Part 13 (1/2)

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 suns.h.i.+ne 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 was.h.i.+ng. 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 b.i.+.c.hloride 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 brus.h.i.+ng 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 b.i.+.c.hromate 1 to 2 grains Water 10 ounces

”Dissolve the silver nitrate in 1 ounce of water, the citrate and b.i.+.c.hromate 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 was.h.i.+ng 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: