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The photographic news
- Bandzählung
- 35.1891
- Erscheinungsdatum
- 1891
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- Englisch
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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. 1728, October 16, 1891
- Digitalisat
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The photographic news
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Band 35.1891
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THE COLLODIO-ALBUMEN PROCESSES. BY P. C. DUCHOCHOIS. The first collodio-albumen process was devised by Taupe- not in the hope of obtaining a more reliable and sensitive dry photo-film than those then in use (1855). Originally it consisted in coating a plate with a collodion simply iodised; then, after sensitising and a good washing, to eliminate the silver nitrate in excess with a solation of albumen, or better, of fermented albumen also iodised with one per cent, of potassium iodide, whereby the silver iodide held in the collodion film being rendered insensitive to light, or nearly so, the plate could be kept for a very long time. To excite it, it sufficed to dip for a few seconds in a bath of aceto-nitrate of silver, then to wash off the excess of this salt, when, after drying, the plate was ready for exposure. As usual, the development was effected by gallic acid solution, to which was added a little of the sensitising silver bath. This collodio-albumen film is no more sensitive than the albumen film when both hold the same silver salt. Here the writer cannot refrain to remark that it is really very strange that, having as an example the Daguerreotype process, showing that the sensitiveness of the photo-film is ten-fold exalted by silver bromide conjointly with the iodide, the inventors of all the photographic processes— calotype, albumen, collodion—prepared the sensitive film without this salt, and that most of the first photographers, following their original directions, and on the authority of the best writers—amongst them the author of “Photo graphic Chemistry ”—for a long time adhered to the simply iodised preparations. How many wrong statements which led the beginners astray were published in those early days of photography by persons who seem never to have experimented with the processes they spoke about! Has it not been said that Ferrier and Soulier albumenised the plates in purls natn- ralihus to avoid dust? And on this queer saying how many amateurs and, perhaps, professional photographers were deterred from working the best-known diapositive process? Dust is no more annoying in preparing plates with albumen than with a gelatino-silver bromide emul sion. It suffices to sweep the operating (dark) room with wetted sand, and to copiously sprinkle it, when in half an hour or one hour the room will be free from dust swimming in te air; and, as the albumenising is done by white light, any particle of dust which accidentally may fall on the film can be seen and removed before equalising the film or placing the plate in the drying box. The improved Taupenot process—that is, with an alkaline bromide added both to the iodised collodion and albumen—was a favourite among French photographers, although complicated by the preparation of the double film, until Madame Lebreton suggested the use of plain instead of iodised albumen, and to wash the excess off. The albumen is consequently employed as a preservative, the collodion photo-film remaining sensitive to light. This process gave rise to many improvements, amongst which are those of Fothergill, Maxwell Lyte, Pestcher, Mann, and Sebastian Davis, who published, in 1878, a process which we shall describe. It yields good and brilliant negatives, and can advantageously be employed to obtain diapositives for the magic lantern, &c. The process we have now to describe is a true albumen process, in which plain collodion serves as a support for the albumen film. It is not an improvement—far from it —the preparation of the plate being complicated by the previous collodionising, &c., and the double film being liable to produce certain defects. This process, I think, I have been the first photographer to devise. I was at that time (1857) in Utica, giving lessons in photography to Mr. D. D. T. Davie. He wanted to learn the albumen process in order to photograph the beautiful falls of the Black River, six in number, occupying at intervals a picturesque ravine, about two miles long, near the village of Trenton Falls, N.Y.; and from the negatives to make transparencies for the stereoscope. Not having a drying box at hand, it occurred to me to prepare the plate with a thin film of plain collodion, and, after immersing it in water until greasinesshad disappeared, to coat it with bromo-iodised albumen, &c. I succeeded well, but on many plates the film blistered badly and slipped out. The remedy was, of course, apparent. It sufficed to edge the plate, and to use a porous collodion. The pyroxyline, which always has given me excellent results in the wet collodion process as well as in the pre paration of dry plates, both by the bath or emulsion pro cess, and which I recommend for the process in question, is obtained by the formula following: — Sulphuric acid, commercial, 66° Baume ... 5 pints Nitric acid, commercial, 41° Baum ... 4 ,, Temperature, 140° to 145° Fahr. Time, from ten to twelve minutes. Cotton, as much as the solution will cover well. The pyroxyline prepared by this formula can be dissolved to the extent of more than 8 grains to the ounce of alcoholic ether (1: 1), giving a structureless, porous film, specially well adapted to hold a great proportion of silver bromide if employed for emulsion, which is indeed a great desideratum when the image is developed by the alkaline method, since the intensity depends on the layer of reduced metallic silver, which itself depends on the thickness of the silver haloid coating. For the albumen process presently described, a collodion prepared with 1 part of pyroxyline for 100 parts of alcoholised ether answers quite well. If one objects to the preparation of the pyroxyline, we recommend the photographic cotton manufactured by Charles Cooper & Co., or, in lieu, an old coloured collo dion, the iodide not interfering with the results, for it is washed off when the plate is immersed in water to elimin ate the ether and alcohol. The best protection against blisters, &c., is an albumen substratum. It is prepared by dissolving the white of one egg in a pint of water, adding one or two drams of aqueous ammonia, and filtering through paper. The modus operandi of the process is as follows. The glass plate is placed in a very strong solution of washing soda for an hour, then rubbed under the tap with a stiff brush, then well rinsed, drained, and, while wet, twice flowed over with the substratum, and lastly, placed on a rack to dry spontaneously. The plate is now coated with collodion, and, as soon as the film is set, immersed in water until the liquid flows evenly over it. It is then allowed to drain, and as soon as the collodion film is surface dry, but still damp, it is coated twice with the bromo-iodised albumen, and left to dry on a rack in a place quite free from dust. Sensitised, the plate is washed. Excessive washing considerably impairs the sensitiveness. It does not much increase the keeping qualities of the film, for albumen necessarily forms with silver nitrate an insoluble, not well
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