The photographic news

• Bandzählung: 29.1885
• Erscheinungsdatum: 1885
• Sprache: Englisch
• Signatur: F 135
• Vorlage: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: SLUB Dresden
• Rechtehinweis: Public Domain Mark 1.0
• URN: urn:nbn:de:bsz:14-db-id1780948042-188500006
• PURL: http://digital.slub-dresden.de/id1780948042-18850000
• OAI: oai:de:slub-dresden:db:id-1780948042-18850000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
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• Strukturtyp: Band

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• Strukturtyp: Ausgabe

412 THE PHOTOGRAPHIC NEWS. [JUNE 26, 1885. grain in the deepest parts is entirely lost, while it is visible in the covered lights. Soft, delicate negatives, not too intense in the lights and full of detail in the shadows, are the most suitable for the proces-. Hard negatives, which show great contrast and bare shadows, can be improved by coating the back of the plate with bichromated gelatine, and allowing the light to fall directly on this film through the negative. The exposures should not be carried too far, so that after washing there may remain only a light tint over the transparent parts. After exposure under the grained negative the print is inked and washed as usual, but a better effect is obtained by rolling in with a velvet roller, as described in Chap. VIII. After the transfer to stone or zinc, lights that are too full may be taken out with a scraper, and shadows that are too open may be filled in with a brush. Instead of laying the grained film between the negative and the sensitive paper, the operation may be performed as follows :—The varnished negative is coated with a solu tion of gelatine in glacial acetic acid and a little alcohol, and allowed to dry; the collodion copy of the grain original is lifted from the glass plate with paper, which should be rather smaller than the grained negative, so that the edges of the latter may be turned over upon it, and, without any thing further, is transferred upon the gelatinised negative. If required, the grain may, with a little care, be washed away again after use. Another way of using the grain original is to copy the grain on a glass plate and varnish it. This plate is used once for all until it is spoilt. The two negatives carrying the grain and the subject are put together, and a trans parency is taken in the camera. With a prolonged ex posure and a supplementary intensifying, it is changed into a suitable grain picture. If this transparency be taken on a bromide of silver emulsion plate, it can easily be changed into a negative by the process described in Chap. IV., or by constant copying in the usual way. The grained negative may also be obtained by taking a good silver print of the subject, and printing on it an impression of the required grain taken from stone, type, collotype, or copperplate, the impression of the grain being as strong as possible, and its opacity increased, if desired, by dusting with bronze powder. A copy is made in the usual way from this grained silver print. Sufficient ex posure and a supplementary intensification give the corresponding negative, which gives a very good result in skilled hands. We may remark that the specimens of photo-lithography in half-tone by Mariot’s process, published in the Con espondenz, are very perfect—i.e , they have all the qualities of a good lithograph, without the delicacy of the photographic detail being too much impaired. As Major Volkmer says, they will bear comparison with collotype, and the printing press stone has many advantages over the collotype plate, which is easily damaged, and often difficult to work. In his treatise on lleliographie,'Ptoi. Husnik has described various methods of producing grained negatives, among them one which he recommends as particularly suitable for photo-lithographic or photo-typographic purposes, and which is very similar to Mariot’s. For these purposes Prof. Husnik insists on the necessity of having a clear and well-defined grain, with its inter vening spaces perfectly clear and transparent on the nega tive. The only way of obtaining such plates is by dusting collotype plates with black lead. The collotype plates are prepared by taking 6 parts of the finest gelatine, and soaking it in 72 parts of water. When soft, it is dissolved with heat in a water bath, and then 1 part of bichromate of potash and 1 part of chloride of calcium are added, and the mixture is filtered. Glass plates that have been previously coated with the usual substratum, as for collotype printing, are coated with this mixture, the coating being double as thick as for collotype printing, so that the grain may be coarser. The plates are dried in a level position in a box, at a tem perature of 104° F. When the film is dry, it is exposed to light under the negative rather longer than is usual for collotype, and may be exposed in sunshine. The thicker the coating, the longer the exposure should be. Only in the very deepest shadows of the image should the plate be glassy and free from grain. The plate is then washed free from all bichromate, and covered, in a horizontal position, with a mixture of equal parts of glycerine and water. After a quarter of an hour, this is poured off, and the plate well wiped until all traces of glycerine are removed from the surface. It is then laid in a drying-box and warmed up to about 155% F. After half an hour the plate is dry, and all water removed from the glycerine absorbed within the film. The plate is then taken out and dusted with blacklead until it has the proper strength. In this way a grained negative is ob tained, in which the strength of the grain is dependent upon the thickness of the coating. After the dusting, the plate is laid face downwards in a mixture of 2 paits spirit and 1 part water, and left for half an hour or so to remove all glycerine. The plate is then taken out, dried, and varnished. Another method is to make a collotype plate, exactly in the same way as described above, but replacing the chlo ride of calcium by 1 part of sugar. The film must also be thick, but not so thick as to dry in waves, which cannot be got rid of afterwards. The exposure should be rather longer than with collo type plates with thiuner films, and is continued until the highest lights appear as shining points. After this the plate is washed, treated with glycerine, and inked. Such an inked plate may be used in two ways—either a transfer print may be made from it on paper coated with starch for transfer to zinc or stone; or a negative of the grained plate may be taken in the camera, which will show a very strong grain. If the inked plate is properly dried, and slightly dusted with plumbago to take off the stickiness of the printing ink, a grained positive is obtained, from which a negative may be made by contact printing on a dry plate. Dr. Schnauss has described another method, also in vented by Prof. Husnik, as follows :— A fine ground-glass plate is rubbed in with copper-plate printing ink, which is then cleaned off so that the ink re mains only in the depressions. The plate is then levelled and covered with a solution of gelatine (1 : 10) with the addition of 3 parts alcohol and gth glycerine. When this is dry, it is stripped, and will be found to have a very fine grain. It must be kept flat between the leaves of a book. The film is laid between the negative and the bichromated gelatine paper, and an exposure is given four times as long as in the ordinary process. Great care must be taken, in washing the ink off the print with a very fine sponge, not to injure the graining. The print should be allowed to soak rather longer than usually necessary, so that the ink may come away easily. The shadows may require a little extra pressure with a sponge cut to a point, but the lights should not be touched. Several methods of producing grained negatives have been patented within the last year or two, chiefly in con nection with the production of photo-blocks in half tones for letter-press printing. Most of them are modifications of previously known methods, and their object is, as a rule, to produce a lined or network grain, which is more suitable for type work than for printing from stone. We may therefore refer those interested in the matter to the speci fications of the patents. Many other ways of obtaining grained negatives suggest themselves ; for instance, there are many fabrics woven in black and white, in patterns quite suitable for giving a good mixed or regular grain. These can be copied and