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The photographic news
- Bandzählung
- 12.1868
- Erscheinungsdatum
- 1868
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 503, April 24, 1868
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Zeitschrift
The photographic news
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Band
Band 12.1868
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- Titelblatt Titelblatt I
- Kapitel Preface III
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- Register The Index To Volume XII 619
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Band 12.1868
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April 24, 1868.] THE PHOTOGRAPHIC NEWS. 201 of the materials employed, and the complicated form of several of the operations. How long these objections will remain in the way time alone will show. The process possesses, however, several important advantages, the greatest of them being the extraordinary sensitiveness of the carbon paper. In summer, during favourable weather, this quality is not so apparent and striking as in the foggy November weather. On a dull November day, when a silver print is scarcely sufficiently printed if exposed from morning till evening, I have been able to obtain an over-exposed carbon print from a negative of average thickness in sixteen minutes and a half, and in nine minutes and a half a remarkably vigorous carbon print from one of Loescher and Petsch’s portrait negatives ; and this with carbon paper which was by no means of the most sensitive description, but which, under thick negatives, required to be exposed up to 18° of the photometer scale, and with thin plates up to 14° ; with paper prepared by myself, I need not expose further than 15° for a thick, and 11° for a thin negative. This sensitiveness of the carbon paper is a matter of con siderable importance in commercial photography, especially when work is carried on on a large scale. If, for instance, the production of a thousand copies were required from one carte-de-visite negative by means of the silver process, the time required for printing the same would be about fifty-six days, or nearly two months; with the carbon process, which is at least eight times as sensitive as the silver method, the thousand pictures might be turned out in the space of seven days. In the course of last month I made a series of observations with reference to the best method of effecting the transfer of photographs upon glass, suitable not only for the carbon process, but for other methods, such as photo enamelling, &c. One of the principal points to be attended to, mentioned by Wilson in his article on carbon printing, is to prevent the formation of air-bubbles in the paper during the opera tion of developing. Freedom from these imperfections may be secured by the very simple precaution of allowing the carbon print fastened to the india-rubber paper to remain for a short time in cold water previous to development. The formation of bubbles results from the presence of air in the pores of the india-rubber paper; if the latter is immersed suddenly in warm water, the air expands quickly, and swells into bubbles under the film of india-rubber; but if the papers are first placed in cold water for a short time (the india-rubber paper uppermost), the air is gradually expelled by the water in minute globules. After remaining thus for a quarter of an hour, the paper may be transferred to a warm water bath, where the picture is detached and developed. The prior immersion in cold water possesses another advantage : it removes the chromate from the paper, which thus becomes insensitive to light, and allows the de velopment of the picture to take place in the daylight, by which means this important operation may be more success fully controlled. The developing process I have already described in a former communication. After the picture has been fully de veloped the paper is rubbed over with a brush, to remove any superfluous carbon particles; and it is then dried, and coated with gelatine. During the last-mentioned operation the formation of minute bubbles often occurs, especially at a cool temperature; but these are easily removed by the application of the finger. Wilson recommends the transfer of the picture to Stein bach paper, but this operation docs not finish the process, as the print must afterwards be mounted upon cardboard. In stead of this, therefore, the picture (as Mr. Swan informs us) may be transferred direct to cardboard, provided the latter presents a perfectly white and even surface. The mode of proceeding is as follows :—The card is placed for the period of one minute in cold water, then pressed between sheets of blotting-paper until it ceases to shine, but appears almost half dry, and the picture (previously gelatined and trimmed) laid I’.pon it; both are then placed between pieces of felt and pressed in a rolling-machine, the picture being undermost. Finally, the india-rubber paper is removed with benzol. In operating in this manner it is indispensably necessary that a good cardboard with an even surface should be employed. Both methods of transfer are, however, open to an objection. The delicate outlines of the picture are easily damaged in the event of the paper being too moist, for the gelatine gives way and the roller injures the softer details of the print. For this reason Cherrill employs a press instead of a roller, and the mode of proceeding detailed by him in a recent article I have found to answer admirably. For small pictures an ordinary copying-press will be found sufficiently powerful, but in this case the pictures must be so wet as to shine. Blotting-paper is laid upon the picture, which is allowed to remain under pressure for about four minutes, and then taken out and dried. By this means it is impos sible to damage a picture. Another interesting idea Mr. Swan has communicated to me: the picture upon the india-rubber paper is immersed completely in a warm gelatine solution of— Gelatine 6 to 8 parts Glycerine ... ... ... 2 to 22 „ Water 100 „ and when all air-bubbles have disappeared, a piece of fine tracing-paper is likewise immersed in the solution, and both are then removed, care being taken to allow them to draw over the side of the dish, in order that they may be properly drained. Both are hung up to dry, trimmed, placed upon moist cardboard, and put through the rolling-press without any fear of the print being injured by the pressure ; the india-rubber is afterwards removed with benzol. This pro cess 1 have worked with very good success. If the picture upon the india-rubber has been covered with a thick coating of gelatine (with 12 percent, of gelatine), it can be detached, after moistening with benzol, in the form of a clean film. This circumstance led me to experiment upon the feasi bility of transferring the carbon print to glass—an opera tion in which I was perfectly successful. For this purpose I coated the picture upon the india-rubber film liberally with the following solution :— Gelatine 12 parts Glycerine ... 4 „ Water 100 „ and fastened it upon a warm glass plate ; the transfer was then allowed to dry, and then the india-rubber coating removed with benzol. The picture remained upon the glass plate in the most perfect state. It is as well to coat the picture on the back, before it is dry, with a solution of— Chrome alum ... ... ... 1 part Water ... 300 parts In the same manner pictures may be transferred to opal glass, and in this form have a very pretty effect, For the enamel and porcelain processes the method is likewise suscep tible of application ; an enamel colour is mixed as the pig ment in the carbon-tissue, and by this means a transferable picture is obtained, capable of being burnt into any suitable surface. Another interesting circumstance I may here point out. In the picture upon glass we possess obviously a carbon positive, and, by a repetition of the process, a carbon negative may be obtained. Here is therefore a method of multiplying negatives, and of producing them of a more permanent character than by means of the silver process. Since writing the above, a result of some importance has been obtained in the photographic laboratory at the Royal Industrial College, which will interest those who have expe rimented with the process. One of my pupils, M. Lother, a student in the College, was proceeding in the ordinary manner to transfer to Steinbach paper several developed carbon prints upon india-rubber paper; by an oversight, he
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