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The photographic news
- Bandzählung
- 6.1862
- Erscheinungsdatum
- 1862
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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. 196, June 6, 1862
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Zeitschrift
The photographic news
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Band 6.1862
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- Register Index 619
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Band 6.1862
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[June 6, 1862. THE INFLUENCE OF BROMIDES IN COLLODION. BY ALFRED KEENE. The experiments both of Mr. Sutton and Mr. Blanchard, given in the News of the 16th ult., for elucidating this subject, appear to me open to objections; those by the former gentleman, as you correctly observe, from being per formed with a collodion containing a bromide only, instead of the combined salts—iodide and bromide; also, probably from Mr. Sutton being so strong an advocate for excess of alcohol; the normal collodion he used was of that character, and if so it may account, not only for the length of time he has found necessary for the decomposition of the bromide in the collodion, and its conversion into bromide of silver, but also in some measure for other opposite peculiarities in his experience. Paradoxical as it may appear, collodion containing a large excess of alcohol is less quickly acted upon by the bath than one containing excess, or equal por tions of ether, which may be explained by the fact that alcohol, though having great affinity for water, makes a film of a very homogeneous nature, that sets more like albumen or gelatine, and therefore offers little facility for the bath to penetrate, and produce the chemical change. Ether, on the other hand, though possessing little affinity for water, gives more porosity to the film, which allows the bath to pene trate freely, and come in contact with a very much larger quantity of the bromide, and consequently quickly decom pose it. Again, during investigations on the character of alcoholic collodion, I have noticed that the excess of alcohol modifies it in some respect similar to what a bromide docs ordinary iodized collodion, for instance, a collodion simply iodized, made with three or four parts of alcohol to one of ether, will bear a stronger iron developer, and also its being kept on longer without producing fog or stain, than one made with three to fee, or equal parts of ether. If, therefore, Mr. Sutton has used an alcoholic collodion, and those who differ from him the, I think, far preferable kind, made with say equal portions of ether, some of their opposite results may be thus explained. Mr. Blanchard’s experiments appear at first sight satis factory, and to promise definite results, simply iodized and bromo-iodized collodions being compared with the use of the same bath, same developers, and exposure for each respective set; but the very care devoted to insure unifor mity of treatment has defeated his object. All who have experimented largely will have observed that not only must the bath, developer, and collodion bear certain relative pro portions—a strong bath or strong developer fogs a weak collodion, i. e., one containing a small comparative quantity of iodide—but also that bromides enable a collodion to bear, and, I may say, cause it to require, a stronger developer, and of its being kept on longer than a simply iodized collodion, the latter fogging all over almost immediately, under the action of a developer suitable for the former, which will account for all the simply iodized collodion plates treated in Mr. Blanchard’s experiments fogging, and the bromo-iodized remaining clear and clean, without deciding the respective merits of each. The developer used chiefly being a 30-grain iron one, and the iodized collodion only of the strength of from 3} to 4} grains, according to the salt used per ounce, for which a 10 or 15 grain developer would have been more suited ; whereas the bromo-iodizer contained from one grain of bromide upwards in addition, and in some instances also extra iodide. To arrive at correct conclusions respecting their comparative sensitiveness, we must prepare and rise the collodions under circumstances best adapted for each. As regards the respective merits of iodized and bromo- iodized collodions, nothing, I think, can be more conclusive in favour of the latter, than the universal preference shown for it when the two salts are judiciously combined with a suitable pyroxylinc, in proportions that bring out fully the peculiar advantages of each; but on the other hand there arc undoubtedly circumstances, even though they may be rare, under which the former gives the best results. I think therefore, it cannot be advisable exclusively to advance« condemn either, which is taking too narrow a view of th subject, but consider it desirable instead to ascertain whid is best adapted for general use; whether either possesses peculiar characteristics, or offers peculiar advantages undet particular circumstances over the other, and if so, what! Having devoted, during the early part of the year, consi derable time and attention to the subject, I submit a sun mary of the conclusions arrived at as the result of them The separate results, amounting to probably several hun dreds, were very varied, as might be expected when I explain that collodions made with almost every variety of pyroxy line, and prepared with ether and alcohol, ranging in pn portions of from five to three to one to five, and containing iodides and bromides in various proportions and quantities, and iodides of various quantities were used; also developed weak and strong, and light varying from the dullest to mos brilliant. Iodized collodion, characteristics—Simply iodized collodion when developers of suitable strength were used, as compare with bromo-iodized with the same developers, proved rathd more sensitive, developed in less than half the time, and i very dull weather or a badly-lighted room—with light well diffused—when but little contrast of light and shade, more brilliant picture—picture with better contrast, bul will not bear a developer half the strength, or continued o’ half the time without fogging ; is more liable to stains an marks, more quickly solarizes, and very liable to be deficient in half tone, excepting under the circumstances mentioned as favourable for it. Bromo-iodized collodion, as compared with simply iodized requires rather longer exposure when a developer suitabll for the latter is used, but as short or even shorter exposu" when a strong developer is employed, works cleaner, is n0 liable to solarize, gives more half tone, softer and mo pleasing results, particularly when the light is brillianl decidedly preferable for general use, and may be considertt essential for cartes de visite and view purposes. The ordina bromo-iodized collodion, containing a small portion 0 bromide, which works quick, clean, and brilliant, I f0 most suited for all ordinary requirements, but there arc c |! cumstances, more especially in view photography, and * times for portraiture, where there arc extreme contrasts colour, or light and shade, or any other cause, render10 the use of a very strong developer, and comparative IC’ continued action of it desirable, without producing fog 0 loss of definition in the high lights, when a collodion C® taining as much as equivalent proportions of each St. answers best, or a mixture of it with the weaker bron iodized. The larger the quantity of bromide, the strong may be the developer. I have used with a collodion, taining equivalents of each salt, as much as 80 grains iron, and 15 minims glacial acetic acid to the ounce, very good effect, without producing fog, and the neg 8 ® requiring little after intensifying with pyro and silver. ON THE EFFCTS OF AFFINITY IN PHOTO GRAPHY. BY DB. SCHNAUSS.* If gold be separated from its solution by silver, the 1 8 ^ enters into the combination in place of the gold, and, ASd photography gold is employed under the form of chlol of gold, or hyposulphite of gold, it is evident that i ' j. form analogous combinations of chloride, and of hyPOb phite of silver. It is identical with the chemical procesie which the Tree of Diana is produced, by immersing a er of zinc in a solution of acetate of lead. The lead, 8 c j feeble electro-positive metal, is precipitated upon the 1P the form of a delicate moss. * Continued from p. 20.
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