Photographic Reproduction Processes Part 13

Red Prints.

Float the paper for fifteen or twenty seconds on a 20 per cent. solution of nitrate of uranium and dry before the fire in the dark room. This paper can be prepared many days before use. Expose in sunshine from eight to ten minutes, according to the intensity of the light and the quality of the negative, then wash in moderately warm water (50 to 60 deg. C.) for a few seconds. This done, immerse in a solution of red prussiate of potash at 2 per cent. of water; in a few moments the proof will become of a fine blood-red color, like "sanguine." Wash, etc.

Green Prints.

Make a red print as above described, immerse it for a few minutes in a solution of nitrate of cobalt and dry it without washing. Fix then in a solution of sulphate of iron at 20 per cent. of water and 4 of sulphuric acid. Wash and dry before the fire.

Violet Prints.

Prepare the paper in the uranium bath, expose, wash and develop in a solution of chloride of gold, 1:200, until the proof has a.s.sumed a fine violet color. Wash in several changes of water.

Blue Prints.

Sensitize the paper with a red prussiate of potash solution at 20 per 100.

Let dry, expose until the proof is slightly blue; immerse it for five or ten seconds in a saturated solution of bichloride of mercury, wash only once and immerse in a solution of oxalic acid-saturated when cold-heated to about 55 deg. C. Wash in three or four waters and let dry spontaneously.

Black Prints.

Float the paper on a mixture by equal volumes of a solution of iron perchloride and another of uranium nitrate, each at 10 per 100 of water.

Expose and develop on a saturated solution of gallic acid.

DR. T.L. PHIPSON'S PROCESS (1861).

Take a solution of perchloride of iron and, having precipitated the peroxide with ammonia, collect the precipitate on a filter and wash it with boiling water. Add the precipitate in excess to a warm solution of oxalic acid. A beautiful emerald green solution is obtained, which must be a little concentrated by evaporation and then set aside in a dark room for use. The paper is floated for ten (?) minutes upon the green solution of ferric oxalate, to which has been added a little oxalate of ammonia and hung up to dry in the dark.

Expose under a negative for from ten to twenty minutes, according to the weather, and wash well the paper with rain water. Spring water will not do on account of the lime it may contain, which will form oxalate of lime in the paper (insoluble). When all the non-decomposed oxalate is washed from the proof, a feeble image of oxalate of protoxide of iron, scarcely visible, is left on the paper. To develop it and to obtain the vigor, the tone and color of silver prints proceed as follows:

Plunge the proof for a little while in a (weak) solution of permanganate of pota.s.sium to which a few drops of ammonia have been added; in the bath the image becomes brown and distinctly visible. It is then withdrawn and immersed in a solution of pyrogallic acid for half an hour, after which it is washed and dried.

The image thus obtained can hardly be distinguished from silver prints; the tone is soft, brilliant and permanent.

This process is quite original and interesting. The theory is as follows: Under the action of light the ferric oxalate is reduced in the ferrous salt, insoluble, which, after the print has been cleared from the ferric oxalate, is oxidized and reduced into ferric oxide by the alkalized permanganate, the latter then forming colored compounds with reagents.

It has been lately published in England under the name of "kallitype," a new process-or old, ad libitum-which consists in developing the image in ferrous oxalate by a peculiar silver compound whose formula is given below. The paper is prepared by brushing with a strong solution of neutral ferric oxalate dried rapidly-which is a sine qua non when using deliquescent salts; and after exposure the image is developed, etc.

Silver nitrate 50 grains Sodium citrate 800 grains Pota.s.sium bichromate 1 to 2 grains Water 10 ounces

"Dissolve the silver nitrate in 1 ounce of water, the citrate and bichromate in the remainder and mix. The precipitate-silver citrate and chromate-is then dissolved by adding 1 dram of ammonia .880, and after 35 drops of strong nitric acid has been added the solution is ready for use."

This process reminds us that of Robert Hunt (1842), and that of more recent date (1863), of Borlinetto, who developed the image in black with a silver nitrate alcoholic solution, 1:500, and after washing the picture in a solution of citric acid, 1:10, fixed it by aqueous ammonia. But, although that is not absolutely necessary, we would advise one working this, or similar processes in which a silver salt is employed for developing, to fix the image, after treatment with citric acid to clear the proofs from iron salts, in a solution of ammonium sulphocyanate-which has not the injurious effect of sodium thiosulphate (hyposulphite)-in order to prevent the paper to be tinged by the reduction of the silver nitrate which is mechanically retained in its fiber.

The solution of ammonium sulphocyanate should be compounded with auric chloride to tone the picture at the same time it is fixed; thus:

Ammonium sulphocyanate 35 parts Gold terchloride 0.15 part Water 350 parts

The solution can be used over again.

In the processes devised by Dr. Phipson, Monckhoven and other authorities, the double ammonio-ferric oxalate is rightly recommended instead of the simple oxalate. Not only is the preparation more sensitive to the luminous action, but better half tones are obtained. As usual, it is advantageous to size the paper with starch.

The ammonio-ferric oxalate is prepared by precipitating ferric chloride or sulphate by aqueous ammonia, then washing the precipitate collected on a filter until the washing water be neutral or does not evolve the smell of ammonia. The precipitate is then placed in an evaporating dish, and by small quant.i.ty is added a hot solution of ammonium oxalate until it is nearly (not entirely) dissolved, when the solution is set aside for a few hours, then filtered and evaporated to crystallization. For use, the crystals of ammonio-ferric oxalate are dissolved in the proportion of 1 for 5 of distilled water. The solution as well as the crystals should be kept in the dark.

If one object to the trouble of crystallizing, the solution can be prepared by dissolving the ferric oxide in a hot solution of 30 parts of ammonium oxalate and 25 parts of oxalic acid in 180 parts of water observing that the oxide must be in excess.(42)

The following sensitizing solution gives also excellent results:

Ammonio-ferric oxalate 10 parts Ammonio-ferric lactate 4 parts Water 100 parts

After exposure, which varies from five to ten minutes, according to the intensity of the light and the printing quality of the negatives, the picture appears negative from formation of ferrous oxalate. It may be developed in a great many ways: by a solution of silver nitrate at 2 or 3 per cent. of water acidified slightly by an organic acid-citric acid, for example-or a diluted solution of ammonio-nitrate of silver, which most likely const.i.tutes the best developer; the image is black and consists of metallic silver and ferric oxide, with formation of silver oxalate, which dissolve in the ammonia. If the print be treated by a weak solution of aqueous ammonia, the image turns green, then brown, and if, before the latter coloration is obtained, gallic acid or pyrogallol be added, the image becomes bluish-black or brown-black. In the same circ.u.mstances tannin (gallo-tannin) produces a blue-black image; catechu-tannin(43) and quino-tannin give green, etc. Employed as a developer, pota.s.sium ferricyanate develops an image in prussian blue, and auric chloride one in the characteristic violet metallic gold. To fix the images obtained by the latter reactions, it suffices to wash them in a few changes of water, and, if developed with silver, they can be toned by any of the alkaline solutions of auric chloride used in the printing out silver process, etc.

The photographs obtained by all these processes are permanent.

DR. J.B. 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 least one-third greater than that of silver alb.u.men 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:

Pota.s.sium 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 pota.s.sium 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.