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The photographic news
- Bandzählung
- 29.1885
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- 1885
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- Bandzählung
- No. 1385, March 20, 1885
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The photographic news
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Band 29.1885
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THE PHOTOGRAPHIC NEWS. Vol. XXIX. No. 1385 March 20, 1885. CONTENTS. PAGE Lecture on “Recent Improvements in Photographic Deve- lopment 177 On Brom in e- A bs orbing Power of Various Bodies 178 French Correspondence 178 The Retina of Science. By Dr. T. Charters White 179 Producing Floral Borders to Vignette Portraits. By R. Stan ley Freeman 180 Aids to Correct Exposure, By W. Goodwin ISO Notes 183 PAGE The Faculty of Observation, or Commonplace Knowledge in Picture-Making. By A. B. Stewart 1S1 Lessons Derived from Pin-hole Photographs. By Barnards. Proctor 182 Patent Intelligence 185 A Few Stray “ Shots ” in Ireland. By Adolph W. Beer 187 Correspondence—Proceedings of Societies 188 Talk 190 Answers to Correspondents 192 LECTURE ON “RECENT IMPROVEMENTS TN PHOTOGRAPHIC DEVELOPMENT.” On the 12th March Mr. W. K. Burton read before the Society of Arts a paper bearing the above title. The chair was occupied by Captain Abney, and although the lecture was nominally on “ recent improvements,” abetter title would probably have been recent modifications, inas much as the lecturer stated his opinion that, siuce 1861, when the possibility of the true development of the haloids was discovered, there had been no improvements. He qualified his statement, however, by adding that he referred only to the every-day work of developing nega tives, not to special work for which other developers than the alkaline pyro were preferable to it. To those who have but recently joined the photographic ranks, and who have not studied the history of their art, it may not be known that up till the year 1861 the possi bility of acting directly on the haloids of silver by a deve loper was not established. In the wet process, which may be taken as typical of many, the film consisted of silver haloid suspended in collodion, and the light impression was received by this film ; but the visible image was not developed in it, or from the silver in it. The silver which went to build up the image was reduced from free silver nitrate, which existed as excess on the wet plate. The diy plates of these days consisted of films—mostly of collodion—precisely similar to wet plates, except inas much as the free silver nitrate was carefully washed out of them, after which they were treated with a preservative, and were then dried. Before development, however, the free silver nitrate was always replaced. In 1861, however, Mr. Wharton Simpson read a paper before the North London Photographic Association,* in which he described a set of experiments made on dry plates which had been completely deprived of all free silver nitrate, aud subsequent treatment with iodide of ammonium, followed by a second washing. These were developed with a neutral solution of pyro, a thin image resulting, which was intensified with alkaline pyro and silver nitrate. Air. Simpson attributed the discovery of this direct development of the haloid to Mr. Mudd, who, in his turn, gave the entire credit of the suggestion to his assistant, Mr. Wardley. In the discussion which followed Mr. Burton’s lecture, Captain Abney stated it as his experience that a truly neutral solution of pyrogallol would not develop an image on a haloid of silver film. Recent experiments which we have made tend to confirm that at least in the case of gelatino-bromide plates, as with these we have given very protracted exposures behind negatives—up to a hundred times normal—and have been unable to get a trace of an * PIOTOGRAPHICNEws, 1861, p. 518, image after a very prolonged development with a perfectly neutral solution of pyrogallol. The addition of a trace of alkali resulted in the case of the very long exposures in thin, but quite complete negatives. It must be borne in mind, in connection with the ex periments of 1861, that the point towards which all atten tion was directed was the complete illumination of free silver nitrate, and that, although it was stated that the solutions were made with pyro without the addition of an acid restrainer, no particular effort appears to have been made to secure absolute neutrality. The novel feature was development without silver nitrate, not development with out alkali. It is therefore quite possible that slightly alkaline solutions were used. However this may be, the experiments referred to were the immediate forerunners of the discovery of development with alkaline pyrogallol. All will agree with the lecturer that this discovery was the greatest advance made in the matter of the development of the photographic image since the introduction of acid pyrogallic developer. Without it the dry plate process of the present day could not have been the thing it is—the negative photographic process. From the time of the discovery of the “ alkaline pyro ” developer, the lecturer passe 1 on to the announcement by Mr. Carey Lea, in 1877, that although protosulphate of iron would not develop an image in films of the silver haloids, various organic salts of iron would, and that of these one of the most useful is ferrous oxalate. In this connection it was mentioned by the chairman that the protosulphate of iron would develop a latent image on the haloids of silver if it were present at the time of exposure. Mr. Burton stated his preference for the “ alkaline pyro developer,” “ his own favourite,” to any of the organic irou developers. We do not wish to enter into the ques tion of the excellencies of pyro development “ as set against those of iron development,” but would point out that, whatever advantages the former may have over the latter for negative work in gelatino-bromide, the intro duction of the organic iron developer has opened the way to the working of certain modern processes almost as certairdy as alkaline pyro opened the way to the working of modern dry plates. We need merely mention gelatino- bromide paper as used for enlargements, gelatino-chloride plates, and the new rapid printing piper. At the lecture referred to, a series of transparencies was shown. These were all taken from one negative with the same exposure. They were developed with various deve lopers, amongst these being ferrous-oxalate, hydrokinone, and pyrogallol in conjunction with various alkalies. We weic glad to observe, in connection with the last- mentioned developers, that the lecturer entered a mild protest against those who talk about a particular alkali as giving, in conjunction with pyrogallol, a result totally
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