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
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22 THE PHOTOGRAPHIC NEWS. [January 9, 1885. together, and produce various gradations of shade, while in the deepest shadows the particles of ink almost or quite run together and print quite black. If the drawing and printing are properly conducted, the result is a wonderful combination of softness of gradation and brilliancy of light and shade, though on close examination the breaking up produced by the grain of the stone is apparent through out. In another method the drawing is made with litho graphic crayon on paper specially prepared to show a grain, which may be varied in coarseness or character at pleasure. To be able, therefore, to print a photographic image on stone, it must be broken up in the same way into a collection of particles small, and separated in the lights, and becoming progressively closer and larger as the depth of shade increases. These particles must be clear and distinct, not so large as to destroy the fine photographic details, and at the same time not so small as to be liable to run together and print too dark. The general effect of the grain must be uniform, but it should not be dis agreeably prominent or monotonous in its regularity. Besides the mere mechanical difficulties of breaking up the delicate continuous gradation of the photograph into the broken grain of the crayon drawing, there are other considerations which tend to produce unsatisfactory results. In the first place, the lights and shades of even the best photographs from nature are not always all that can be desired from an artistic point of view, when translated into the heavy black and white of a lithograph. Even when a fair result has been ob tained from a suitable subject, the greatest skill and care are required to enable such delicate work to be printed in anything like large numbers. Not withstanding these defects, a really good method of photo lithography in half-tone would have many advantages over other photo-mechanical processes in quickness, cheapness, and certainty ; the subject, therefore, is well worthy of atten tion. With these preliminary remarks, we may proceed to con sider the various methods by which it has been proposed to attain this object. They may bo classified under four general heads, as follows :— 1st. Those in which the photographic image itself is grained on the stone. 2nd. Those in which no special arrangement is made for graining. 3rd. Those in which a screen, or medium bearing a grain, is interposed between the negative and the sensitive surface, whether on stone, metal, or paper. The grain may be a network, like fine wire-gauze, crape, muslin, lace, net, or other tissues, or photographic impressions of the same, enlarged or reduced. Or it may be an impression from a plate engraved with a net-work formed of dots or cross lines; or a stipple of dots or points of various sizes, as in a crayon or aquatint grain. This impression may be printed on a thin, transparent medium, such as collodion or gela tine, or it may be transferred or printed on to the sensitive surface before the negative is placed in contact with it, or on to the surface of the negative itself. The negative or sensitive surface may be brushed or dusted over with some granular powder, which will form a fine grain, without interfering too much with the action of light. 4th. These methods, in which advantage is taken of the natural vermicular wrinkling or reticulation that is formed on gelatine printing surfaces, such as are used in photo collotype printing, and can be increased or diminished at will, according to the thickness of the film and the tempera ture at which it is dried. This grain almost disappears in the deep shadows, but becomes progressively coarser and more strongly marked from the shadows to the lights, and, as we have seen before, this is just what is wanted. All that is necessary is to prepare a collotype printing film giving the requisite grain ; to print the subject on this film, from a reversed negative ; then to carefully pull a print from it for transfer to stone or zinc. Having made the transfer, a skilful draughtsman can easily open up lights and deepen shadows. Lettering, &c., may be added, and the subject printed at once from the stone. The ink-photo process, now being so successfully worked by Messis. Sprague and Company, of which many admirable examples have been given as supplement to the News, is apparently of this kind. The only objection to it is that the grain may be come unduly prominent, and destroy fine detail, though the general effect is good. As we shall see further on, the collotype gtain may also be applied, and perhaps with better results, in the manner of the processes categorised under the 3rd class. I. The first method, in which the image on the stone is grained, is chiefly applicable to the asphaltum processes. In chapter xv. we have already seen that Messrs. Barreswil and Davanne obtained grain by dissolving asphaltum in ether, and were able to produce satisfactory prints in half tones. A more certain method is that described by L- Schrank, in the Correspond'.nz for 1871 (News, vol. xv. p. 368) in which the grain is produced by developing an asphaltum image on a grained stone, and then carefully opening the film of asphaltum by rubbing it with moist sand, pumice-stone, or cuttle-fish powder, so as to lay bare the grain of the stone. In the shadows, where the layer of asphalt is comparatively thick, few points of the grained surface will break through ; but in the thinner portions of the imago more points of the surface will be laid bare in proportion to the thinness of the film. When the image is considered sufficiently grained it is etched, by which the gum and acid penetrate into the little spaces which have been opened out, and prevent the iuk taking on them. A grained image is thus produced similar to a chalk drawing. The writer has seen some very satisfactory results produced in this manner, some years ago, by Messrs. Reiffenstein and Roesch, of Vienna. At the Paris Exhibition of 18G8, some very fine photo lithographs, in half-tones, were exhibited by M. Marie, of Paris. His exact way of working is not known, but it seems likely that it was based on the use of grained asphaltum images. The peculiarity of his process was that the results were obtained by separate printings for the shadows, middle tints, and lighter tints. The results were very effective, and practically, perhaps, the best half-tone photo-lithographs that have ever been produced. Good results in half-tone, by transfer on stone, are said to have been obtained by Mr. Pouncy’s process. He de veloped the bitumen image on paper coated with gum, transferred it to a grained stone, and then grained it. Grained images in bitumen could, however, easily be obtained by printing under the grained negatives, to be described further on. They might be either direct on the stone or zinc, or transferred from a paper or tissue, pre pared in the way suggested by M. Despaquis (chap. xv). The latter mode of working, if feasible, would appear to have some advantages over the collochromate methods in sharpness and delicacy of detail. II. Under the second heading we may include those collochromate processes in which no special arrangement is made forgiving a grain to the image, or it is produced simply by the roughness of the transfer paper and the abrasion of the sponge in washing. The simplest of these methods is Poitevin’s, already described in chapter xii. The image being entirely on the colloid surface, the process is more nearly allied to collo type than to photo-lithography proper. The images are easily worn out, and do not yield long impressions. (To be continued.) DIARY OF A DEBUTANT.* September 27th.—Forgot to put diaphragm in. Then took two of doctor and chief officer; but, on going to develop, found there were no plates in the holder. Took two more of same, and * Photographic Times,