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The photographic news
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- 27.1883
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- 1883
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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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MARCH 15 1883 I the PHOTOGRAPHIC News. 167 A purely amateur association, such as this is, scarcely num bers one interested in engraving on wood amongst its members ; hence the application of platinotype to wood-blocks will hardly prove the matter for congratulation it would be in a community of engravers. But ever since photography was first applied to wood blocks, supplanting the draughtsman’s pencil, the film or medium necessary for carrying the photographic image has proved a serious drawback and impediment to rapid and effective work. The film will often split off the block under the action of the graver just where it is most important to retain it! To sentitise a wood block, it is rubbed with a pad of cotton wool moistened with strong alcohol; the surface is then smeared over with a tuft of wool containing the sensitiser. The block is then dried, printed upon, developed, and rinsed rapidly for a few seconds in the acid bath ; it is then dried off with methylated spirit, and is ready for the engraver. The recent application of the process to textile fabrics I believe to be more important than many might suppose it to be; for, putting aside the various more or less fanciful articles which may be produced by materials so decorated, there yet remain solid worth and art-capabilities which ought to render fabrics of great value to the photographer whose ideas are not entirely guided by the fixed rules of conventionality, who is able to use discrimination, and has the courage of his convictions. In reproductions of oil paintings the result is sometimes remarkable ; the texture adds much to the effect, and to the eye of an artist considerably enhances the value of the photo graph. Photographs from nature, both portraits and landscapes, may also be most effectively printed on textile fabrics. Some portraits I have seen were exceedingly pleasing, rich and vigorous, yet in harmony and softness like a mezzotint engraving. When developing prints on textile fabrics, it is of the utmost importance to heat the bath to a temperature exceeding that neces sary for paper, in order that the reduction of the platinum shall take place as quickly as possible after contact with the fluid. The resulting image will then have a richness and “ bloom ” not obtainable by any other means. Care must be taken not to print too deeply, because a cooler bath as a means of correction of errors of exposure is scarcely desirable ; moreover, the very hot bath (say 200° Fahr.) develops detail after a shorter exposure than is necessary when a cooler bath is used. This reminds me that it is a very common fault of beginners, noticing how rapidly the image appears, to act on the supposition that the whole action is complete in “ less than no time,” and the prints are taken off the hot solution (often not hot enough) and placed in the acid bath before the shadows have had time to gather strength and homogeneity. The result is a coarse, poor print. It is well to remember that the development cannot be too long. The exposure may be too long, after which the bath may be too hot; but the best results are produced by a fully-hot bath and a properly-regulated exposure. Another important point in connection with textile fabrics is the use of plenty of acid bath, for. naturally, the quantity of iron and platinum salts, and also of potassic oxalate, transferred to the baths is much greater with these materials than is the case with the less absorbent papers. NOTES ON GREEN FOG. BY J. M. TURNBULL.* Since the general adoption of the gelatine process, there are several shortcomings in connection with it that have come prominently forward. Amongst the principal of these are frilling and green fog. I do not intend to discuss the former of these at present, as the cause of and remedy for frilling are now very well known ; but the cause of green fog being more obscure, I shall have a few words to say on what is, in my opinion, the cause of it, and the means to be taken to correct it. There have been various theories put forward within these few years, but none of them is, in my opinion, altogether correct, some of them being very wide of the mark.. I shall, however, at present notice only one of these, that of Captain Abney, t He says : 1 This fog is due to decomposed gelatine and oxidised pyrogallic acid. Green by reflected light, it is pink by transmitted light, being dichroic. This at once points to the fact that this fog is somewhat of the nature of a dye, and every oxidising agent ought to destroy it.” ".Read before the Edinburgh Photographical Society. + Photography with Emulsions,” 2nd edition, p. 227. Now with regard to the first part of this theory, that it is caused by decomposed gelatine, it is a well-known and admitted fact that decomposed gelatine is soluble in cold water, and that should there be any of it in the emulsion through being boiled, or in the gelatine itself prior to being made into an emulsion, it is entirely removed, or but very little of it is left when the emulsion is washed, so that this is not one of the causes of green fog. As a further proof of this, I have several times had quantities of emulsion standing for some weeks through want of time to coat the plates ; the gelatine then was a good deal decomposed, part of it having evenjliquefied. On adding a sufficient quantity of a strong bodied gelatine, plates coated with it turned out as fine as need be, with entire freedom from green fog and other defects. This shows that even if decomposed gelatine is present in quantity, green fog does not as a consequence result. But when a soft or partially decomposed gelatine is used, frilling will be produced, of which more hereafter. Nor is green fog caused by oxidised pyrogallol, as is easily proved by the fact that when a plate, liable to give green fog, is deve loped with sulphite of soda in the developer, which greatly retards the oxidation of the pyrogallol, green fog will be produced while the developer is still perfectly clear ; yet if the same plate were developed without sulphite, green fog might be absent. This I have no doubt is caused by the hardening action of the sulphite on the film; oxidized, otherwise discoloured pyrogallol, acts simply as a dye or stain on the film, and gives the well-known greenish yellow colour to gelatine negatives. But that this is not the true green fog is proved by the fact that this colour is discharged by immersing the plate in citric or hydrochloric acid and alum, while proper green fog is not cleared away. In the early days of gelatine emulsions, when a soft gelatine such as Nelson’s No. 1 was used almost exclusively in making emulsion, green fog was never heard of, nor would it yet be, if such a soft gelatine were still used exclusively in making plates ; but when using such a gelatine, a much worse evil than green fog had to be combatted, and this was frilling. To remedy this a harder gelatine is now used. This is no doubt an effectual remedy for frilling, but it is often used in excess, and this is what is, in my opinion, the cause of green fog. This hard gela tine gives a skinny, impenetrable film, which either the developer or fixing permeates very slowly. If we examine the colour of an ordinary bromo-iodide plate, we find that it is of a greenish yellow : if this is a hard film, as I have already spoken of, the hypo fails to get at all the unused bromide in the film, and the result is green fog. There is no doubt this species of fog can be modified more or less in the development; if, for instance, the plate be under-exposed, and the development be forced or prolonged, the maximum of fog will result, the ammonia evidently being the agent that acts most on it, the quantity of pyro, seeming to make no difference as far as the fog is concerned. To remedy, as far as is possible, in the development, the bad effect of plates giving green fog, they should be given as much exposure as is allowable, and developed with an extra quantity of bromide and pyro, and a minimum of ammonia ; or the plates should be developed with ferrous oxalate, which gives negatives free from this defect, though, in very bad cases, I have seen plates that gave green fog even with it. It is in the making of the emulsion that we must take care that green and also red fog are not produced. To make gelatine emulsion properly, it should not be made with one sample of gelatine, though there are in the market samples of gelatine which will give very fine plates. Two different kinds of gelatine should be used, one a softish kind, such as Nelson’s No. 1; this of itself is an excellent gelatine, but too soft to prevent frilling. This should be tempered with a hard sample, such as Heinrich’s, Henderson’s, or Nelson’s amber; but no more of the hard variety should be added than will just prevent frilling. This is most important, as the finest and most perfect plates are got when they are just off what I may call the frilling point. The film is then in its best condition for development; it is more porous, the solution gets quicker into it, and is therefore quicker deve loped, and consequently much time is saved, less washing is required, and there is much less danger of retaining hypo in the finished negative, On no account should chrome alum be used in the emulsion to harden the finished film, as is, I believe, often done. This is a most dangerous practice, as, when even the very softest gelatine is used, the least over-dose will make the film too hard, and also produce green fog ; all the hardening can be done with the judicious use of a harder sample of gelatine, as I have already stated.
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