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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. 516, July 24, 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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358 THE PHOTOGRAPHIC NEWS. [JULY 24, 1868. If the cause of fogging has thus been satisfactorily traced and cured, it will form an excellent lesson. But as there are other causes of fogging than an imperfect yellow window, let us examine Case B. Case B, the plate darkens all over under the action of the developer, and you can distinguish no difference b .tween the two halves ; this shows that your window is quite right, and you must seek further for the cause. It must now lie between the bath, the collodion, and the developer. First try the bath : test it with a strip of reddened litmus paper, and if it changes to blue the bath is alkaline, and an alka line bath is a certain cause of fogging. Add acetic acid, drop by drop, testing between each addition, until blue litmus paper is very slightly reddened. Again try a plate; the fogging will probably not be quite gone, but much re duced : add a little more acid until it entirely disappears. Suppose, however, that the reddened litmus p iper did not change colour, then test with bine litmus, and if it turn very red, carefully neutralize with oxide of silver or ammonia, until only a slight acidity remains ; then resume your trial to see if you have expelled your enemy, for excess of acid, especially nitric, will cause fog. Should the test papers show that the bath is neither very acid nor alkaline, the probability is that the error is in the developer or the collodion. Make up, carefully, a fresh developing solution, being par- ticular not to omit the full proportion of acetic acid. You may even increase the quantity of acid, for some samples are weak, and you may happen to have one; the developing solution, unless it have its proper addition of acid, will always cause fog. If the new developing solution rid you of your difficulty, well and good ; if not, you must suspect your collodion. Some collodions cause fog; therefore, get some fresh, and let it have a little colour—a pale golden, lor instance —for colourless collodions are more prone to fog than coloured ones. If you are not now relieved, you may assune that the nitrate bath is the defaulter, for it must bo one of the three. Make up a new bath, and if you use good silver and clean water you are almost certain to be out of your trouble. In this way, by carefully and exhaustively examining one thing at a time, you will be certain to trace out the delin quent material. If you have decided that the nitrate bath, for instance, is the cause, then you have, if it be a new one, to find out whether the sample of nitrate of silver is pure, or whether the water is not the cause. The latter is frequently an unsuspected source of trouble. Again, if it be found that the developer is at fault, supposing it to be correctly mixed, each of its components may be suspected and examined in turn—the iron, the water, the acetic acid, and the alcohol. Some samples of methylated alcohol often cause great annoy ance by impurity. To return to our examination : supposing that we have not yet discovered the cause of our fog; the conditions of Cases A or B not applying, let us examine the rest. Case C, the plate develops perfectly clean and transparent all over ; this shows not only that the yellow window is all right, but that the chemicals are right also; in fact, that the origin of the fog must be external to the dark room ; and as nothing else but diffused light can now be the cause, we must seek to discover it. First examine the dark slide well; ip some unsuspected manner it may admit light to the plate. If your dark slide be found to be perfect, next examine your camera carefully. You may test it in this manner : pre pare a sensitive plate as usual, and place it in the camera as if you were going to take a picture; put the cap on the. lens, draw up, half way only, the shutter ot the dark slide, but do not uncover the lens. Let the plate remain thus for a full minute, then develop and fix the plate. The plate will either be one-half fogged, or it will be quite clear all over. If half be fogged, it shows that the camera admits light in some other manner than th rough the lens, and thus the fog is caused. To know where the light is admitted, remove the ground glass ; and, excluding all light with the focussing-cloth, put your head into the camera (the lens being still covered), and yon will see the light streaming in. You may examine the interior of your camera in another manner. Place the dark slide in its place, and draw up the shutter ; remove the lens, and, with the aid of the focussing-cloth again, examine the interior through the flange aperture. If any stray light be admitted, you will see it reflected from the face of the plate. It is necessary, when thus examining the interior of a camera, to wait for a few minutes, to allow the eye to get accustomed to the darkness, or you may deceive yourself, and think there is no light, from your momentary inability to perceive ’it. The cracks, crevices, or holes being stopped up, your trouble is passed. Should your plate, however, develop clear all over, it will show that the interior of the camera is perfect. Another cause of fog mayarise from the lens itself. If a stronglight fall on it, particularly sunshine, fog will certainly be pro duced. A screen or shade should be provided, so that no light fall on the lens, except from the objects that are being delineated. Occasionally there is reflection from the sides of the lens tube, or the edges of the back lens. Dead-black varnish will be the remedy in these cases. If you have not now traced out the difficulty, having run through your chemicals and apparatus, it most probably is caused by an error of manipulation, such as over-exposure, or a deviation from the proper mode of developing. It is scarcely probable, however, that you could pursue this in quiry without already having a clue to the real cause ; and I have gone through the series of exhaustive experiments to show you that, by this method of inquiry, you may succeed in tracing not only fog, but almost any other trouble, to its true source. Corresponence. INFORMERS AND PIRACY.—GRAVES v. MERCER. Sir,—We should much prefer to have remained silent as to your introductory remarks in the case of “ Graves v. Mercer,” reported in your number of the 10th inst, had not “ The De fendant ” of his own accord rushed into print. We forbear to remark upon any of the numerous inaccuracies in the letter signed “ The Defendant,” unless under the advice of our soli citorin the case, which would necessarily involve so much delay in our replying as to lead your readers to suppose that we accept “ The Defendant’s ” assertions as unanswerable. Wo may perhaps venture to encroach upon your space at some future time, but meanwhile we would remind “ The Defend ant ” of the old proverb, “ Don’t holloa till you’re out of the woods.” Others quite as confident and as plausible as “ The Defendant” have, nevertheless, eventually como to griof. As regards the employment of so-called informers, we, more than any, do regret that the law should be so ineffective as to leave us no other alternative, in the face of the many dodges adopted by dealers and others engaged in this illegal traffic, than the use of such means, in order, in some measure, to de fend ourselves from the acts of persons not over-scrupulous as to the proper constructions of “ meum ” and “ tuuin.” Had you had the experience that we have had of the diffi culty in tracing out these matters, in order to suppress a traffic ruinous to ourselves, but doubly serious as it affects the fine arts in this country, we cannot but think you would readily endorse the opinion expressed from the Bench by one of our ablest London magistrates, that “ we are justified in adopting any means short of felony ” in such cases. W e have selected as we consider respectable men, who are under our own control, and we see no reason to question either their truthfulness or their sobriety. We trust sincerely that the law in this respect will ere long bo amended, so that the necessity of proving a sale will be done away with, and some other more simple, speedy, and effective remedy provided.—Wo are, your most obedient servants, Henry Graves and Co. 6, Pall Mall, July 22nd, 18G8.
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