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The photographic news
- Bandzählung
- 27.1883
- Erscheinungsdatum
- 1883
- Sprache
- Englisch
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- F 135
- Vorlage
- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- Hochschule für Grafik und Buchkunst Leipzig
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- SLUB Dresden
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- Public Domain Mark 1.0
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- urn:nbn:de:bsz:14-db-id1780948042-188300004
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- http://digital.slub-dresden.de/id1780948042-18830000
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- oai:de:slub-dresden:db:id-1780948042-18830000
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- Bandzählung
- No. 1275, February 9, 1883
- Digitalisat
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Zeitschrift
The photographic news
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Band
Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
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Band
Band 27.1883
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- Titel
- The photographic news
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FEBRTARY 9, 1883.) THE PHOTOGRAPHIC NEWS. 91 of absorbing a sufficient quantity of water to render them tacky when damped in the usual way before transfer, and thus they adhere firmly to the stone in transferring. The stone may be passed through the press as often as may be necessary, without fear of double lines from the transfer slipping, and at the same time there is no difficulty in removing the paper from the stone when the transfer process is complete. The lines of the transfer are less likely to be ragged and broken than if the gelatine were removed from the paper, and further, the discarding of boiling or even warm water for washing the transfers is a great advantage. Finally, the ink, not being softened by hot or boiling water, is retained on the lines of the trans fer only according to the amount originally put on, and does not gather, and afterwards smash and thicken out on the stone. Mr. Deveril also says that in case of accident to the stone, or should a fresh transfer of a subject which has once been put down be needed, the once-used transfer print can be again inked, washed off, and transferred again. In cases where copies of subjects are likely to be wanted again, two or more prints are taken, the bichromate at once washed out; they are then dried and laid aside till required, when they can be inked, washed off, and trans ferred (see Photographic News, vol. xix., p. 585). Apart from the question of adherence to the stone, there is no doubt that photo-transfer papers prepared with an insoluble coating yield on the whole finer results than are usually obtained when the coating is washed away. We have therefore found it an advantage, especially for fine map work, to prepare paper in the usual way according to the Southampton method, and then allow the sensitive coating to become insoluble, either by keeping it for some days, or by exposing the back of it to the sun. When required for use, it is again coated with a mixture of gelatine and bichromate of half the usual strength, or sometimes even thinner, and when this is dry it may be exposed to light, inked, and washed in the usual way. In the hot weather it is found that the sensitized paper requires to be kept about three days before receiving the final sensitive coating. In the cold weather six days and upwards are required before the coating becomes suffi ciently hard. This time may, however, be shortened on emergency by laying the paper face downwards on a board, and allowing the light to act on the back surface for a minute or two. This may be done either after the print has been obtained from the negative, or just after the pre liminary coating has been given to the paper. The action of light set up by the sunning continues in the darkness, and thus hardens the film to the required extent in a very much shorter time than would be necessary in the dark alone. The addition of alum or chrome alum to the gelatine and bichromate solution used for the preliminary coatings will also harden the gelatine sufficiently to allow the paper to be used within two or three days in cold weather. It may be noticed that the bichromated paper should not be kept too long before being finally sensitized, otherwise the first coating becomes so hard and insoluble that the final coat ing does not adhere well to it, and the lines wash away. The advantage of this method is that abase of hardened gelatine remains on the paper, and retains the finest fines, while the fresh and easily soluble final coating preserves the clearness of the ground. It is necessary that the preliminary coating of gelatine should be thoroughly hardened, otherwise the transfers stick to the plate in transferring, and are difficult to remove without damaging the work. If soft, the gelatine is also liable to spread over the lines, and prevent their transfer ; on the other hand, as we have said, the coating must not be too hard. The proper point must be learnt by experience. Another advantage of this method is, that warm water is not required for the development of the prints, and the ink is not so liable to become pasty as in the usual way of working; The lines are found to keep crisp, and the spaces between them clear and free from greasy scum, thus giving much clearer and sharper transfer. This paper is also very suitable for the rolling-in methods. Sometimes it is more convenient to have a supply of simply gelatinized paper, which can be sensitized as required. For this purpose, bank post or Rive paper is coated with two coats of a six per cent, solution of gela tine. The single transfer paper prepared by the Autotype Company for pigment printing also answers admirably for photo-lithographic transfers. It is sensitized with a thin solution of bichromate and gelatine, the same as used for our own insoluble paper, and the after-treatment is the same, except that the washing-off method must be used, because the paper splits under the action of the roller. Mr. W. Paul sensitizes the same paper with a mixture of equal parts of albumen and saturated solution of bichro - mate of potash. After exposure, a coat of transfer ink is applied in the press, and the image is developed by wash ing, after soaking, in cold water. We have, however, obtained the best results with the Autotype Company’s special enamelled double transfer paper, which has a bright, glossy surface. For the wash ing method we sensitize the paper with thin gelatine and bichromate; but for rolling up it is sensitized with bichro mate only. It lends itself wonderfully well to the rolling- up method, and very perfect half-tone transfers may be obtained, though there are still the difficulties connected with grain and printing to be overcome. Captain Abney has patented a rolling-up transfer pro cess under the title of “ Papyrotype.” The paper for this method is prepared by coating any tough paper with a fine layer of gelatine, which is subsequently treated with chrome alum or alum. It then receives another coating of gelatine and bichromate prepared according to the South ampton formula, using the cheaper flake gelatine instead of fine cut. Professor Husnik, of Prague, prefers the use of gelatinized paper to which an additional coating of albu men has been given. According to the Professor, the undercoating of gelatine offers a firm resistance to the action of the sponge in developing the print, so that rubbing up of the paper and a deposit of fatty ink between its fibres cannot occur ; furthermore, the image is not easily damaged; the development proceeds of itself, exceedingly easily, since the coating of albumen softens, and is washed away from the paper along with the fatty ink. In this manner not only sharp pictures are obtained, but they are free from all half-tint. In his valuable work Das Gesammt Gebiet das Lichtdrucks, Professor Husnik gives a method in which fine letter paper is coated with a mixture of— Gelatine ... ... 4 parts Water ... ... 150 ,, Spirit of wine 20 ,, Glycerine ... ... ... ... 4 ,, The paper is wetted, laid on a level glass plate, and flowed over evenly with the above mixture. When dry, the paper can be kept till required for use. It is sensitized by floating for about two minutes on a filtered mixture of— Albumen (well-beaten and settled) ... 5 parts Distilled water ... ... ... ... 14 „ Bichromate of ammonia ... 1 part As it is rather inconvenient and expensive to prepare the albumen solution whenever required, and, perhaps, only for a small job, while neither the sensitized paper nor the solution will keep in good order for more than a day or two, Professor Husnik has prepared a paper ready coated with gelatine and albumen, which only requires sensitizing in a bath of bichromate. Such paper is obtainable in the foreign market, and gives, I find, very good results. Professor Husnik has not given the formula for its
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