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The photographic news
- Bandzählung
- 24.1880
- Erscheinungsdatum
- 1880
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- Englisch
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- F 135
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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. 1138, June 25, 1880
- Digitalisat
- SLUB Dresden
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Zeitschrift
The photographic news
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Band
Band 24.1880
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- Register Index 631
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Band
Band 24.1880
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302 THE PHOTOGRAPHIC NEWS. [June 25, 1880. Et 2ome, MR. J. W. SWAN, AT NEWCASTLE-UPON-TYNE. Many of our readers will envy us an afternoon spent in Mr. Swan’s laboratory, but we will do our best to share the benefit of it with them. Mr. Swan has always been a pioneer in photography, and where he does not originate, he makes such sound improvements, that he never fails to leave his mark upon any branch he has to do with ; and there are few branches to which he has not given attention. The names of carbon printing and Swan are synonymous ; and if the photo-relief process had not been so timely secured to himself by Mr. Woodbury, the eminent Newcastle che mist would have made it his own. Mr. Swan preceded Baron Von Lenk by some years in the manufacture of gun cotton from "slobbings and rovings ” instead of from cotton wool, for soon after the Exhibition of 1851 Mr. Swan com menced to prepare pyroxylin from this description of cotton, and has continued to do so for collodion making ever since. When the news was flashed from America twelve months ago that Mr. Edison had at last found out the way of light- ing up our dining rooms and libraries with electricity, by the simple expedient of rendering incandescent a tiny horse shoe of carbonised paper, it was found that Mr. Swan, quietly working in his laboratory at Newcastle, had made the discovery some time before, and, moreover, had taken the precaution to patent it. He has now gone far ahead of his American confrere. We passed the other evening in Mr. Swan’s drawing room lit up by electricity. A tiny glass drop, which was no other than an exhausted bulb, depended from two electric wires in the centre of the room ; the wires passed into this vacuum, and a little loop of carbon thread therein—for all the world like a bit of horsehair—became incandescent, furnishing a light so soft that it could be stared at with impunity. A petroleum lamp and a candela- bria in the same room did not even look yellow, so mild and subdued was the luminous carbon. We measured its lumi nosity, and found the same to be equal to fifty candles, and afterwards, placing it within ten feet of a model, secured a photograph in the camera with an exposure of one second. As Mr. Swan has of late occupied himself with the pre paration of gelatino-bromide, it goes without saying that he has made himself master of this new and delicate branch of photography. At the same time Mr. Swan is no enthusiast; on the contrary, he is somewhat sceptical upon the matter of new phenomena, and is more likely to disbelieve than to adopt a novel dictum. If you propound a theory in development or express a belief in the special treatment of a film, he puts his hands behind him, and permits you the privilege of demonstrating the fact yourself, placing apparatus and chemicals at your disposal for the purpose. If you succeed, well and good ; if you fail, he does not con gratulate himself upon his foresight, but, like a generous foe, straightway proceeds to help you, repeating the experiment himself, to be quite sure that nothing has gone wrong, and that the theory expressed shall, at any rate, haveevery chance. The matter of development in the light, or rather com mencing the development of a gelatine film in the dark, and continuing the operation in subdued light, did not answer in Mr. Swan’s hands, for half of the plate which had been treated entirely in the dark proved, on careful comparison, i the better and brighter. At the same time, he was ready to admit that in the case of a comparatively slow plate, and under the action of very subdued light, a gelatine film, especially in the non-actinic oxalate developer, would not be likely to suffer to an appreciable degree. Mr. Swan, in the manufacture of his plates, fully believes in the addition of a small proportion of iodide. We men tioned the opinion of several photographers who were un able to detect any difference between a film prepared wholly with bromide and one containing a proportion of iodide. Said Mr. Swan, you must be quite sure that there is iodide of silver in your plates before you make comparison ; it is possible to employ an iodine salt when making your emul sion, and yet not form any iodide of silver, or, at any rate, get any of it in the finished product. But whether there is iodide present or no, is soon apparent on taking the films intodaylight. “In this case you have only bromide of silver present,” said Mr. Swan, showing us a series of plates of a pale primrose colour, which, when held up against the ligbt, could scarcely be called opaque ; “ while here, again, this brimstone colour proclaims the presence of iodide of silver.” These latter films were quite opaque, and this test, therefore, we commend to our readers as one that is likely to stand them in good stead. The plates must be examined as soon as they are brought into the light, as their tint changes after exposure for a minute or two; and in judging their colour look at, and not through, the films. The presence of iodide, therefore, from the fact that it gives a more opaque film, and thus prevents blurring, is an undoubted advantage, while for the same reason it adds vigour to the image. Mr. Swan also believes that the ad dition of iodide is of value in contributing towards clear shadows and vigorous high lights. As to the quality of the bromide formed and the nature of its particles, whether coarse or fine, of which we have heard a good deal of late, Mr. Swan has no hesitation in saying that the coarser the particles, the more sensitive is the bro mide. Moreover, he believes that the colour seen, when viewing a glass plate coated with emulsion, as a transpa rency, is not due to the emulsion itself, but simply to the passage of light between the particles ; that is to say, when the particles are fine, the light transmitted appears to be orange or red ; while if the bromide particles are of a coarse nature, the light transmitted is grey or blue. Notwithstanding the greatest care in emulsifying and preparing the plates, Mr. Swan finds it impossible to con trol the sensitiveness within certain limits, and for this reason he adopts the common-sense plan of carefully testing the plates by a standard after the emulsion is made, and recording this sensitiveness. In this way he knows what he has made, if he does not know how he has made it. Every batch of plates is tested for density, sensitiveness, frilling, and spotting. The plates after coating are permitted to set —under an hour is the time necessary—and then dried in an atmosphere very slightly raised (between 70’ and 80° Fah.) for a period of twenty-four hours. They are then packed, not only with a view to shelter them from light, but also from that arch-enemy to gelatine, damp (the packing we need not describe, as any purchaser of the plates can examine it for himself), and they then come before the inspector. One assistant is engaged on no other work but that of inspection, and it is his duty to take haphazard a per centage from every batch for trial. The plate is put into a printing frame under a standard negative of known intensity, at a distance pre cisely of ten feet from an ordinary fish-tail gas-burner. A standard developer is employed, and a sand glass that runs exactly three minutes and a half serves to fix the time for the plate to remain in the developer. With these fixed con ditions, the sensitiveness of a batch of plates is soon deter mined approximately by an experienced assistant, and he then decides whether the plates are 5,10, 15, 20, or 25 times quicker than wet collodion, information that is at once marked outside every packet of the batch. In respect to fixing, Mr. Swan makes a point of it that gelatine negatives should be permitted to remain in the hyposulphite bath not less than an hour, for the film is so much less permeable than one of collodion ; while a correspondingly long time is necessary for its sojourn in water afterwards, to allow the gelatine to discharge the salt perfectly. Mr. Swan showed us an interesting series of negatives illustrating the effect of strong and weak developers, and the influence of varied intervals of development, in order to prove the control that may be exercised in coping with under-and over-exposed films. His normal developer in this case was six grains of ammonia and six grains of
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