Dr Jb Obernetter's Process 1863

Copper chloride 100 parts

Ferric chloride, sol. sp. 13 parts

gr. 1.5

Hydrochloric acid, conc. 12 parts

C. P.

Water 1,000 parts

Float the paper on this solution for about two minutes and hang it up to

dry. The keeping quality of the prepared paper is remarkable; it has been

kept for two years without apparent change; its sensitiveness is at

one-third greater than that of silver albumen paper. Unless developed

within an hour or two, the vigor of the proof is much impaired; after

twenty-four hours a print can be taken over on the same.

When exposed, only a faint image is visible. It should be fixed in the

following solution:

Potassium sulphocyanate 12 parts

Sulphuric acid, conc. 1 part

Sensitizing solution 10 to 12 parts

Water 1,000 parts

A print is floated on this solution, face downward, for three or four

minutes, taking care to agitate the liquid as little as possible; the

print is afterwards immersed and another one floated in its place, thus

proceeding until all the prints are immersed or the solution can hold no

more. A fresh solution is then added to strengthen it: the older the

solution the more rapidly and better it works. In this developer copper

cyanide is precipitated on the parts acted on by light, and this exactly

in the proportion to the luminous action. The time of immersion depends

on the method selected to finish the proofs; it its from five minutes to

half an hour. If the proof is immersed for, say, twenty-four hours, the

image comes out in a relief which may bring the shadows to two lines in

depth. When well developed and thoroughly washed, the proof can be dried

and the subsequent operations made at any convenient time.

Various processes may be employed to give to these proofs the tone

required; thus: the prints well washed are placed in a solution of

ferricyanate of potassium at 6 to 12 per 100 of water, where they take a

red color increasing in intensity. If left over night the color becomes a

splendid velvet deep red with perfect clear whites. To obtain the color

of silver photographs one hour's immersion is sufficient. After this

operation the proofs are washed until the water is no more tinged yellow.

By immersion in

Ferrous sulphate 100 parts

Iron sesquichloride 40 parts

Hydrochloric acid 80 parts

Water 200 to 300 parts

the proofs undergo the following gradation of colors: red, reddish violet,

blue-violet, black and greenish black. As soon as the desired color is

obtained, the proofs are washed in acidified water and dried.

The most beautiful purple violet is obtained by leaving the proofs in the

iron solution until green-black, and then washing for a moment in a dilute

solution of sub-acetate of lead.

A brown-black may be produced by treatment, after washing, with an

ammoniacal solution of hypermanganate of potash.

A weak solution of nitrate of silver also yields very fine pictures, but

the exposure should be very short, and the proofs must be fixed in water

containing a small quantity of oxalate of ammonia.

In order to impart to the proofs the gloss of silver photographs, they

should be albumenized in the ordinary manner, and the albumen

insolubilized by well known means.

The chemical actions in this process I explain in the following manner: On

the paper there are Fe2Cl3 and CuCl, the latter in excess. By the action

of light, and according to the transparency of the negative, Fe2Cl3 is

reduced to FeCl, while CuCl suffers no alteration.

If the paper be immediately placed in an absolutely dry room after

exposure, the picture remains unchanged. In a moist atmosphere FeCl

attracts moisture and, with a part of CuCl, is so decomposed that Fe2Cl3

is formed together with Cu2Cl.

After this action has commenced, if the proof be not immediately immersed

in a solution of sulphocyanate of potassium, Cu2Cl passes over to a higher

combination of chlorine, and the paper is again fit to be impressed anew

by the action of light.

As long as FeCl or even Cu2Cl is present, if the print is immersed in the

sulphocyanate solution, sulphocyanate of copper is immediately formed on

the reduced parts, while on the others the sulphocyanide of copper, formed

and dissolved by the sulphocyanide of potassium in excess, becomes decom-

posed with water in soluble sulphocyanide of copper and deposited as such

on the parts already covered with the salt.

Frequently the prints appear yellow from formation of the double

sulphocyanide of copper, but the color disappears by washing in water.

Red coloration is due to decomposition into ferrocyanide of copper.