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The photographic news
- Bandzählung
- 27.1883
- Erscheinungsdatum
- 1883
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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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- SLUB Dresden
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Zeitschrift
The photographic news
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Band
Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
- Ausgabe No. 1270, January 5, 1883 1
- Ausgabe No. 1271, January 12, 1883 17
- Ausgabe No. 1272, January 19, 1883 33
- Ausgabe No. 1273, January 26, 1883 49
- Ausgabe No. 1274, February 2, 1883 65
- Ausgabe No. 1275, February 9, 1883 81
- Ausgabe No. 1276, February 16, 1883 97
- Ausgabe No. 1277, February 23, 1883 113
- Ausgabe No. 1278, March 2, 1883 129
- Ausgabe No. 1279, March 9, 1883 145
- Ausgabe No. 1280, March 16, 1883 161
- Ausgabe No. 1281, March 22, 1883 177
- Ausgabe No. 1282, March 30, 1883 193
- Ausgabe No. 1283, April 6, 1883 209
- Ausgabe No. 1284, April 13, 1883 225
- Ausgabe No. 1285, April 20, 1883 241
- Ausgabe No. 1286, April 27, 1883 257
- Ausgabe No. 1287, May 4, 1883 273
- Ausgabe No. 1288, May 11, 1883 289
- Ausgabe No. 1289, May 18, 1883 305
- Ausgabe No. 1290, May 25, 1883 321
- Ausgabe No. 1291, June 1, 1883 337
- Ausgabe No. 1292, June 8, 1883 353
- Ausgabe No. 1293, June 15, 1883 369
- Ausgabe No. 1294, June 22, 1883 385
- Ausgabe No. 1295, June 29, 1883 401
- Ausgabe No. 1296, July 6, 1883 417
- Ausgabe No. 1297, July 13, 1883 433
- Ausgabe No. 1298, July 20, 1883 449
- Ausgabe No. 1299, July 27, 1883 465
- Ausgabe No. 1300, August 3, 1883 481
- Ausgabe No. 1301, August 10, 1883 497
- Ausgabe No. 1302, August 17, 1883 513
- Ausgabe No. 1303, August 24, 1883 529
- Ausgabe No. 1304, August 31, 1883 545
- Ausgabe No. 1305, September 7, 1883 561
- Ausgabe No. 1306, September 14, 1883 577
- Ausgabe No. 1307, September 21, 1883 593
- Ausgabe No. 1308, September 28, 1883 609
- Ausgabe No. 1309, October 5, 1883 625
- Ausgabe No. 1310, October 12, 1883 641
- Ausgabe No. 1311, October 19, 1883 657
- Ausgabe No. 1312, October 26, 1883 673
- Ausgabe No. 1313, November 2, 1883 689
- Ausgabe No. 1314, November 9, 1883 705
- Ausgabe No. 1315, November 16, 1883 721
- Ausgabe No. 1316, November 23, 1883 737
- Ausgabe No. 1317, November 30, 1883 753
- Ausgabe No. 1318, December 7, 1883 769
- Ausgabe No. 1319, December 14, 1883 785
- Ausgabe No. 1320, December 21, 1883 801
- Ausgabe No. 1321, December 28, 1883 817
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Band
Band 27.1883
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THE PHOTOGRAPHIC NEWS. [JANUARY 26, 1883. 50 EaIaTMMMMM | horizontal position till the film was set. By a motion of a treadle each plate as it is coated is pushed on to a couple of pegs of this rack; the rack is then raised an inch or two, when another couple of pegs are brought into position for another plate. Mr. A. Cowan improved on this machine by the simple device of causing the plates to travel along a distance of ten or twelve feet on parallel horizontal rails. By this means the films, by the time they reach the racks, are set, and consequently it is not necessary to have tbe racks with absolutely horizontal pegs. We illustrated and described Mr. Cobb’s machine as modified by Mr. Cowan in the News some time ago. It is applicable either to hand or machine- coating. wood, and is given in the same manner as in the case of a foot lathe ; that is, by a treadle, flywheel with cranked axle, and a small pulley on the spindle of the roller. The direction of the motion is the same as in a lathe ; that is to say, the top part of the roller is continually moving towards the operator. Of course the revolving roller carries with it a film of emulsion. Each operator sits in front of a machine. She has at her left-hand side a pile of the plates to be coated, and on her knees keeps a cloth. A plate is lifted from the pile by the right hand by means of a pneumatic holder, and is passed rapidly over the roller, the motion of the plate being towards the advancing film of emulsion. A single drop of emulsion generally runs on to the back of the plate when it is being turned from face downwards to face upwards. This is wiped off on the cloth which the operator keeps on her lap. The plate is rapidly rocked for about a second, when it is deposited on the level table, and slid over to the other side, when, after it has laid for a few seconds to set, it is examined, and if found satisfactory is racked for drying. If any inequality of coating or other defect is noticed, the plate is put on one side, and the film is at once scraped off, to be mixed with the other emulsion. The process is performed with extreme rapidity ; and. although the skill required is not so great as for rapid hand-coating, yet there is evidently considerable knack in working quickly. The film given is—except in the case of an occasional plate, which, as mentioned, is at once rejected—absolutely even, and is as thick as there is any necessity for. In machine-coating, as in coating by hand, much depends on the method of cleaning the glass, and on the emulsion used. The glass must be thoroughly polished, and the emulsion must be of the nature which will flow well, and must, moreover, not be so transparent as to require a very thick coating of the plates, because, in the case of machine-coating, especially where the plates are held face downwards, the limit of quantity which can be made to adhere to the glass is sooner reached than in hand-coating. In fact, we believe that many who have tried machine-coating have given it up because they found it impossible to get films thick enough; the fault in reality, probably, being more in the emulsion than in the machine. It is impossible to coat with a machine at quite so low a temperature as can be done by hand. Some imagine that advantage is to be gained by coating at a temperature only just over the melting point of the emulsion ; and certainly with some emulsions this holds true, as a matt surface is gained when low temperature coating is resorted to, whilst the so objectionable glazed surface results from a high tem perature. This is to a certain extent true of all emulsions, but the limits of temperature vary much. Thus, apart from treatment, if an emulsion contains the proportions of con stituents mentioned in our last article on plate-coating, a glazed surface or film will not result till a comparatively high temperature is reached, probably about 150° Fahr. The objections to too high a temperature are always great. Besides the glossy surface mentioned, there is difficulty in getting enough emulsion to remain on the plate, whether hand or machine-coating be in use. In the case of hand coating, a very hot emulsion darts over the edge of the plate the moment it is poured on ; in machine-coating the result is a thin and uneven coating. Whilst on the subject of machinery for facilitating coating of plates, we must not omit mention of racking machines. These are constructed to do away with the labour of placing the plates in racks, and also of the possible danger to the films which there must always bo when they pass through the hands of an additional operator. Mr. W. Cobb, we believe, constructed the first racking machine. His racks were constructed of metal pegs let into a base-board, so that when the latter was vertical, the pegs were horizontal, and a plate laid on them would remain in a MESSRS. MORGAN AND KIDD’S IMPROVEMENTS IN THE MANUFACTURE OF GELATINO- BROMIDE PAPER, ETC. Last week we published a specification in which the above- named gentlemen detail certain improvements in relation to gelatino-bromide paper for positive printing, and the practical photographer will be able to gather many hints from a careful perusal of the specification in question. As provisional protection only was obtained, the improvements are now open to the public. The first suggestion—that of removing traces of lime or other impurities from the paper by means of a bath of sulphuric acid—we regard as trivial and wholly unnecessary, as papers of almost chemical purity can now be readily ob tained in the way of ordinary trade. The next point at issue—the coating of the paper with a preliminary coating of enamel—we regard as a matter of very considerable im portance, and we have already recommended this course to our readers. Messrs. Morgan and Kidd, who use the ordin ary vague language of patentees, speak of an emulsion of ground asbestos, china clay, or other substance of a similar nature, being incorporated with a solution of gelatine, starch, gum, or alum ; but we prefer to use an emulsion of barium sulphate in gelatine, a trace of chrome alum being present in order to render the film less subject to be softened or dissolved when subjected to the action of aqueous liquids. Such an emulsion is easily prepared by dissolving equivalent proportions of barium chloride and of sodium sulphate in separate quantities of a 15 percent, solution of gelatine, and mixing them. When set, the emulsion should be thoroughly washed in order to remove all traces of the sodium chloride formed by double decomposition. When this emulsion is re-melted and ready for use, a thirty-grain solution of chrome alum should be added, a few drops at a time, until indications of coagulation become noticable ; the addition of a moderate proportion—say a quarter of an ounce to each pint —of glacial acetic acid now serves to restore the gelatinous mixture to its original fluidity, and the paper may be coated. We need say nothing about the mechanical details of the methods of coating, as our readers are already well posted up as regards this point. As soon as the preliminary coat ing is dry, and all acetic acid is consequently dissipated, the chrome alum again exerts its power of tanning the gelatine, the coating becoming sufficiently insoluble for the reception of the second or sensitive preparation ; but the suggestion of Messrs. Morgan and Kidd to heavily roll the paper at this stage may be carried into practice. A second coating of the preliminary enamel is seldom or never required, if care be taken to make use of a moderately dense preparation in the first instance. If the enamel is polished over its surface with beeswax or paraffin wax, as described in the specification, it becomes practicable to transfer the resulting picture from the paper to glass, porcelain, wood, or other rigid material; but the presence of the wax interferes seriously with the process of coating with the sensitive emulsion. The making up of sheets into compact blocks, like the ordinary blotting pad, is referred to by Messrs. Morgan
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