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The photographic news
- Bandzählung
- 24.1880
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- 1880
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1140, July 9, 1880
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The photographic news
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Band 24.1880
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- Register Index 631
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Band 24.1880
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330 THE PHOTOGRAPHIC NEWS. [July 9, 1880. 9gotogragkic 3ths, Vol. XXIV. No. 1140.JULY 9, 1880. CONTENTS. page Photography In and Out of the Studio 325 A New Instantaneous Shutter. By G. L. 326 At Home 326 Aids to the Working of the Gelatino-Bromide Process. By Capt. W. de W. Abney. R.E., F.R.8 328 The Electric Shutter. By Mr. H. Darwin 328 Note on the Oxy-Hydrogen Light. By Rev. T. F. Hardwich . 329 Royal Cornwall Polytechnic Society 329 Stored-up Light as a Source of Fogging 330 Cold Emulsification 331 Notes 331 Topics of the Day 332 French Correspondence. By Leon Vidal 333 Correspondence 334 Proceedings of Societies 335 Talk in the Studio 336 To Correspondents 336 STORED-UP LIGHT AS A SOURCE OF FOGGING. More than two hundred and fifty years ago a shoemaker of Bologna made the curious observation that if barium sulphide, which he obtained by the reduction of the sul phate, was exposed to sunlight for a short time and then taken into a dark-room it evolved a considerable amount of light. After the barium sulphide had ceased to shine in the dark, it could be recharged with light by a renewed exposure to the sun’s rays, or even to diffused daylight. Subsequent investigations have shown that very many substances have the above-mentioned remarkable property of absorbing light, and giving it out in a modified condi tion after the exciting cause has ceased. This phenomenon of light-storing is known to physicists as phosphorescence ; and the number of substances possessing it in a low degree is very large. Many years after the discovery made by the Bolognian shoemaker, Canton found that an extremely powerful light magnet or phosphorus, as he termed it, might be obtained by the calcination of oyster shells with sulphur. The impure calcium sulphide thus obtained was found to emit so much light after insolation, or exposure to the sun's rays, that the light evolved from a small lump of it enabled one to see the time by a watch ; and the luminosity of the insolated calcium sulphide often lasted as long as ten or twelve hours. Daguerre was very successful in the preparation of Canton’s phosphorus, and published details of manipulation which rendered the production of an exceedingly phos phorescent product a matter of ease and tolerable certainty. He also studied the photographic properties of the phos phorescent light, and found that it acted energetically on the sensitive Daguerreotype plate, just as is the case with ordinary solar light. Experiments of an analogous nature were undertaken by Niepce de St. Victor, but although his results are of the greatest interest from a scientific and theoretical point of view, they do not appear to have led to any practical applications of phosphorescent light in connection with the photographic art. The experiments of more recent investigators prove that phosphorescence is generally excited by the violet and ultra violet rays, while the emitted light is always, or almost always, of a lower degree of refrangibility, and consequently of a more feeble actinic power. As regards the colour of the emitted light, various tints of blue, green, orange, and yellow prevail, the same body often giving different tints of light in accordance with slight variations in the details of its preparation. It is a remarkable fact that the evolution of light by phosphorescent bodies may be very rapidly brought to a termination by their exposure to the least refrangible rays of the spectrum, such as the red rays ; and some remark able results, founded on this circumstance, have recently been obtained by Lieutenant Darwin, and by Mr. War- nerke ; but as the experiments of these investigators have been recently described in the Photographic News, it is unnecessary to enter into details at present; more espe cially as our object is to point out that the absorp tion of light by many substances having only feeble phosphorescent properties, and the subsequent evolution of this light, may lead to fogging in the case of the extra ordinarily sensitive gelatino-bromide plates which are bo extensively employed at the present time. Many of the most successful workers with the gelatine emulsion pro cess fully recognize the fact that it is very undesirable to admit a full flood of white light into the dark room imme diately before darkening this apartment for the manipula tion of sensitive plates, and we have heard of numerous instances in which plates have fogged after having been placed in proximity with white or light-coloured objects recently exposed to the action of a powerful light. It is interesting to note that most phosphorescent bodies are light-coloured, so that little mischief need be appre hended from the approximation of dark-coloured bodies to sensitive surfaces, even though the dark-coloured bodies may have been quite recently exposed to the action of direct sunshine. In order to obtain some definite ideas as to the extent of the danger above referred to, we made a few experi ments with some feebly phosphorescent bodies more or less likely to be met with in the dark room, or to be brought into immediate proximity with sensitive films. Among these may be mentioned the diamond, chalk, lime, plaster of Paris, chloride of calcium, tartaric acid, sugar, silk, and paper. Two glaziers' diamonds were exposed for a few minutes to sunshine, and were then placed, crystal downwards, on the face of a gelatino-bromide plate. They were allowed to remain for ten minutes, red light being excluded during this time. On developing the plate it was found that one diamond had made an impression on the film, while the other one had produced no apparent effect. The experi ment was repeated with a piece of thin glass between the crystals and the film, and a similar result was obtained. In this case the phosphorescent diamond had a slight yellow tint, while the non-phosphorescent one was colour less. The phosphorescent diamond was again exposed to sun-light, and shut up in a dark box for one minute : being now placed on a gelatine plate, and allowed to remain for ten minutes, it was found that an impression could be de veloped by the application of an energetic developer. It was again similarly exposed to sunlight, but, instead of being placed in a dark box for one minute, it was exposed to the radiations of a red lamp for a similar period. After this it was placed in contact with a sensitive film as before, but in this instance no trace of an impression was revealed on applying the developer. In this case, then, it is evident that the red light extinguished the phosphorescence of the diamond during the minute of time during which it was allowed to act. In order to test the phosphorescent power of chalk, lime, plaster of Paris, chloride of calcium, and sugar, a kind of rough negative was prepared by gumming two strips of black paper, in the form of a cross, on a glass plate. This being placed, paper side upwards, on a gelatine plate, the insolated substance waspiled upon the paper cross. In each case some slight effect was produced, provided that the phosphorescent material had been sufficiently moved and stirred about during exposure to sunlight to saturate every part of it with light. In the case of one sample of plaster of Paris the phosphorescence was very energetic, a dis tinct impression being produced by allowing it to remain one second on the paper cross ; while in the case of the chloride of calcium and sugar only an extremely feeble image was produced, even by an exposure of ten minutes. We also tried the effect of covering the paper cross with each of the above-mentioned substances, and then allowing red light, from an ordinary non-actinic lantern, to shine on the under-surface of the plate, and it proved that five
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