Popular Science Monthly/Volume 13/August 1878/A New Photographic Process
|A NEW PHOTOGRAPHIC PROCESS.|||
SO manifold are now the uses of photography that we need not dwell upon the importance of processes which allow of the employment of easily-handled apparatus, and which do away with cumbersome and fragile glass plates. Deyrolle's photographic process, described below, answers all the requirements of portability.
The idea of substituting sensitive paper for heavy, brittle plates of glass is not new, but all the processes hitherto offered labor under the serious disadvantage of necessitating a long exposure. Besides, the proofs are usually imperfect on account of the granulations which the paper leaves on the positive. M. Deyrolle's collodionized paper does not present these difficulties. It is covered with a special coating, insoluble in ether, alcohol, or water, and thus it undergoes all the operations of photography without change. This paper is collodionized and treated precisely as though it were glass. It is, in fact, quite equal to glass plate for the uses of photography, and in addition possesses the following advantages:
The layer of collodion is so firmly attached to the coating of the paper that it cannot be injured by contact with a hard object, nor even by slight friction. Besides, the picture can be developed by total immersion in the developing liquid, instead of pouring the latter on the collodion layer, as in the case of plates of glass, an operation that requires some dexterity and long practice.
This paper will retain all its sensibility for about two years, provided it be sheltered from light and moisture; it is not affected either by cold or heat. Hence it is destined to be of great use to travelers who explore remote regions.
After the light-impression has been made on the paper, it remains to develop the image. This operation presents no difficulty, success depending, so to say, only on the time of exposure. First, the paper is dipped in common water, care being taken to make the immersion complete. There it must remain for at least five minutes, or until the paper, which was beginning to curl, becomes perfectly flat. In the mean time the following solution is prepared in quantity only sufficient for the pictures to be developed at once, for oftentimes it decomposes in the course of a day or two:
|Glacial acetic acid||20||grammes.|
Into a basin with flat bottom, and of a size corresponding to that of the proof treated, is poured enough of the above solution to completely submerge the proof; a depth of three or four millimetres is amply sufficient. Into this is dipped the proof after taking it from the water and draining it, the collodionized side uppermost. After inclining the basin in every direction, so as to cause the liquid to pass several times over the proof, a portion of it is poured into a glass, and then we add to it a few drops of the following solution:
|Crystallized nitrate of silver||5||"|
Stir well, so as to mix thoroughly. The whole is poured into the basin, which again is inclined as before. The image now appears; seven or eight minutes suffice to completely develop it, with the sky or the lighted parts of an intense black.
When the proof is sufficiently developed it is put in water, and then dipped in a solution of hvposulphate of soda, 40 per cent., to fix it; it is then freely washed in water in the usual way. It is now dried between leaves of silk-paper or blotting-paper.
Treated in this way the proof is perfectly secure: it is not affected by changes of temperature, and may be exposed either to damp or to drought without the least injury. To preserve it, we have only to place it in a book or in a portfolio, so that it may not be creased or rubbed on the collodionized side.
When we would take positive proofs, we detach from the paper the layer of collodion, thus getting the image on a thin transparent pellicle.
This is a very simple operation, consisting merely in adding to the collodion layer firm and transparent substances, till the cliché attains the proper consistence. To this end, we prepare a normal collodion of the following composition:
|Alcohol of 40°||2||"|
Lay the proof on a plate of glass, having first turned up the edges all round, so that the liquids to be poured upon it shall not overflow. On the collodion layer containing the image pour the normal collodion, beginning at one of the corners of the proof most remote from the operator. Then incline it slightly, so as to cause the liquid to flow; and, after the entire surface has been covered, the excess of liquid, if any there be, is poured back into the bottle. Then the cliché is laid flat in a roomy box, or in any other place where it will be sheltered from dust,
and left for a few hours to dry. When fully dried, or when it is no longer sticky to the touch, we again, in the same way as before, pour over the layer of normal collodion a layer of caoutchouc dissolved in benzine. When this has become dry, we apply a second layer of normal collodion, then caoutchouc again, and, lastly, a final layer of normal collodion.
The cliché is now left to dry for twenty-four hours, and it is trimmed all around. Then, at one corner, the paper is separated by a finger-nail from the coating formed upon it. Having in this way loosened the coating at one corner, it may easily be stripped off altogether, with a little care, leaving the paper clean and white, as though it had never undergone any treatment. In this way is got a negative at least as transparent as though it were on glass; but it possesses the advantages of not being brittle, of not being damaged by rubbing, of occupying but little space, and, finally, of giving better proofs than can be got from clichés on glass.
To utilize this process, M. Deyrolle has constructed a strong but portable apparatus, made almost entirely of copper and iron, weighing not over 400 grammes for one producing proofs 0.13 metre by 0.18 metre, or 700 grammes for one producing proofs 0.24 metre by 0.18 metre (see figure on page 443).
The camera, which, when folded, is only four centimetres high, is held distended by two steel rods, which connect the frame of the object-glass with that for the slide. The support for the apparatus consists of three double legs with joints; these are fastened by thumb-screws to a triangular table. The stem supporting the camera is articulated with the centre of this table by means of a ball-and-socket joint, which allows the instrument to be turned in any required direction. The ball may be made fast at will by means of a steel spring. This new form of foot has the great advantage of being extremely light, and of allowing the camera to rest in any plane whatever.
We would add that, when this system is employed, the complete outfit of an explorer who wishes to take 300 negatives will not weigh over six kilogrammes, including the instrument, the clichés, and all the chemicals needed for developing the negatives.
- Translated from La Nature by J. Fitzgerald, A.M.