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The photographic news
- Bandzählung
- 12.1868
- Erscheinungsdatum
- 1868
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- Englisch
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- F 135
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 501, April 9, 1868
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Zeitschrift
The photographic news
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Band
Band 12.1868
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- Titelblatt Titelblatt I
- Kapitel Preface III
- Ausgabe Ausgabe 1
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- Register The Index To Volume XII 619
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Band
Band 12.1868
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176 THE PHOTOGRAPHIC NEWS. [April 9, 1868. and clouds, in the middle distance we have a sheet of water, while the immediate foreground is made up of some dark objects, rooks, foliage, &c. If we expose a plate on this sub ject in the ordinary way, we shall probably find, on deve loping, that while the mountains and clouds in the distance are much over-exposed, the foreground has not been exposed sufficiently long to bring out any detail whatever beyond a general outline. There are two or three methods of reme dying this evil: one is effected by means of a flap shutter, which is fixed either inside the camera or in front of the lens. Bv these means the operator has sufficient control over his subject; whilst securing detail in the foreground, he does not sacrifice anything in the other parts of the picture, but all are harmoniously combined together. Much can also be done by the judicious application of the developer, keeping the same more on the foreground, whilst the development of distance, clouds, &c. are held in check ; then, again, in the printing, by skilfully masking the dif ferent parts of the"negative that would otherwise become too dark. Every landscape photographer should be in possession of a number of cloud negatives of different characters, so that he may always be able to introduce suitable skies in his pictures : they will be found very serviceable when printing from negatives which give white skies. Perhaps I shall have something to say on double-printing at some other time. I shall not attempt to lay down any rules for selecting, arranging, and composing the landscape ; but I would take this opportunity of recommending to all who take any interest in picture-making to read and study the excellent papers by Mr. H. P. Robinson, now being published in the PHOTOGRAPMIC News. And, in conclusion, let me impress upon the minds of all present, who have not made a know ledge of art their study, to lose no time in cultivating it; and let each and every member strive to encourage, assist, and stimulate each other, and may we all endeavour to pro duce something worthier and more creditable both to our selves, our art, and the Oldham Photographic Society. ON THE CAUSE OF DETERIORATION OF PRINTS MOUNTED ON CARDBOARD WITH GILT BOR DERS. BY MM. DAVANNE AND roRDos.* In December last we communicated to the Society a few remarks on the appearance of certain spots upon carte-de- visite photographs, a cause of deterioration which was seldom met with on pictures of a larger description. These spots were of the most minute kind, and always became visible, in greater or less numbers, a short time after the pictures had been mounted. The cause of this alteration in the photo graphs was due, we opined, to the presence of metallic powder in small quantities upon the surface of the card mount ; having now completed a series of careful investiga tions in reference to the subject, we are now able to state positively that such is the case. Our labours have been greatly facilitated by the kind assistance of our colleagues, who, readily responding to our call, have furnished us with information and subjects for examination. M. Dauvois procured for us samples of the different descriptions of powder used in gilding and orna menting card-mounts, and MM. Queval, Reutlinger, Cognac, and Jacoby, have forwarded examples of damaged pictures. The injury is due, as we have before stated, solely to the presence of minute particles of metal which become attached to and attack the picture; it being unnecessary that the metallic powder should be mixed with any sulphurous compound. M. Quval has furnished undisputed proof of this being the case by forwarding a few stereoscopic slides in which a perceptible line of these spots may be traced on the prints in those parts where a line of bronze is printed * Bead before the French Photographic Society. See also p. 124. underneath ; a microscopical examination of spots of a similar character on carte photographs showed them to be due to the same cause. If a little bronze powder is strewn over a piece of card board, even of the smoothest description, and then dusted off again, there remain in the pores of the cardboard small particles of bronze, which, although invisible to the naked eye, are very apparent with the aid of a microscope. A print mounted upon a card of this description soon becomes speckled, and the little spots, which appear white upon the surface, will be found to have a little black germ below, if the print is raised up by means of a needle point. The operations of mounting and rolling are often sufficient to remove a little of the powder from the bronze ornamental line round the picture; and these particles, becoming adherent to the surface of the print, likewise produce spots, but in this case the black germ will be found to be upper most, and becomes visible immediately. M. Jacoby forwarded to us carte pictures presenting the same obnoxious appearance, but mounted on cards not with gilt, but with red borders. We at first imagined that the ink used for these borders contained vermilion or sulphide of mercury, and that this was the cause of deterioration; the spots, however, were due, as in the other cases, to particles of metallic powder which must have become deposited on the prints during their sojourn in the atelier, or during their manipulation with the rolling-press (which had previously been used in finishing off pictures with gold borders); for an examination of the spots with the microscope betrayed the presence of minute particles of bronze not yet decom posed. A little dust collected in the atelier where the pictures were produced was found to contain a large quantity of these metallic particles. The largest and best proof remains to be mentioned : a small quantity of bronze powder was strewn over a picture, and its action was then closely watched in a damp atmo sphere. After a short time each metallic particle was found to have changed into a black speck, and to have become surrounded by a white halo presenting all the characteristic# of the spots which form the subject of the present examina tion. The explanation of the formation of these spots is very simple when we remember that the photographic image is composed, according to the researches of MM. Davanne and Girard, of metallic silver and an argento-organic compound, which forms the colouration of the picture. It is this argento-organic compound that is destroyed by the metallic particles, which exert a very rapid and intense action upon the print, especially when the latter has been insufficiently toned and washed. CARBON PRINTING. BY M. CAREY LEA. About a year since I made some experiments towards the simplification of carbon printing, which I left unfinished, with the intention of returning to them at a future day ; but I have not found the time, and M. Despaquis, in his experiments on mica printing, has hit upon an idea a good deal similar to that which I was working on. But my Pr! ciple was of much wider application than his, so that, believe, I may do some service in publishing it before so® 8 one takes out a patent for the idea. . It seems to me that if I could find a method of carbon print, ing in which the troublesome transfers could be done aWoY with, carbon printing would be considerably simpler thats silver printing, because of the absence of need of toning, pd could only be done by printing through the support. Itlas paper prepared in many ways (a method which Mr. Blair B long laboured at) without getting any satisfactory results, p r ' cipally, I think, because the bichromate solution penetra ers irregularly into the varnished or waxed paper, and rendat it unequally adiactinic. Glass presented the difficulty t
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