C.J. BURNETT'S PROCESS(1857).

“A capital process for many purposes,” says Mr. Burnett, “is to float or steep the paper in a mixed solution of bichro­mate of potash and sulphate of copper, as for Hunt's chromo­type process.36 I have mixed gelatine, or occasionally grape sugar, or both with the solution;37 but instead of developing it with nitrate of silver, as in chromotype, wash out the salt unaltered by light, and develop by floating on a solution of ferrocyanate of potassium. The purple red color of the copper salt which now forms the picture may be modified or changed [pg 110] in many ways,38 viz., by soaking the picture, after the ferrocyanate of potassium has been washed out of the lights, in a solution of sulphate of iron. Solutions of gallic acid, tannic acid with alkalies of carbonate, may also be employed to modify or change the color. This process has the advantage that one may regulate the exact tone (black or useful neutral tint) to the greatest nicety by the time we allow the print to remain in the iron toning bath.”

GODEFROY'S PROCESS (1858).

Float the paper upon the following solution for three minutes and hang it up to dry:

DE LA BLANCHERE'S PROCESS (1858).

Filter the solution and keep it in the dark.

The paper should be sized with a gelatine solution at 5 per 100 of water, and, when dry, kept in the dark.40 It is sensi­tized by floating five minutes.

The exposure under a negative varies from fifteen to twenty minutes in the shade, and from one to three minutes, at the most, in sunshine. As a rule, it is advisable to somewhat under­expose in order that the development be regular, progressive, under control.

The image is developed by floating, or immersion in

When the image is intense enough it is washed in several changes of water, then toned in a solution of gold at 1 per 1,000 of water acidified with traces of hydrochloride acid.41

The following bath develops slowly, and gives very rich purple tones without toning:

The developing solutions should be as little acid as possible, but not neutral, for then the proofs would be veiled and grayish.

The image can also be developed in a solution of gold, or in a very weak solution of mercuric chloride at 1 per 10,000. The proof must be extremely well printed and left for from [pg 112] two to five minutes in the mercuric solution. If the time of exposure is right, the image will change but little in the solu­tion, and will take, when treated with silver nitrate, the most splendid tones.

The proofs should be carefully washed when finished. If they were developed with silver, they must be immersed in diluted aqueous ammonia, which will perfectly clear the whites. If developed with chloride of gold, the water should be heated to 60 to 80 deg. C. (140 to 176 deg. Fahr.)

HOUDOY'S PROCESS (1858.)

The paper is floated upon a lukewarm solution of gelatine at 5:100, and when dry, on a bath of uranium at 10 or 15 per 100 of water. After exposure to the sun the image is developed with a solution of silver nitrate acidified with acetic acid. The exposure varies, according to the nature of the negative, from one to ten minutes; it must be long enough for the image being developed in from thirty to forty seconds. It is then removed from the silver bath and placed in the following:

In this bath the image takes a great vigor and appears entirely on the surface of the paper. When the proof has been too long exposed it should be washed slightly before placing it in the iron bath. Developed, the image is, gener­ally, of a sepia tone, which can be turned to black by a solu­tion of chloride of gold, 1:1,000, washing afterwards as usual.

NIÈPCE DE ST. VICTOR'S PROCESS (1859).

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 [pg 114] 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 potassium 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.

“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:

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 [pg 116] neutral or does not evolve the smell of ammonia. The precipitate is then placed in an evaporating dish, and by small quantity 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:

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 constitutes 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 cir­cumstances tannin (gallo-tannin) produces a blue-black image; catechu-tannin43 and quino-tannin give green, etc. Employed as [pg 117] a developer, potassium 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).

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 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:

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 [pg 118] 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

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 [pg 119] 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 decom­posed 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.

L. LIESEGANG'S PROCESS (1865).

Pour ammonia into a nitrate of uranium solution, wash the precipitate of uranate of ammonia in distilled water, then dis­solve in citric acid.

Mix this solution of citrate of uranium and a little of a solution of chloride of gold with a paste prepared by dissolv­ing tapioca in hot water. The quantity of chloride of gold must be small and the heat not too great, otherwise the gold would be reduced.

Spread the mixture with a sponge on the paper, which takes a brilliant yellow color, and expose when quite dry; the proofs have the delicacy and vigor of albumen prints.

The proofs come from the frame with a bluish-black color; they should not be toned, but merely fixed by washing until the yellow color of the paper has disappeared.

The color of the picture can be changed to a purple by a solution of chloride of tin.

GUARBASSI'S PROCESS (1867).

The paper is floated in the dark for four or five minutes on a saturated solution of bichromate of potash. When dry, it is printed a little longer than for silver prints and afterwards floated, face upwards, on a water bath until all the unaltered bichromate is dissolved. It is then immersed in the following solution, which improve by use and tones the pictures to a reddish color:

This solution should be prepared, filtered and allowed to stand for some time before use. The print is left in the bath until it has assumed an intense red color, the whites remain­ing perfectly pure. It is then washed and put in another bath to obtain a brownish tint. This bath is thus composed:

The print must be immersed at once, and when, in a short time, it has assumed the proper color, it should be washed immediately.

The picture is toned in a very diluted solution of chloride of gold, 1:7,000, in which the color passes from a light brown to a deep black or a violet black tone, when it is washed in two changes of water.

A. POITEVIN'S PROCESS (1870).

“I use a paper prepared with iron sesquioxide rendered sensitive to light by tartaric or, better, citric acid in concen­trated solution. This paper, after desiccation and exposure to light, possesses the property of reducing the solution of silver nitrate and that of chloride of gold, and of turning blue with a solution of potassium ferncyanate in the parts where light [pg 121] has reduced the iron sesquichloride into the oxide at the minimum.”

“To coat the paper with an equal layer of iron sesqnioxide, I brush it with a tuft of fine linen dipped in a solution of iron perchloride at 10 or 12 per cent. of water, and dry the sheets in the dark. I immerse afterwards these sheets, one after the other, in a tray containing aqueous ammonia, in such a man­ner as to well wet each sheet successively. A sufficient num­ber of sheets being immersed, I pour off the ammonia in a vial, and, in the tray, I wash them several times, and remove them one by one to hang them up to dry, even in full light, the iron sesquioxide not being sensitive to light.”

“The paper can be prepared in quantities beforehand. To use it I apply upon each sheet a solution of citric acid at 30 or 35 per cent. of water44—which may be done by daylight—and let them dry in the dark.”

“Exposed under a negative of the ordinary intensity, the paper is impressed in sunshine in a few minutes; in the shade it requires about the same time as chloride of silver paper.”

“After exposure the image is not visible, and without being obliged to shelter it from light, I immerse the print in a solution containing about 1 per cent. of silver nitrate. This solution can be used over and over again, by adding to it a little of the silver salt. It does not become turpid by use; it simply turns slightly green from formation of iron nitrate. The image appears soon and rapidly becomes vigorous; in half an hour it will be completely developed. When the exposure is sufficient the color is deep sepia, but not so intense if the quantity of citric acid is feeble. No fixing is necessary; it suffices to wash in several changes of waters.”

“The image can be toned with great facility by a weak solution of gold or of platinum chloride, or, better, by a mix­ture of these two salts. If the impressed paper be treated by a very diluted solution of potassium ferrocyanate, one obtains very pretty blue proofs.”

“A weak solution of gold chloride develops a violet image. A solution of platinum chloride has no effect.”

“All the various phases of this printing method can be followed in full (diffused) light; there is only the desiccation of the paper when sensitized with citric acid, which requires to be done in the dark.”