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The photographic news
- Bandzählung
- 13.1869
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- 1869
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- Bandzählung
- No. 540, January 8, 1869
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Zeitschrift
The photographic news
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Band 13.1869
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- Register Index To Volume XIII 629
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Band 13.1869
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January 8, 1869.] THE PHOTOGRAPHIC NEWS. 15 appeared in the liquid; it was slowly evaporated, and yielded pearly monoclinic crystals, to which the author assigns the singu lar formula— (CS)"H 4 N,) (CS)" H. N, Au ci J When the gold solution was employed in excess a very unstable compound was produced, which appeared to differ from the former one in containing only 1 equivalent of the urea, and 2 of chlorine. Silver Compound.—The action of nitrate of silver on the urea yielded silky crystals having the formula— 2[(CS)" H N,] Ag,0 + 4H,0. This compound is decomposed by heat with slight explosion, sulphide of silver and a crystalline sublimate being formed. When sulphur urea and hydrate of silver are heated with a little water for half-an-hour, sulphide of silver is formed, and the urea is converted into ordinary urea— (CS)" H, N, + Ag.,0 = (CO)" H, N, + Ag.S. It is, therefore, probable that in the little-known process for the preparation of carbamide by the action of oxide of silver on sulpho cyanate of ammonium, there are really two stages—one in which sulphur urea is formed, and one in which it is converted into ordinary urea and sulphide of silver. PERMANENCY IN CARBON AND SILVER PRINTS AND MODES OF TESTING. There is a certain danger which arises now and then out of the anxiety of photographers to secure absolute certainty of the value of the claims to permanency put forward on behalf of prints by various processes. There is a constant danger, in making the examination, of the misapplication or misuse of tests, which necessarily leads to erroneous conclusions. We should not, in testing for the purity of gold, reject it because we found it was not as hard as steel, or impeach the durability of a fabric because it was con- sumed when placed in the fire. Neither ought we, in test ing photographic prints, to submit them to inj urious agencies to which, in their ordinary preservation as works of art, they are not likely to be exposed, and the action of which they ought not to be expected to resist. All that should be expected of a photographic print, whether produced by silver printing or by some of the pig ment printing processes, is, that the image shall be produced in a manner and formed of materials not likely to change in the course of time, either from causes within itself, or from such exterior causes as a picture might be legitimately subjected to. If a photograph, when kept in a portfolio, or framed and glazed tor hanging on a wall, as an engraving would be. present as little change after the lapse of years as an engraving, it ought to be considered a permanent picture, and the result perfectly satisfactory. Destructive tests are, of course, out of the question. A photograph on glass may be broken; a print on paper may be torn or burnt; even an enamel may be crushed by a hammer, or melted in a sufficiently hot furnace; but these things do not affect permanency. Destructive tests, therefore, except where they anticipate by active means the probable gra dual action of ordinary and natural agencies, cannot be legitimately used, nor can conclusive arguments ever be derived from the issue. Again, in using legitimate tests, it is important, if honest conclusions are sought, that the legitimate examples of the process tested be employed. Carelessly or imperfectly treated prints by any process may fail when submitted to tests which are perfectly reasonable ; but the failure is, in such case, merely a proof of imperfect treatment, not of imperfect process. In short, it is only necessary here to say, that the experimentalist should carefully avoid the illogical process of generalizing from narrow or insufficient premises. We have been led to these remarks by a long letter re ceived some weeks ago from an old correspondent, stated to be for our “ careful consideration,” and for publication if we thought the matter ought to be discussed, and discussed now, so as to raise the issue ; “ Have the various new per manent printing processes made good their claims, or have they been tried and found wanting?” As our corre spondent’s arguments are plausibly' but moderately put, and probably represent a good deal of floating opinion, we shall make a full extract from his letter, and point out what we conceive to be fallacies in his positions. Passing over his introductory severe remarks, which we need not repeat, because they relate to persons with whom we can have no discussion, we commence with the practical part of his letter. He says:— “Dismissing photographic and literary quackery, however, has not the time come to raise the issue: Have the various new perma nent printing processes made good their claims, or have they been tried and found wanting ? Has their superiority over silver printing been so marked and undoubted as to justify photographers in aban doning, or even contemplating the abandonment of, a process which has been steadily improving for a quarter of a century, and has attained a high degree of perfection, for any of the carbon processes which remain yet to be tested, and which, if my own slight experi ence and common report may be trusted, are not so absolutely stead fast under severe tests after all ? And if this be so, where is the boasted certainty the new processes were to give us ? Uncertainty has been said to be the fatal stigma of silver prints on albuminized paper. I quote from memory the terms of one of your own articles on the advantages of carbon. ‘ The bane of silver printing is,’ you observed, 1 not so much the certainty that its results will fade, as the uncertainty that they will remain permanent.’ Has carbon, I ask, given us more'certainty ? And, if so, in which process ? “ If I do not bore you, I should like to give you the results of my own experience in making these examinations. I will begin with Swan’s process, ■which appears to have attained the highest degree of practical perfection, and may he said, I suppose, really to have entered the arena of commerce. I have heard something of Pro fessor Taylor examining some carbon prints submitted to him, one of which was destroyed by soaking, and the other uninjured. I do not know anything of the particulars, and cannot therefore offer this fact as an argument; but the story recalls my own experience. More than a couple of years ago, one of Swan’s prints came into my possession, which 11 wished to tint in water colours. I applied a wash of colour to the face, and before it was quite dry began to work a little more colour into parts. To my disgust the film began to ■work up, and the colour to take unevenly; and on further attempt to get a clean, even tint, blisters rose, and part of the film came away. On soaking the picture in water the film left the paper in shreds. I was told that the print had not been properly fixed ; but I knew that already, for I had proved it. But I think that I had proved something more; I had proved that carbon prints were not all permanent. “ Recently, whilst thinking of these things, it occurred to me to test some of Mr. Woodbury’s photo-relief prints, of which I had two or three specimens, which, I suppose, one may regard as carbon prints obtained mechanically. I had seen some discussion on them in the pages to which I have already alluded, but had not read it. I took the 1 Killarney Girl ’ given with the News, some few years ago, and sponged the print thoroughly. To my delight it stood perfectly. I therefore tried further, using a print which I had lately acquired. On applying a wet sponge, half the background was wiped out! Again 1 am told the picture was unfixed; and again I say I am only too well assured of the fact. But I presume that the picture was not intended to be unfixed; and therefore I repeat that the much desired certainty has not been found here. “ There is another point which I may as well mention in this con nection, as it weighs in my mind for something, and I know that it does so with many others. The two or three false starts in working this process commercially suggest the existence of practical difficulties. That at least two companies, who have heralded the process loudly, have come to grief before achieving anything, does not inspire con fidence. Swan’s process, as I said, seems fairly launched commer cially, but how is it so few people are practising the process ? Is it that the new company do not grant licenses, or that photographers are shy of obtaining them ? “ There is another carbon process—I mean Pouncy’s—which nobody seems to know much about. Four or five years ago you praised it highly, and I formed great hopes of it from what was then said. But how is it that it does not come before the public ? There is surely some hitch, or a process patented five years ago would have come into use before now. I cannot learn that a single photographer has done anything with it, either for business or amusement. Ono docs not see or hear of it at exhibitions; one does not hear of speci mens being shown at photographic meetings, where it is common to show novelties. I went to the Crystal Palace to see the specimens you noticed favourably some months ago, which had been removed from the Paris exhibition; but they only remained at Sydenham a short time, and were gone before I got there. The last specimen I saw was on talc, and the image was cracking off the talc. Perhaps
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