Page:Popular Science Monthly Volume 22.djvu/417

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Another very decided advance in photography is the doing away with glass as a support for the emulsion. Mr. Warnerke has perfected a process by which the photograph is taken on paper instead of on glass. He has a sensitive tissue which can be made of any length, and can be rolled on a roller and exposed in the dark slide. By turning another roller, a fresh surface is brought into the plane of the focusing-screen. The sensitive tissue is developed in the ordinary way with alkaline development. The film can be either stripped off, or else transferred to glass. In the latter case, we come to another point which marks a distinct advance. Mr. Warnerke has found that when you develop a gelatine plate with alkaline development, the parts which have been acted upon by light, and which have been developed, become insoluble in hot water. He is thus able, after development, instead of using the hyposulphite bath to fix the print, to transfer it to glass, and wash away with hot water the parts of the film which have not been acted upon by the light; and he thus gets a transparency. To do this, it is necessary that the back surface of the gelatine film should be exposed to the water, as in carbon printing, and this is secured by transfer to glass. Mr. Warnerke is not satisfied with doing away with glass for the camera, but he does away with glass for printing; and, in order to accomplish this, he retransfers the negative from the glass to a sheet of gelatine. I may say that the glass is freshly collodionized, and this enables the film to strip off readily. It is one of the advantages of these negatives that you can print from either side, each one yielding sharp points—a desideratum when using processes where reversed negatives are required. In the matter of gelatine films, we have Professor Stebbings's, which are really workable. The gelatine emulsion is apparently flowed on an insoluble film on glass, which is then stripped.

The next point I touch upon is the enlargement of negatives. The best way I know of, of getting an enlargement of a negative, is one that was brought forward a few years ago by Mr. Valentine Blanchard. He takes the original negative which he wishes to enlarge, and places it in an enlarging camera. He then takes a transparency of the exact size he wants his negative to be. He next takes a piece of common albumenized paper, and prints that transparency upon it, and by this means gets a very soft and beautiful negative. If you have a hard negative, it is almost impossible to get a soft transparency by the wetplate process; but, by this artifice of "printing out" your transparency and using that as a negative, you get a decidedly soft paper negative.

One of the new applications of the gelatine process is the development of a print on paper coated with gelatino-bromide. The paper is prepared by coating ordinary paper with gelatino-bromide (of the most sensitive kind, if you like). Such paper can then be exposed to the image formed by an ordinary magic-lantern; by that means you