Houdoy's Process 1858
The paper is floated upon a lukewarm solution of gelatine at 5:100, and
when dry, on a bath of uranium at 10 or 15 per 100 of water. After
exposure to the sun the image is developed with a solution of silver
nitrate acidified with acetic acid. The exposure varies, according to the
nature of the negative, from one to ten minutes; it must be long enough
for the image being developed in from thirty to forty seconds. It is then
removed from the silver bath and placed in the following:
Ferrous sulphate 3 to 8 parts
Acetic acid 2 parts
Water 100 parts
In this bath the image takes a great vigor and appears entirely on the
surface of the paper. When the proof has been too long exposed it should
be washed slightly before placing it in the iron bath. Developed, the
image is, generally, of a sepia tone, which can be turned to black by a
solution of chloride of gold, 1:1,000, washing afterwards as usual.