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The photographic news
- Bandzählung
- 27.1883
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- 1883
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- Englisch
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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. 1277, February 23, 1883
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The photographic news
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- Titelblatt Titelblatt I
- Register Index III
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119 by three feet wide ; the method I use in lifting them is to pass a wooden roller under the side of the print, then gently raise the roller, holding the print with the hands to prevent it slipping off, then it can easily be placed over the wooden bar covered with sheets of blotting-paper to dry. Those who prefer pre paring their own paper can easily do so, the only points to be attended to being the selection of a suita’ • paper and the mixing of the salts. I have found a hardish « aglazed paper to answer best; after being sensitized, it must be dried in a warm dark room, and then kept from the light until required for use. The chemicals used for sensitizing are: potassium, ferri cyanide, and ammonio-citrate of iron. Separately, these salts are not affected by light, but when they are mixed, a new com pound is formed, which, upon being exposed to sunlight, is decomposed with the formation of prussian blue, which, after being washed, gives the paper the beautiful bluish tint. The exact chemical reactions are undoubtedly complex, and I refrain from entering into them. The proportions I have found to give the best results are: one part of ammonio-citrate of iron to five parts of water, and one part of ferri-cyanide of potassium to four parts of water, mixed together in equal quantities. The paper may be coated with this solution with a large camel’s hair brush, one even coat being sufficient; the paper being dried, is then ready for use. This system of blue printing can be still further extended by the aid of photography, and may be employed to print copies from glass negatives of machinery, models, &c., at a very low cost, and without skilled assistance. PELLET’S PATENT DIRECT COPYING PROCESS. BY EDGAR GOOLD.* The mechanical part of this process can be described in very few words, although it is much more complicated than Marion’s process, inasmuch as the prints have to be developed in two solutions, viz., the yellow prussiate of potash bath, and the hydrochloric acid baths respectively; after being in each of these baths, the prints must be well washed in clean water. The method of finishing prints by this process occupies much more time and care than the one I have just illustrated ; while its great advantage is the extreme sensitiveness of the paper and the consequent shorter exposure in the printing frame. The exposure can only be determined by constant practice and test slips, the exposure varying from half a minute upwards according to the intensity of the light. Testing the exposure with the test slips before mentioned is best done by placing three or four of these slips under a piece of paper, of the same quality as the original tracing, with a few lines marked on it, and exposing in a smaller frame placed along side on the tracing being copied. After the print has been subjected to the action of light for a short time, draw out one slip, dip it in the prussiate solution, and watch the chemical action for about three-quarters of a minute ; if the background remains yellow and the lines come out blue, the exposure has been suffi cient ; if, however, the background comes out with a bluish tinge, the frame must be re-exposed. Whilst testing, the frame must be covered or turned face downwards. It is absolutely necessary that test slips be taken from the same roll of paper as the one used for the copy. The print must be made so as to form a sort of tray about three-quarters of an inch in depth, by carefully turning up the edges with the aid of a straight edge. The print must then be floated face downwards in a saturated solution of yellow prussiate of potash previously mixed with hot water and allowed to cool After floating the copy in the prussiate bath for half a minute, raise the print at one end with great care ; this ought to be done without allowing any of the prussiate solution to get on the back of the print, as this would cause stains. It must now be held up, and the chemical action allowed to continue until faint blue spots begin to appear in the background; it must then be immediately immersed face downwards in a trough of clean water, to check the further action of the prus siate solution ; one edge of the paper must now be depressed under the surface of the water, then lift the whole paper by that edge to allow the water to flow all over the back of it. After repeating this washing two or three times, the print must be placed in the hydrochloric acid bath (strength, one part of acid to ten of water), and wholly immersed for from five to fifteen minutes, the surface being worked all over with a brush to start and loosen the blue mucilage. The copy is next taken out of the acid bath, and placed in a tray containing clean water, where it must again be well rubbed all over with a brush to clear it of the superficial gum mucilage ; after washing, the lines of your print will be found to stand out blue on a white ground. A ny blue stains on the copies may be removed by the use of the “ blue solving liquid ” applied very lightly with a camel’s hair brush to the part to be erased, and when dried with blotting- paper, the stains will entirely disappear. This solving solution is supplied with the paper. Zotes. Dr. Liesegang has this year issued a little annual under the name of Photographischer Almanack. This is German Annual No. 3. Dr. Hornig’s valuable Jahrkuchiot 1883 also comes to us from Vienna ; it is in pocket-diary form, and contains much that is useful, and nought that is useless. The Philadelphia Photographer has this month, by way'of frontispiece, a collection of bijou sketches from “ Merrie England,” being reductions from the well-known studies of Mr. H. P. Robinson, of Tunbridge Wells. Conspicuous among the sylvan pictures is the wonderful “ Merry Tale,” one of Mr. Robinson’s latest triumphs. The first number of the St. Louis Photographer has also reached us, our friendly rival from St. Louis, under a new name. Mr. J. M. Tomlinson announces himself as editor. Mr. C. Ray Woods sailed for Panama, on his way to the Pacific, on Saturday. lie hopes to arrive at his destination, Caroline Island, about the middle of April: the long eclipse, our readers will remember, happens on May 6th. A question of some importance is involved in the lighting of dark-rooms, apart from the chemical effect of light upon the photographic plate. It is a somewhat serious fact that since the introduction of gelatine plates many photographers complain of their sight not being so good as formerly. W hether this be due to the small quantity of light which the rapid plates of the present day demand, and the conse quent straining of the eyesight in watching the development, we cannot absolutely say; but it is certainly possible. Talking with two photographers of eminence after the dis cussion at the last meeting of the Photographic Society, both agreed that their sight of late years had suffered. In one case the defect was as singular as it was disquieting. It appeared to be a species of colour blindness, but developed in a most unusual manner. Thus, on looking at one of the pictures on the wall of the room, there seemed to be a patch totally devoid of colour, as though the portion of the retina on which this patch was depicted had lost its sensitiveness. If this failing of eyesight be confirmed by other dry plate workers, it is evident that no time should be lost in satis factorily settling the effectual lighting of dark-rooms. It
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