye or pigment and potassium dichromate to make prints. (Other
types of fatty material can be used as well.) Casein is soluble
in alkalis and organic acids. It is obtained from milk by acidification
and is often known as 'curds'. It was introduced as a medium for
silver salts in printing out paper.
Take
100 ml of full fat milk and add to this 7ml of acetic acid. After
the curds have formed, strain through a cheesecloth and rinse until
the acid smell disappears.
Drain
the curds and then crumble into 55ml of 1% ammonia and leave for
2-3 hours. Add 100ml of water and the Casein is ready for the pigment
to be added and then sensitised using the formula below.
This
solution can also be refrigerated to be used later. Mix equal parts
pigment/dye and sensitising solutions immediately prior to use.
Dye
Formula:
Casein solution 100ml
Watercolour pigmented water 100ml
Sensitising
Formula:
Potassium dichromate 25g
Water to make 100ml
Place
the negative to be 'printed' in contact with the coated paper and
expose to a UV light source.
Soak
the print in cold water until the unexposed dye areas begin to detach,
and then transfer it to a cold water bath containing ammonia. After
a few minutes, hold the print upright and gently spray with fine
flow of water, then re-soak in the ammonia bath. Repeat spraying
and soaking until desired result is obtained.
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