Photographic Reproduction Processes Part 6

The process published in 1865 by Wothly is as follows: A sheet of paper is sized by brus.h.i.+ng with a paste made of 24 parts of arrowroot in 500 parts of water, to which are added a few drops of a solution of citric or tartaric acid, then coated with a collodion consisting of 100 cubic centimeters of plain collodion, a few drops of oil of turpentine and 30 cubic centimeters of the following sensitizing solution:

Nitrate of uranium 30 to 90 parts Chloride of platinum 2 parts Alcohol 180 parts

The time of exposure is about that required for paper prepared with silver chloride. The image is bluish-black but weak. After was.h.i.+ng the print is immersed in a solution containing 0.5 parts of chloride of gold for 2,000 parts of distilled water, and then fixed in a bath of sulphocyanate of pota.s.sium, which tones the image blue-black.

It may happen that the proof is slightly tinted red. This arises from a small quant.i.ty of lime in the paper which forms uranate of calcium.

To prevent the proofs turning yellow, it should be washed in an exceedingly weak solution of acetic acid.

If, after exposure, the print is immersed, without it being washed, in the gold bath, the image becomes rose-red, but the whites remain pure. The effect is peculiar.

H. COOPER'S PROCESS (1865).

PREPARATION OF THE PAPER St. Vincent arrowroot 200 grains Boiling water 10 ounces

Crush the arrowroot to fine powder, then rub it to a paste with a little water, and let an a.s.sistant pour a few drams of boiling water while you keep stirring all the time; finally, let him add the rest of the boiling water, the operator still continuing the stirring. The paste is allowed to cool, and will be thicker when cold than when hot. Remove the upper portion entirely when quite cold, otherwise, if any left, it will give rise to streaks. The author insists upon the necessity of all these cares. Two sheets of paper are now placed side by side on a flat board, then the surface of the first is covered with the paste by means of a sponge, proceeding, before you leave it, all over the sheet in a horizontal direction; the second sheet is covered in a like manner. By the time the second sheet is pasted, the first one will be partially dry.

The sponge is now drawn over each sheet, in succession, in a perpendicular direction in order to efface the streaks from the first sponging. If the paste drags in a slimy manner, it is too strong, and a fresh arrowroot must be prepared, because dilution only ends in failure. Why dry, the paper is rolled under moderate pressure, and when it lies smoothly the maximum pressure may be applied.

PLAIN COLLODION.

Alcohol 12 ounces Ether 4 ounces Pyroxyline 80 grains

SENSITIVE COLLODION.

Plain collodion 1 ounce Nitrate of uranium, pure 30 grains Nitrate or silver 5 grains

Add the uranium first, and as soon as it has dissolved all that it can, add a grain or two of soda, and when settled pour off the supernatant collodion and add the silver.(14) To coat the paper with collodion, use a board with a handle beneath, such as is used by plasterers. On this place a sheet of paper, the edges being turned up about the sixteenth of an inch; this enables the whole of the sheet to be covered without spilling the collodion or allowing it to run on the back of the paper.

There is a marked difference in the appearance of the prints when they leave the pressure frame. Some samples of collodion cause the picture to print of a beautiful green, others of a rich brown, and some of a yellow or orange tint. The last take the longest of all to tone, and difficultly a.s.sume the tint of well toned silver prints,(15) those printing to green or brown tone very rapidly.

After printing the pictures are placed in diluted sulphuric acid, 1 to 30 of water, until the high lights are perfectly clear and white; this takes from ten to fifteen minutes. After was.h.i.+ng well under a stream of water, they are placed in the toning and fixing bath.

TONING AND FIXING BATH.

Sulphocyanide of ammonium 1 ounce Water 12 ounces Chloride of gold 1 to 3 grains

After removing from this bath, the prints are immersed for a few moments in water, and then rapidly washed.

FORMULA FOR PREPARING THE PYROXYLINE Nitric acid, sp. gr. 1.30 12 fluid ounces Sulphuric acid, sp. gr. 36 fluid ounces 1.845 Water 8 fluid ounces Temperature 130 degrees Fahr.

Time of immersion 15 minutes.

X'S PROCESS (1865). (Secrets of the Uranotype)

_Preparation of the Uranium Compound.-_Precipitate the nitrate of uranium from its solution by concentrated liquid ammonia. Let settle the precipitate, decant, and wash in several changes of water. Dissolve it by heat in pure nitric acid, _taking care not to add an excess of acid._ The ammonio-nitrate of uranium salt is then crystallized and dried. Mix a solution of 6 drams of this salt, dissolved in 3 drams of water, to a solution of 15 grains of silver in 30 minims of water, and crystallize.

This salt is called _ammonio-nitrate of uranium and silver._

SENSITIZING SOLUTION.

Ammonio nitrate salt 3 drams Alcohol 8 drams Distilled water 15 drops Nitric acid, pure 1 drop

_Plain Collodion.-_Dissolve in a small quant.i.ty of ether 1 dram of Canada balsam and 1 dram of castor oil, filter and let evaporate the solution to the consistency of oil.

Of this, add 10 minims to a collodion made of

Alcohol 10 ounces Ether 20 ounces Pyroxyline 220 grains

SENSITIVE COLLODION Plain collodion 12 drams Sensitizing solution 6 drams Nitric acid 2 or more drops

Keep this collodion in the dark, as it is quite sensitive.

PREPARATION OF THE PAPER Arrowroot, pulverized 1 ounce Water 32 ounces Solution of acetate of 10 drops lead

Heat to 100 deg. Fahr. and then add four ounces of alb.u.men. The paper is floated on this solution for five minutes and hung up to dry. The sizing may also be applied with a sponge in the manner often described.

The proofs should be slightly over-printed and, before toning and fixing, placed for about ten minutes in the following solution:

Distilled water 40 ounces Acetic acid 1 ounce Hydrochloric acid 1 ounce

After was.h.i.+ng in several changes of water, the proofs may be toned in any toning bath, and then fixed with sulphocyanide of pota.s.sium, was.h.i.+ng afterwards in the usual manner.

THE PLATINOTYPE.

This process, discovered by William Willis,(16) yields very fine impressions which wholly consists of platinum and are, therefore, chemically permanent. It has been described theoretically and practically by Pizzigh.e.l.li and Kubl in a paper for which the Vienna Photographic Society has awarded the Voightlander prize.(17) The following is an abridgment of this important process, as described by the authors:

The paper, calendered or not,(18) is sized with gelatine or arrowroot.

The color of the proof with the latter size is brownish black, and bluish black with the former.

To prepare the gelatine solution 10 parts of gelatine are soaked in 800 parts of water and then dissolved at a temperature of 60 deg. C. (140 deg.

Fahr.), when 200 parts of alcohol and 3 parts of alum are added and the solution filtered.

To prepare the arrowroot solution 10 parts of the substance are powdered in a mortar with a little water and mixed to 800 parts of boiling water, added gradually in stirring. After boiling for a few minutes 200 parts of alcohol are added and the mixture filtered.

These solutions are employed warm. The paper is immersed for two or three minutes and hung up to dry in a heated room, then immersed a second time and dried by hanging it up in the opposite direction, in order to obtain an even coating.

The pota.s.sic platinic chloride is an article of commerce. It should be soluble without residue in 6 parts of water and without acid reaction. In this proportion it const.i.tutes the normal stock solution employed in the various formulas.

The standard ferric oxalate solution is also found in commerce. Treated by pota.s.sium ferricyanate it should not be colored blue, nor become turpid when diluted with one-tenth part of water and boiled. The former reaction indicates that it contains no ferrous salt, and the latter no basic oxalate.