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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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- Wahlperiode
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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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JUNE 25, 1880-1 THE PHOTOGRAPHIC NEWS. 303 NEGATIVES MEANS OF of silver plate hundred times The next " At Home ” will be “ M. Liebert, in the Rue de Londres.” THE PRODUCTION OF DUPLICATE WITH GELATINE EMULSION BY SOLARISATION. Dr. J. M. Eder writes :—When a bromide is exposed a hundred times or several Swan’s own preparation, and has been made especially for his plates. There is a tap and sink in one of the cupboards, and some big porcelain trays with hyposulphite and alum con veniently at hand. You have simply to turn the keys of the two doors and lower the gas, and you are in a dark room that is by no means dark. But with his very sensitive plates, Mr. Swan has to take care, and therefore he has his developing dishes provided with covers, which are employed as frequently as possible. In respect to the gelatine which is most suitable to the preparation of plates, Mr. Swan agrees with the opinion as expressed in these columns a few weeks since. He does not mind gelatine that is a bit turbid ; in fact, he does not lay much stress at all upon this quality, so long as the material is otherwise sound. But he will have nothing to do with gelatine that contains traces of acid, no matter how transparent it may be. Mechanical tests, or its capacity for absorbing water, are not gone into, but, on the other hand, no sample is approved until it has been actually tried for emulsion making. Mr. Swan’s extensive premises in Mosley Street, which were utterly destroyed some months since by a disastrous fire, are being steadily re-built; and we embraced the opportunity of visiting the spot. Despite the advent of gelatino-bromide, the demand made upon Mr. Swan just now for collodion is, curiously enough, much greater than for some years past. There is usually a stock of this mate rial, to the amount of from three to five hundred gallons, upon Mr. Swan’s premises, for he has great faith in per mitting it to stand several weeks before decantation ; but, fortunately both for Mr. Swau and the city of Newcastle, the fire did not attack this portion of the premises. Only sufficient for the day’s packing is brought into the central premises, and in the packing room there is not a single gas-burner, the lamps being fixed outside the windows. Nay, more, to prevent any injury that might arise from fumes of collodion escaping, the packing and store' rooms are made pretty well air-tight, and are, moreover, carefully cut off from the rest of the building. longer than is necessary to give a good negative picture, and when it is afterwards developed, it will be found that the parts of the image where the light has acted most intensely will develop very thinly and slowly, while the shadows, in which the light has not acted so freely, will develop more vigorously and more intensely. Bromide of silver which has become solarised by long and excessive exposure develops much more slowly than the bromide exposed for the ordinary time. This same phenomenon will be observed in the case both of collodio-bromide and of gelatino-bromide. If a gelatine plate be exposed for a few seconds under a negative to diffused daylight, an ordinary positive will be produced after development; but if the exposure be con tinued longer (say upwards of half a minute) the plate will be much fogged, becomes partially solarized, and appears to be in a state of transition from a positive to a negative. The transparent parts will already have a negative appear ance, while the opaque spots still remain positive. With a longer exposure the change to a negative becomes still more complete, and after from three to four minutes, about the time necessary to expose a carbon print, the transformation will have been quite accomplished. The different parts of the image on the plate appear to be solarised to various bromide dissolved in one ounce of water on the one hand, and on the other, pyrogallic acid dissolved in one ounce of water in various quantities. Thus we saw plates (all with the same exposure) developed with half a grain, a grain, and two grains of pyrogallic acid, and further examples showing the effect of these developers after an interval of two minutes, three minutes, and six minutes. Mr. Swan believes that many failures in development are due to employing ammonia of not sufficient strength, and pyrogallic acid not freshly prepared. The whole formula obviously is deranged if attention is not paid to these details. As our readers know very well, Mr. Swan recommends the employment of bromide of potassium for retarding the developing action when oxalate is employed, the bromide solution being usedin the same way as when alka line pyrogallic acid development is undertaken. Our readers know, too, that Mr. Swan has of late applied the gelatino-bromide to opal plates, but they are probably un aware that he has successfully applied it to paper. We may, therefore, expect shortly to have rolls of the sensitive mate rial supplied us for positive, and perhaps negative work, in the same way as M. Warnerke was wont to provide us with collodion tissue. But Mr. Swan has hardly got so far at pre sent, and the sensitized paper he shows us now is adapted more especially for positives printed direct or enlarged. He places a piece of this paper under a negative, exposes it for ten seconds at a distance of ten feet from a fish-tail burner, equal to one-tenth part of a second, it must be remembered, at one foot from the source of light. In developing upon opals or paper, only the oxalate solution can be employed, for there must be no suspicion of brownness in the finished result. Mr. Swan puts a little bromide solution into his bath, for in the case of positives it is necessary that the development should not be hur ried. The picture appears gradually, and in about four minutes it is satisfactorily developed. It is the most rapid printing that can be conceived, and in the case of enlargements this gelatino-bromide paper will be exceed ingly useful. The picture printed in our presence had almost an enamelled appearance, so soft and transparent were the details. An Argand burner or petroleum lamp would give sufficient illumination for making enlargements in this way; the image being simply projected magic lantern fashion upon a wall covered with a sheet of this paper; an exposure of a few seconds would suffice. As to toning, gold must not, of course, be made use of, on account of the gelatine; but there are several means of modifying the colour of the impression, if that developed by ferrous oxalate is not approved. Treatment with bi chloride of mercury, followed up by washing with ammonia, and a second application of the bichloride, gives a brown tone that is far from unpleasant. In removing the film from a gelatine plate, when such a thing is desired, Mr. Swan has recourse to the employment of methylated spirit for hardening ; that is to say, when the film has been alumed and floated off by the applica tion of a little very dilute hydrochloric acid, he toughens and contracts it again by immersion in spirit, when the film may be handled without much fear of the conse quences. Whether the operation can be done in the case of paper remains to be seen. Mr. Swan’s laboratory is an affaire de luxe', it opens into a glass corridor, at the one end of which is a dark closet, and at the other a fine glazed studio. The labora tory is a most agreeable apartment, being, in fact, Mr. Swan’s library, which is converted by very simple means into a dark room. 1’he two doors are provided with strips of list, and with mats fitting into the threshold, so that no light passes them. The large window is covered with a four-fold thickness of orange paper, and the lights of the gaselier—with the exception of one jet that is urne d.up now and then for testing—are provided with ru iy chimneys. The orange paper, by the way, is of Mr.
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