Photographic Reproduction Processes

by Peter C. Duchochois

“The best process for fixing the photographs prepared with gold is as follows: As soon as the picture is satisfactorily [pg 15] brought out by the auriferous liquid, it is to be rinsed in spring water, which must be three times renewed, letting it remain in the third water five or ten minutes. It is then to be blotted off and dried, after which it is to be washed on both sides with a somewhat weak solution of hydriodate of potash. If there be any free chloride of gold present in the pores of the paper it will be discolored, the lights passing to a ruddy brown; but they speedily whiten again spontaneously, or at all events on throwing it (after lying a minute or two) into fresh water, in which, being again rinsed and dried, it is now perfectly fixed.”

As the chrysotype will be no more referred to, we shall state, first, that the image can be developed with a plain solution of silver nitrate or one acidified with citric or any other organic acid, which generally gives a brown impression that can be toned with an acid or alkaline gold bath, the color varying with the solution employed; and secondly, that the process may be employed to obtain outlines of any picture on paper or canvas to be colored in oil-paints. The impression developed with gold terchloride is pale blue, quite permanent, and does not at all interfere with the work of the artist. The canvas should first be washed with a mixture of alcohol and aqueous ammonia, then dried and rubbed with pumice stone powder to give a tooth. The modus operandi suggests itself.

The researches of Mr. C. J. Burnett on the application of uranium salts and other compounds to photography are recorded in the Photographic Notes of Ths. Sutton for 1857. We give in the following lines the most interesting parts of the two papers of Mr. Burnett:

* * * “The next class of processes are dependent on the sensitiveness to light of the salts of uranic oxide or sesquioxide of uranium, U2O3.”

“In the first process, the paper being charged with the uranic salt and exposed to the solar influence under the negative to be copied, is washed with a solution of the ferridcyanide or [pg 16] red prussiate of potash. The ‘Harvest Scene’ in the exhibition, being from an albumen negative lent me by Mr. Ross, the well-known Edinburgh photographer, is an example, the salt of the sesquioxide of uranium being in this case the hydrofluate, and the time of exposure from the strength of the albumen negative fully an hour of good sunshine. I have used for the solution of the uranic oxide for this process a variety of acids with very similar results; the sensitiveness of the prepared paper to light varying much, however. For instance, a collodion negative with the hydrofluate paper producing a very good print in half an hour of unsteady sun, while with a paper prepared with the tartaric acid solution of the oxide, it gave an equally good impression in less than five minutes of the same intermitting sunshine, indicating thus a difference of sensitiveness of six to one in favor of the tartrate.”

“The rationale of this process is the reduction of the sesqui-oxide of uranium, U2O3, on those parts of the paper exposed to the solar influence, to a lower state of oxidation, the photo-oxide UO, the salts of which have the property of forming with soluble alkaline ferridcyanides a rich chocolate-brown precipitate, while the salts of the sesquioxide are destitute of this reaction. Hence the brown deposit on the parts of the picture on which the sun has been allowed to act when the developing solution is applied, and the absence of any such appearance on those parts which have been protected from its influence.”

“As to the manipulatory details of this process, the paper is floated on the solution in a dark room and hung up to dry, and then preserved from light in a portfolio. If carefully secluded from light it appears to keep well. After exposure for the proper time under this negative, there is in some cases scarcely any visible impression; while in other cases, particularly when using the tartaric solution, I have found the impression very distinguishable, of a brownish or blackish shade, although still quite faint. The development is best conducted by floating it, anything like rubbing the picture being very objectionable.”

“When the picture has fully come out, which is generally from three to ten minutes at the very most, it is removed from the [pg 17] developing bath, placed in cold water and washed very gently for a few minutes, the water being frequently changed till it ceases to acquire a yellow tinge from the dissolved red prussiate. The picture is then drained from the water, pressed between folds of blotting paper, dried (I dry in the dark), and the process is complete. * * * I may state, as one recommendation of this process to ladies and other lovers of clean hands, that any brown stains left by it on the fingers or elsewhere are at once removable by a little weak ammonia or soap and water. * * * I would particularly suggest, as deserving of notice, the development of the salts of sesquioxide of uranium, and still more iron, by the metals and metallic-cyanic alkaline salts, as also by the mellonides and nitro-prussides, and the latter also by itself and as developed by many metallic salts.”

“I have since had the opportunity of trying the nitro-prusside of sodium, which, by itself, gives a blue and white picture, in color like that obtained from the red prussiate of potash.”

“When mixed with a solution of ammonio-nitrate of copper, previous to its application to the paper, the color obtained is pale purplish pink or peach-blossom color. By mixing it in the same way with ammonio-oxalate of sesquioxide of iron, we get a dull green picture, changeable through intermediate stages into brown by alkaline carbonates, and that into a dirty black by gallic acid. It may be well to know that the blue of the picture given by the red prussiate in the process of Sir John Herschel may be considerably modified or entirely changed to another color, in many ways, without interfering with the purity of the white ground, by steeping the picture, after the undecomposed red prussiate has been washed out, in solution of salts of various metals, copper, uranium or cobalt, for instance, and that the colors so produced may be modified as desired, according to the stage at which the action is stopped.”