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The photographic news
- Bandzählung
- 6.1862
- Erscheinungsdatum
- 1862
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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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- http://digital.slub-dresden.de/id1780948042-18620000
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- Seite 1-72 fehlen in der Vorlage. Vorlagebedingter Textverlust.
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- Bandzählung
- No. 220, November 21, 1862
- Digitalisat
- SLUB Dresden
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- Wahlperiode
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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
Band 6.1862
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562 THE PHOTOGRAPHIC NEWS. [November 21,1862. large buyer of photographs had regretted to him that many of his very fine specimens were gradually going: getting yellow, and showing less and less of the picture every time he looked at them. If this process of printing would give them prints which would not change, it would be a great boon, and they might even sacrifice a little brilliancy. The subject was clearly worth attention and experiment, and it would only be fair to Mr. Cooper that he should have some aid from other experi mentalists in bringing the process to perfection, in return for his pains and liberality in giving the results to photographers. For copies of engravings it appeared very excellent, as some of the specimens well showed, their tone being as rich, soft, and mellow as though they camo from the pencil of the artist. Mr. Cooper said that he had observed that resinized paper registered all the half tone in a negative much better than albumenized paper, and gave, consequently, softer and rounder prints. • The Secretary referred to the fact that albumenized prints did not necessarily fade. Some remained permanent, and this proved that fading was the result of imperfect or careless manipulation. After some further conversation on the subject, it was re marked that encaustic paste containing wax would gradually become yellow. To this it was replied that the quantity was so small as to be of slight importance in this respect, and Mr. Howard remarked that he had seen some of the exquisite tur pentine wax-paper negatives of the Rev. Lawson Sisson, which were free from any tinge of yellowness. A conversation followed on the discolouration of benzoin, in which Mr. Price observed that some paper prepared with it, sent to him by Mr. Cooper, had become more discoloured during the few weeks he had kept it. He intended to keep it twelve months as a test. Some further conversation on the import ance of very deep printing on resinized paper, and on its suit ability for colouring followed. Mr. Wall asked if Mr. Cooper had tried printing on canvas for painting in oil. Mr. Cooper had not tried prepared canvas, but the plain canvas would present no difficulty. After some further conversation, and a vote of thanks to Mr. Cooper, the proceedings terminated. Uorrespondente. COAGULATION OF DRIED ALBUMEN : A FALLACY OF PHOTOGRAPHERS. Dear Sib,—Taking the world in general, I think it must be concluded, that for every person who is able to detect a particular current fallacy, there are numbers who are un able to do so; and thus, error gets bandied about from one to another, till at last it comes to be considered as an accepted fact, even by those who should know better. Amongst the “ fallacies of photographers,” there is none more prevalent than the belief in the possibility of coagu lating dried albumen. I find Dr. Fowler disseminating this error, in his “ Short Lessons on Photography ” published in Humphrey’s Journal, and given at p. 415 of your present volume. Speaking of albumenized paper, he says,—“ It is certainly an advantage to coagulate the albumen on the dried surfaces, which prevents the solution of the albumen. This coagulation is best effected in the following manner:— The albumenized sheets are folded together in one roll, and then placed in a round tin box, much longer than the roll of paper ; the box is now dipped into a kettle of boiling water, deep enough for the water to stand higher on the outside than the top of the root on the inside. In this way the paper is submitted for some time to the heat of boiling water, which renders the albumen, in a measure, insoluble in the midia in which it has afterwards to be placed.” I likewise have read, as the suggestion of various other photo graphers, that the albumenized paper, should be ironed with a hot iron, in order “ to coagulate the albumen.” Now I unhesitatingly assert, that dried albumen, as exist ing on the surface of an albumenised sheet of paper, is not, and cannot be, coagulated by heat however applied; nor by sensitising it upon a nitrate of silver bath. The drier a substance be rendered, the longer the time required for its solution; and thus, the drier the state of the albumenized sheet of paper at the time of sensitising, the sooner the solu tion of nitrate of silver is enabled to render the albumen insoluble by its action upon it, and therefore, the less time has the water to ferment it sufficiently for solution: hence, the drier the paper, the less the discolouration of the bath. This insolubility, however, is not coagulation ; to produce the latter, fluidity is necessary. Albumen maybe said to exist in three states -.fluid, as in its normal state of white of egg; coagulated, as when the egg is boiled; and dried, as when the water it contains in ifs normal state, is evaporated at a lower temperature than that at which coagulation takes place. In each of these states, it has different properties. In both its normal and dried state, it is soluble in water, but not so, when it is coagulated ; at least, such is generally said to be the case, although a small portion of it is still so; in its normal state it can be coagulated by boiling water, heat, strong mineral acids, and metallic salts, and thus is rendered insoluble, except in a very slight degree; but, when once dried, it cannot in that state, be coaguluted. by any means ; it can, however, be still rendered nearly insoluble by strong mineral acids and metallic salts, but not by heat, however applied; and hence, from coagulation being accompanied by insolu bility, insolubility has erroneously been considered to be accompanied by coagulation. In short, strong mineral acids and metallic salts, cause in solubility and coagulation in its normal state, and in solubility without coagulation in its dried state. Fluidity being necessary for coagulation, dried albumen as such, cannot be coagulated by boiling water, heat, or any other means. The dissemination of any error, however innocuous it may appear, retards the advancement of knowledge, much more than most people are apt to imagine, for the honour then of science and truth, do not let us hear any more of the possi bility of coagulating dried albumen, unless indeed, what I state can be found to be false, and this I challenge any of your readers to do.—I remain, dear sir, yours truly, George Price. PRINTING DIFFICULTIES. Sir,—In the pursuit of hidden causes there is a fascinating influence exercised, that men care not to resist, for it is to this influence we are indebted for the many brilliant triumphs science has achieved. So long as visible results are the products of unseen causes our minds naturally remain unsatisfied, and the results are examined and re-examined with the most scrupulous care, and by a process of reasoning based on the information derived from our powers of obser vation, theories are propounded whose success depends on their stability whilst exposed to the fiery ordeal of scrutiny as they arc being analysed by a thousand penetratingly powerful intellects, which perhaps have long been labouring and searching in the same direction. In dealing with Mr. Eliot’s paper, we have results only to examine, for causes remain untouched ; that gentleman is therefore in error when fancying that he has launched into the photographic world a new “ theory,” but in common justice I feel bound to acknowledge his researches to be in the right direction, and like the friendly finger post, give us confidence as we endeavour to to push forward over the dark, and hitherto little trodden track we have chosen. An examination of the “ beakers ” will perhaps bear me out in this last statement, beaker No. 1 contains } grain soda to the grain of gold, but though submitted to the decomposing influence of hot water, the prints when exposed to the action of the solution when diluted, generate a bad colour and general mealiness, whilst 3 grains of the alkaline agent with 1 grain of gold under similar conditions yields tones which are satisfactory. Although I have not experimented in this direction, I am quite satisfied that Mr. Eliot is correct in his statement
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