The Black Or Ink Process Ferro-tannate Process

This process gives black positive impressions on white ground from

positive cliches, and negative impressions from negative cliches. It has

been attributed to Mr. Colas, but in reality it was invented by Mr.

Poitevin, who describes it as follows in his communication of May, 1860,

to the Societe Francaise de Photographie:

"I make a solution containing--"

Iron perchloride, cryst 10 parts
Tartaric acid 3 parts

Water 100 parts

"I apply the paper on this mixture and let it dry spontaneously in the

dark, and at the moment of using it I completely desiccate it at a gentle

heat. Thus prepared the paper is of a deep yellow color. Light decolors

it rapidly, and ten or twelve minutes' exposure through a positive cliche

suffices to well impress it, that is, to reduce in the whites the iron

perchloride to the state of protochloride."

"To print, one is guided by the decoloration of the paper, and even for

more facility I add to the solution of iron perchloride and tartaric acid

a small quantity of a solution of potassium sulphocyanide for the purpose

of obtaining a red tint, which is more visible and disappears also under

the influence of light in proportion to the decomposition of the

perchloride. One obtains then after exposure a red design on the white

ground of the paper. This red color is not permanent. It even disappears

by keeping the proof in the dark."

"To develop and then to fix the design thus obtained I wash rapidly the

paper in ordinary water, or better, in water holding chalk in suspension.

The red coloration disappears, a part of the iron perchloride is washed

out, and in the parts which have not been acted on by light the

perchloride is transformed into sesquioxide. I replace then the water by

solution of gallic acid or of tannin and the image progressively appears

in ink-black. When I judge the image to be sufficiently intense I wash

the proof in rain water, in preference to ordinary water, which might

cause the gallic acid and tannin to turn brown. I sponge between sheets of

blotting paper and let the proof dry spontaneously."

"If in place of gallic acid I use a diluted solution of potassium

ferricyanide (red prussiate of potash), Prussian blue is formed in the

parts acted on by light. The preparation is even sensitive enough to

permit one to obtain an impression in the camera obscura in developing by

the ferricyanide."

"As to the proofs in gallate (or tannate) of iron, they can be transformed

into Prussian blue in a solution of potassium ferrocyanide (yellow

prussiate of potash) slightly acidified by sulphuric acid."

The paper most suitable for this process is that which has been previously

well sized with starch, as explained in a special paragraph of this

pamphlet. Paper prepared with a film of coagulated albumen gives also good

results. It may be prepared by brushing as well as by floating, but in

either case the paper should be wetted on the surface only and dried

rapidly at a temperature of about 115 deg. Fahr. (46 deg. C.) and kept in

a dry place. It does not keep for more than from ten to fifteen days,

owing to the hygroscopicity of the iron compound. Mr. Colas, who prepares

the paper for the Parisian market, I think, states that he avoids its

deterioration by keeping it wrapped in blotting paper, between two sheets

of India rubber, to exclude air and dampness. Silvered albumen and plain

paper, well desiccated, could be kept in that way for a certain period,

especially if the blotting paper is impregnated with sodium bicarbonate

and well dried.

Mr. A. Fisch advises to discard the preliminary washing and to develop

just on the removal of the proofs from the printing frame. In operating

in this manner the development is best made by floating, taking care that

the solution does not run off the back of the proof.

The developer may consist of a dilute solution of nutgalls or of

Tannin or gallic acid 4 parts

Oxalic acid 0.15 parts

Water 1,000 parts

After developing the proof should be washed rapidly--under a jet of water,

if possible--for were the iron salt and the reagent not soon removed, or

any remain in the paper, the ground would be tinted violet. And whatever

be the care taken, it very seldom occurs that the whites are pure when the

proof is dry. This for half-tone pictures has not a great importance, but

for the reproductions of plans it is sometimes objectionable. In fact it

must be acknowledged that none of the processes now at our disposal--if we

except the so-called Artigues process described further on--gives an

entirely satisfactory result. A simple and expeditious process, yielding

intense black impressions on a white ground, is yet to be found for the

reproduction of plans, maps, etc., without resorting to a negative cliche

or drawing.