The photographic news

• Bandzählung: 11.1867
• Erscheinungsdatum: 1867
• Sprache: Englisch
• Signatur: F 135
• Vorlage: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: Hochschule für Grafik und Buchkunst Leipzig
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• Sammlungen: Fotografie
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THE PHOTOGRAPHIC NEWS. Vol. XI. No. 474.—Octoler 4, 1857. CONTENTS. PAGE Matt Silver Stains on the Negative 473 Photography and the Abyssinian Expedition 475 Critical Notices 476 Echoes of the Month. By an Old Photographer 476 Nicephore Niepce and the Origin of Photography 478 MATT SILVER STAINS ON THE NEGATIVE. Tub summer season generally brings with it, as well as many advantages, the recurrence of certain troubles to the photographer, not the least of which is the prevalence of silver stains on the negative, varying slightly in form, but of one generic character, and known as matt silver stains, oyster-shell markings, slug tracks, marblings, &c. The origin and cure of these troubles has been the subject of much discussion, and various causes, probable or occult, have been suggested as producing the defect. During the present summer we have received from correspondents fewer complaints than usual of the advent of this evil, and two or three of our readers who have been troubled with it have written to say that suggestions we had made, to which we shall again refer, had enabled them to get rid of the defect. Our attention has recently been called to another, and to us novel, form of this defect. The matt silver stains were present, but in a newform. Unlike slug tracks, oyster shells, or marbled markings, these stains were of a plumose form, giving exceedingly delicate and well-defined feather-like markings, each of which was from one to two inches long. They always occurred at one end of the plate—that at which the collodion was poured off, and was therefore the least set when the plate was immersed in the bath—and, as this was the end which was uppermost in the bath and in the dark slide, the end from which the silver solution was most per fectly drained. The general effect of the markings was that of very pretty plumose crystallization, extending two or three inches into a 10 by 8 plate. Like most matt silver stains, the markings might be removed by means of a camel’s- hair pencil or a little cotton-wool, but, when removed, the image underneath was generally also rubbed off wholly, or partially. 'The weather was not particularly hot when these stains were produced, nor were the plates kept very long between removing from the bath and development. The same materials had a few days previously worked well in all respects, and, with the exception of these markings, the negatives were excellent. An old sample of collodion and a new one by the same maker, and an old sample by another maker, all gave similar results in the same bath, suggesting that the latter was the source of the evil. We have described this example of the evil in question somewhat minutely, because it is novel in form, and appears under somewhat novel circumstances, and we should be glad to know if any of our readers have met with similar experi ences. At present we cannot suggest any special cause for this special form of a common evil. On the general sub ject and some of the successful remedies we have one or two remarks to make. We shall first quote for comment some ob servations in the Philadelphia Photographer by Mr. Carey Lea, who has devoted considerable attention to these stains, which, in his observations, assume various forms, such as rias Photographs as Mural Decorations 479 “ The Times " on Photography at the Paris Exhibition 479 Photographic Residues. By Prof. Towler 482 Talk in the Studio 483 To Correspondents 484 roundish blots, concentric circles, crescents, arabesques, and long smears. They possess, he says, the following character istics:— 1. They are light-grey white and silvery, but have not a full metallic lustre. 2. They are not in the film, hut on it. 3. They appear almost exclusively in warm weather—at least, are much more troublesome in such. 4. They appear indifferently with an iron or pyrogallic de velopment. 5. They are most apt to show themselves when some little time elapses between sensitizing and development, often accom panying otherwise faultless plates. After referring to some of the various opinions which have been expressed on this subject, and stating that he has only lately had much trouble with these markings, Mr. Lea pro ceeds to say:— I believe, however, that by a careful study of this matter I have been able to arrive at the cause of the trouble. The great source of these stains I hold to be letting the film become too dry before plunging it into the nitrate bath. It will easily be seen, then, why these stains occur princi pally in summer, because then the drying is so much more rapid, and due allowance is not made for it. I conclude from my results that in hot dry weather there is scarcely more than time enough to get a plate into the bath after pouring off the excess of collodion. Of course the plate requires to be rocked until the drops just cease to fall, then it should bo laid quickly on the dipper and be plunged in—not, however, suddenly or rapidly. The same amount of drying that in damp cold weather may require half a minute or more after the rocking is done will take place in hot dry weather whilst the liquid is being drained into the pouring-off bottle. A plate is never too soon in the bath unless the film exhibits injury in consequence. Some say that when the interval is too short the film will leave the plate in ribbons. This I have never seen take place except with very bad pyroxyline. Ac cording to my experience, when a plate has not had the need ful time, that fact makes itself evident by a peculiar change in the structure of the film, most apt to appear in a roundish spot a couple of inches (more or less) in diameter, generally showing itself towards the middle of the plate. The appearance of this spot it is not very easy to describe ; perhaps I may give some idea of it by saying that it recalls the inside structure of a freshly-broken lump of camphor. Moreover, this appearance must be known to most photographers. So long as this is avoided, the Jess time, I am satisfied, that intervenes between the pouring on of the collodion and its immersion in the bath the better. I hold, then, that the tendency to these stains may, to a great extent, be got over by reducing the interval between collodionizing the glass and plunging it into the bath as much as possible. Amongst other things, the chief practical effect of the rapid immersion of the plate in the bath before the col lodion is too much set is to cause it the more readily and the