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The photographic news
- Bandzählung
- 27.1883
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- 1883
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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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THE PHOTOGRAPHIC NEWS, Vol. XXVII. No. 1276.—February 16, 1883. CONTENTS. . PAGE The Physical Condition of the Visible Image 97 Photo-Spectrographic Researches on Reflected Light 98 Note on Gelatino-Chloride Prints. By Dr. J. M. Eder ’’ 98 Glass 98 At Home.—Mr. Herbert Barraud in Oxford Street 100 The Forthcoming Eclipse of the Sun. By C. Ray Woods 101 Notes on Commercial Photography in the United States. By J. 102 Notes 103 PAGE Patent Intelligence 106 Twelve Elementary Lessons on Silver Printing 106 Notes on Photography. By E. Howard Farmer 107 Freeing Emulsion from Soluble Colloids. By A. Haddon 108 Photo-Micrography. By G. J. Johnson 108 Correspondence 109 Proceedings of Societies 109 Talk in the Studio 112 To Correspondents 112 THE PHYSICAL CONDITION OF THE VISIBLE IMAGE. That a great difference exists in the nature of the deposit of metallic silver produced by different developers, must be evident to a 11. It is sufficient to take but a glance at nega tives, produced from a wet plate and from a gelatine plate respectively, to notice the total difference in the appearance of thesilver image in the two cases. But while a great deal of attention has been bestowed upon the subject of dry-plate development, we do not think photographers generally are alive to the great importance of a careful study of the influence of different developers upon the physical condition of the deposit. In comparing developers, it is not enough to confine the attention solely to the brightness of the image, the perfection of gradation or freedom from stain and similar characters, although it cannot be denied that these are fundamental points which should certainly be first brought to notice. But we hear very little of the actual constitution of the image, of the size or colour of the particles, or of the amount of lateral electrolytic action. In fact, of the many who record valuable observations con cerning the efficiency of certain developers, but few com paratively submit their developed films to a searching microscopic examination. It is possible that this omission arises to some extent from a belief that the grains of silver are constituted in very much the same manner by whatever chemical process they may have been deposited. The fallacy of this idea can, however, be easily proved by any one who will undertake the following simple experiment. L it a dry plate be exposed in the usual manner, and then cut into several pieces. Let the pieces be developed by the same process, but with gradually increasing quan tities of some restraining substance, so that while the first piece undergoes rapid development, the last may require a very prolonged treatment. It will now be found that, although, to the unassisted eye, there may not be very much apparent difference between the results in each case, yet there will be striking variations in the size of the grains of silver when submitted to microscopic examination. In fact, the size of the grain varies with the length of time taken in the deposition, and it is evident that a coarser grain will give proper density with a smaller amount of reduced silver than a very fine grain would do. Now a great deal has been written about the relative values of slow and rapid development, of the impossibility to procure sufficient density with certain developing for mulae, and of the advantages and disadvantages of energetic developers. Practically, however, all these questions depend, to a large extent, upon the physical nature of the deposit, upon the minute structure of the image, which, although only to be revealed by microscopic investigation, exerts a far larger influence than is usually supposed upon the character of a negative. We repeat, therefore, that in all comparisons of different developers, the degree of coarseness of the particles of silver should be as carefully noted as any of the other characters of the deposit. An elaborate microscope is by no means necessary for this purpose ; any small pocket lens, magnifying about 30 diameters, is sufficient. Another point of no less interest at the present time is the possibility of procuring a reducing agent for silver bromide which shall deposit silver in a condition resem bling that which is obtained by the wet process. If this could be done, every objection to the use of dry plates would be finally swept away. Unfortunately, it appears that every developing agent has its own special charac teristics, and there is an a priori improbability that dry plates will ever be made to resemble wet plates in this respect. Thus alkaline pyrogallol gives a brown image, ferrous oxalate a black deposit. The double tartrate of antimony and iron gives a beautiful golden brown picture, and the ferrous phosphate imparts a brick-red colour. Negatives produced by the hydrosulphite developer seem to approximate more to the wet plate, having a greyish colour. It is interesting also to note the observations of Carey Lea on the influence of certain salts on the physical character of the developed image. Thus the addition of potassic iodide to ferrous oxalate gives a reddish tone to the finished negative, while the presence of borax imparts a weak brown tone. The presence of potassic bromide in the ferrous tartrate developer changes the colour of the image from brownish-red to olive-black. These examples are sufficient to show what apparently trifling causes are enough to change the physical character of the silver deposit. There can be no doubt also that there exists a suitable strength of developer for each kind of dry-plate and for every exposure, and that a beneficial result would, in many cases, be obtained if over-exposed plates were subjected to a less energetic reducing agent, rather than the same develo per with a large quantity of restrainer. It is stated that plates exposed ten times longer than is usually required for ferrous oxalate development may still be developed by ferrous tartrate. Finally, we come to the question of electrolytic action in development. It is evident from the experiments of several investigators that strength of image is produced by the influence of each reduced particle of metallic silver upon adjacent particles of unaltered bromide, which are thereby reduced first to sub-bromide, and finally, in their turn, to metallic silver. But this electrolytic action goes on more extensively in a downward, than in a lateral direc tion. Why this is, it is not easy to say, unless it be tha- light is able to penetrate the film at least to a degree suffit cient to cause a tottering equilibrium of the molecule forming the illuminated parts. Nevertheless, lateras action does takes place to some extent; the microscope show
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