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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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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 27.1883
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cut into suitable sizes, and any number of these pieces are superpcsed one upon another, the prepared side being upward, and between each piece is placed a sheet of tin foil or similar material. The papers so interleaved with metallic sheets are then pressed into a shell or matrix of any suitable curvature by a die or pressing device of corresponding curvature, which is subjected to heavy pressure, and forces the paper and tin foil or other metal into a curve. The whole is then bound around the edges, as is done with sketching or drawing-blocks or pads; the tin foil assists the paper to retain its curve, and also protects the rear sheet from light while the front one is being exposed in the camera. The paper and metal may also be made into flat blocks exactly similar to the ordinary drawing blocks. Our object in bending or curving these tablets is that, when they are placed in the camera in position for exposure, they have the same centre as the curved surface of the lens, and by this means per fect equality of illumination is obtained over the whole surface. The lines are absolutely straight, and the definition is more clearly defined, and many more technical advantages are secured well known to the profession. The use of stops or diaphragms (if these are not entirely dispensed with) is considerably modified. The tablets are placed in the dark slide and exposed in the same manner as an ordinary sensitive plate. After exposure, the exposed sheet is detached from the block, and developed in the usual manner. The surface to which the picture is to be trans ferred should be previously prepared by brushing over the same a solution of gelatine and alum, and allowed to dry. The picture, while still wet, is pressed in contact with the surface, to which it firmly adheres, and, when dry, the paper may be stripped off, leaving the picture. The principle of curvature will also be found of great service in the process of enlarging, where it is desirable to obtain absolutely straight lines. The picture having been produced on the paper, can be transferred to a curved glass by the process above described, and the picture can be made to face either side by attaching it to the concave or convex surface. For magic lantern slides or discs our inven tion is very advantageous, as pictures taken on the curved paper are transferred to curved glass, and, when thrown on the screen, will be found to cover the whole disc of light with per fect definition up to the edges. In transferring or reproducing the pictures taken upon such paper, although we do not use glass in the production of the negative on the transfer paper, we have transferred it to glass in order to print therefrom in the usual manner. The negative has then been reversed, and has again to be transferred for most ordinary purposes of printing. We find, however, that the weight of the glass would be a serious burden to travellers or those working away from home ; and its liability to breakage is also much against its use. The double transfer necessary when glass is used is also found to be tedious and delicate. We, therefore, according to another part of our invention, provide means whereby we entirely dispense with the use of glass in any part of the production of the negative, by substituting for glass a gelatino-bichromatised transparent, insoluble film, which, in addition to its advantage over glass in respect to lightness, cost, and non-liability to breakage, obviates the nesessity for a double transfer as above explained. The thinness of the gelatine film allows the negative to be printed from either side, which is a very great advantage, when required for the purposes of mechani cal printing, photo-lithography, maps, charts, and the like. We prefer to make the gelatino, bichromatised, transparent films above mentioned in the following manner—that is to say, we make a solution consisting of thirty grains of best transparent gelatine, five grains of bichromate of potash, thirty minims of fresh ox-gall, and one ounce of water. We warm the whole of these ingredients to a temperature of about 150° Fahr., and stir until the gelatine is dissolved. We then take a piece of highly- polished glass or other substance, and having previously con verted it into a dish by pasting slips of paper around the edges, we place it upon a levelling stand or perfectly level bench, and pour in the gelatine solution to any desired thickness. As soon as the solution is set, the whole is set up to dry either naturally or by artificial heat in a well-lighted room. We then wash out the bichromate salt, and again allow the gelatinous composition to dry ; after which it is stripped from the support, and is ready for use in lieu of glass plates.—Provisional Protection only. Patents Granted, in Prance. 149,685. Nieubtadt, for “A method of etching by direct im pressions, and of obtaining indelible metallic deposits on polished metal surfaces.”—Dated 20th June, 1882. Class 17. 149,778. De CHALIGNY CHAIE and Durand, of Lyons, for ‘ ‘ Improvements in the photo-nature process.”—Dated 24th June, 1882. Class 17. 149,836. HERMAGIS, for “Diaphragm slides and shutters for photographic object-glasses.”—Dated 29th June, 1882. Class 17. NOTES ON PHOTOGRAPHY. BY E. HOWARD FARMER. Lecture VIII.—The Gelatine Process—Continued. THE PHOTOGRAPHIC PROPERTIES OF SILVER CHLORIDE, BRO MIDE, AND IODIDE IN GELATINE. Silver Bromide.—The photographic properties of this substance vary very much according to what physical condition or state of aggregation it is in, its modifications in this respect being very numerous. If solutions of silver nitrate and a soluble bromide con taining gelatine be mixed with proper precautions, the silver bromide formed first appears as an opalescence, the particles being in the finest possible state of division, and if examined by transmitted light appear of an orange colour. Plates prepared with the silver bromide in this condition are of excellent quality, but very slow. If, how ever, this orange modification be digested or heated with an excess of soluble bromide or other solvent, the molecules of silver bromide gradually agglomerate, forming larger and larger particles as the heating is prolonged; at the same time, and dependent on this increase in size of the particles, the silver bromide increases rapidly in sensitive ness. This double change continues until the particles attain a diameter of about 5066 of an inch (Eder), and become some twenty times as sensitive as the orange bromide. This experiment illustrates how greatly the physical condition of the silver bromide influences its sensitiveness. Dr. Stas, who first studied and minutely described these modifications of silver bromide, divides them into three principal kinds (specimens shown) viz. :— A. Flaky bromide of silver. B. Powdery bromide of silver. C. Granular bromide of silver. Granular bromide of silver is far more sensitive than the other modifications, and forms, in conjunction with gelatine, the most sensitive substance for receiving a latent image yet known. It is described by Stas as an extremely fine dust, having sometimes a matt and sometimes a glossy yellowish white appearance. Boiled with water it remains wholly in suspension, colouring the water white. It is this granular silver bromide which is formed when the orange modification is heated as described, and also by the other methods which are employed for preparing very sensitive emulsions. These different modifications also vary in their sensitive ness to different coloured lights and behaviour in develop ment ; the extremely fine orange bromide is practically insensitive to red, orange, and yellow light, while the granular bromide is sensitive to all these colours, although much less so than to blue light (Abney) ; hence the necessity for such care (as regards the light employed) in coating and developing rapid bromide plates. The action of developers seems to be proportional to the size of the particles of silver bromide, for while the finest possible orange bromide will stand a very powerful developer with out fogging, as the particles become larger, so the tendency to reduction and necessity to restrain the developer increases till finally, when they get larger than the granular modification, they are reduced without pre vious exposure to light, and hopeless fog occurs. It is very important to remember that all these modifications have the same composition—/, e., they all contain silver and bromine only, and united in the same proportion by weight. CAUSES WHICH INFLUENCE THE SENSITIVENESS OF SILVER BROMIDE IN GELATINE. a. State of Aggregation.—This is the most important
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