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The photographic news
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- 35.1891
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- 1891
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1693, February 13, 1891
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The photographic news
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THE PHOTOGRAPHIC NEWS. 119 FEBRUARY 13, 1891.] PHOTOGRAPHY IN FRANCE. BY LEON VIDAL. New Process of Photography in Colours—Utilisation of Photography for Impressions in Colours—Sensi tised Silk— RADIGUET’s Electro Photophore—Sul phite of Soda in Development—Plates with Chloro Bromide of Silver—New Pressure Frame—Micro Photographic Slides—Direct Carbon Prints. Neio Process of Photographij in Colours.—The leading feature of the meeting of the French Photographic Society is a discovery by M. Lippmann. This scientist made a communication to the Academy of Sciences on the 2nd of February, which has since caused considerable commo tion. “ Photography in Colours,” such is the subject of this discovery. M. Janssen, president of the French Photographic Society and colleague at the Institute of M. Lippmann, brought to the meeting of the Society one of the plates shown by M. Lippmann, and, with his habitual precision, gave explanations, as complete as possible, of the phenomena serving as bases for this discovery. Let us commence by saying that M. Lippmann, after many experiments, thinks that he has succeeded in photograph ing luminous undulations in such a manner that the re production permits us to see, by reflection, red where red has fallen on the plate, yellow where yellow has acted, and so on. He appears to have succeeded in registering the interferences resulting from the meeting of rays re flected from a reflecting metallic surface and of incident rays. From this meeting there results, in the case of light, as in that of sound, intermittences of light and dark ness analogous to the alternations of sound and silence. These interferences being produced in the body, or, rather, in the thickness of a sensitive film, give rise to more or less numerous films after development, of which some are black, and others, corresponding to the obscurations, are white. Now, according to the action of the rays of different colour, the number of waves varying with the colour, it happens that the eye perceives the colour answering to each number of waves that characterise it. It is known that the length of the luminous waves is measured by millionths of millimetres. Thus the spectrum red has a wave length of 620 millionths of a millimetre. Now, supposing that the sensitive film traversed by reflected and incident rays has a thickness of one-tenth of a millimetre, there will be called forth in this film of 100,000 millionths of a millimetre 161 waves in the onedirection, and 161 waves in the other direction, from which there results a sort of interior strata of black and white films superposed, corres ponding to the succession of light and shade produced by interferences. In the same case, the violet, having the wave length of 423 millionths of millimetres, produces strata of 235 black and white films, producing to the eye precisely the effect of violet light. Experience seems to confirm this theory. M. Janssen showed a photograph of the spectrum confided to him by M. Lippmann. On examining it carefully, and making the little plate yield reflected images in different directions, we finally perceived a sort of iridescence in those parts where we were told the spectral colours existed. We only saw them very imperfectly rendered, and certainly we should never have suspected, if we had not been told of it, that it was a reproduction of the solar spectrum with the colours. Viewed as a transparency, the plate showed a reddish stain in the part corresponding to the middle of the spectrum. Theoretically, we ought to' see, as a transparency, colours complementary to those seen by reflected light. M. Lippmann operates as follows. In the first place, he covers the surface of a glass plate with a coating of albumen sensitised with iodide of silver. The plate is placed on the surface of a mercury bath arranged in a vertical camera, and the spectrum is projected upon it. The exposure lasts for from one to two hours, and the development and fixing are carried out in the usual manner. The essential precaution is to use a film as continuous as possible, as free as possible from network and granulations. Gelatino-bromide of silver emulsion is unsuitable on account of the very marked granulations of the bromide of silver. No emulsion will serve, and it is necessary to produce the substance chemically in the material serving as the colloid layer, so as to have the most continuous film possible—the least granulated that can be realised. This will be understood from what has been said above. And now what have we to conclude from this communication? I find myself absolutely embarrassed in endeavouring to form an opinion or hope in any direction. Is this a discovery conducting to photo graphy in colours? Up to the present the principle involved is so delicate, and the results so incomplete, that I can really say nothing. I must await farther and more crucial experiments before I can bring myself to believe in the possibility of finding a satisfactory solution in this direction. We do not desire to be sceptical, but we ought nevertheless to be prudent, and not to trust too readily to hopes that may very likely never be realised. It is certain that a solution, to be in the least practical, must be supported by something very different from what has been shown to me. However this may be, the fact in itself is of very great interest; it adds to our knowledge of luminous action, and the spectral embryo obtained by M. Lippmann may very well develop itself and produce a complete image of the spectrum. This is for the future to decide. Ulilisalion of Photograph!/ for Impressions in Colours.— Mr. A. Gravier presented a collection. of phototypo gravures printed in three colours, published by the Petit Journal. His object was to demonstrate the services rendered by photography, as, thanks to its aid, the original—a water-colour drawing—had been reproduced. The photograph of the picture had been made on three blocks of wood, on which the engraver had created the monochrome blocks suitable for rendering the three colours. It would, perhaps, have been better still to print from three negatives in which the selection of colours had been photographically made. The inter pretation of the subject for the engraver would certainly in this way be more complete. Sensitised Silk.—M. Tisseron has succeeded in preserving, without change, his sensitised silk. Samplesand prints in support of this statement were produced. There is nothing remarkable in the process, but it is interesting to note the possibility of preserving the silk, ready for print ing, for a long period without change. Radiguel's Electrophotophore.—M. Radiguet showed an electric lamp suitable for dark room illumination, called the electrophotophore. This apparatus consists of a bichro mate battery of three cells, connected for tension. The globe containing the carbon filament of the incandescent lamp is itself enclosed in a box fitted in front with red glass. Accordingas the zinc elements are plunged into the
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