A Poitevin's Process 1870

"I use a paper prepared with iron sesquioxide rendered sensitive to light

by tartaric or, better, citric acid in concentrated solution. This paper,

after desiccation and exposure to light, possesses the property of

reducing the solution of silver nitrate and that of chloride of gold, and

of turning blue with a solution of potassium ferncyanate in the parts

where light has reduced the iron sesquichloride into the oxide at the


"To coat the paper with an equal layer of iron sesqnioxide, I brush it

with a tuft of fine linen dipped in a solution of iron perchloride at 10

or 12 per cent. of water, and dry the sheets in the dark. I immerse

afterwards these sheets, one after the other, in a tray containing aqueous

ammonia, in such a manner as to well wet each sheet successively. A

sufficient number of sheets being immersed, I pour off the ammonia in a

vial, and, in the tray, I wash them several times, and remove them one by

one to hang them up to dry, even in full light, the iron sesquioxide not

being sensitive to light."

"The paper can be prepared in quantities beforehand. To use it I apply

upon each sheet a solution of citric acid at 30 or 35 per cent. of

water(44)--which may be done by daylight--and let them dry in the dark."

"Exposed under a negative of the ordinary intensity, the paper is

impressed in sunshine in a few minutes; in the shade it requires about the

same time as chloride of silver paper."

"After exposure the image is not visible, and without being obliged to

shelter it from light, I immerse the print in a solution containing about

1 per cent. of silver nitrate. This solution can be used over and over

again, by adding to it a little of the silver salt. It does not become

turpid by use; it simply turns slightly green from formation of iron

nitrate. The image appears soon and rapidly becomes vigorous; in half an

hour it will be completely developed. When the exposure is sufficient the

color is deep sepia, but not so intense if the quantity of citric acid is

feeble. No fixing is necessary; it suffices to wash in several changes of


"The image can be toned with great facility by a weak solution of gold or

of platinum chloride, or, better, by a mixture of these two salts. If the

impressed paper be treated by a very diluted solution of potassium

ferrocyanate, one obtains very pretty blue proofs."

"A weak solution of gold chloride develops a violet image. A solution of

platinum chloride has no effect."

"All the various phases of this printing method can be followed in full

(diffused) light; there is only the desiccation of the paper when

sensitized with citric acid, which requires to be done in the dark."