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THE PHOTOGRAPHIC NEWS, Vol. XXVII. No. 1298.—July 20, 1883. CONTENTS. Prints on Salted Paper 449 Some of the Uses of Common Alum 449 Carbon Pictures for Crystoleum Painting. By W. T. Wilkinson 450 French Correspondence. By Leon Vidal 450 The Translation of Colour into Monochrome by Photographic Means. By J. R. Sawyer 451 The Effect of Shearing Stress on Sensitive Salts. By Captain Abney, 452 Gun-cotton and Pyroxyline: The Question of Permanence. By John Spiller, F.C.S 453 A New Unit of Light in Connection with Sensitometry. By James B. Spurge 453 PAGE Melhuish’s Roller Slide 455 Notes 43) Patent Intelli gen ce 458 Lessons in Optics for Photographers. By Capt. Abney i A Dictionary of Photography :p-: 46, The Exhibition of the Photographic Society of Great Britain... 461 Correspondence 1, Proceedings of Societies 76; Talk in the Studio 463 To Correspondents 16 Photographs Registered •* 467 The Every-Day Formulary I. 404 PRINTS ON SALTED PAPER. It is strange to note how universal is the adoption of the albumen process as a method of positive printing ; and so far is this mode of producing positive photographs become universal, that the first point to be considered in connec tion with any new printing process is, how far the results resemble, or can be made to resemble, pictures on albu- menized paper. The albumen process of printing has made its way under what might be regarded as very considerable dis advantages, as the results are notoriously liable to rapid fading; they are by no means well adapted to receive the work of the colourist or of the retoucher, and possess a gloss which many regard as highly inartistic and vulgar. Ordinary collodion negatives or positives, as well as prints—in the production of which the dangerous sulphur- containing albumen takes no part—are well known to be, under ordinary circumstances, far more permanent than pictures on albumenized paper ; and it would probably be well worth while for the photographic profession to make an effort to educate the public to a just appreciation of the results which can be obtained on plain salted paper. One notable advantage of this course would be the great facility with which high-class artistic work can be brought to bear on the results. A preliminary trial, which will abundantly serve to give a notion as to the kind of pictures which can be obtained on salted paper, may be made with the ordinary albu menized paper, the back being sensitized instead of the front. But this course is not to be recommended as a general proceeding, as there may be some risk of sulphur from the albumen coating affecting the image; and it is by no means an economical expedient to replace salted paper by albumenized paper. W hen the back of the albumenized paper is sensitized and printed upon, very little difference will be noticed as regards the details of the subsequent operations ; but the print will generally be reduced more than usual during fixation, and it will ordinarily be found to tone more rapidly. For printing on plain paper, either Saxe or Rive’s may be used ; but we are rather inclined to prefer the latter. The salting bath consists merely of a solution of one part of ammonium chloride dissolved in sixty parts of water. But many persons prefer to add a very small proportion of gelatine ; but it is not desirable that the proportion used should exceed two parts to each hundred parts of the solu tion. The addition of gelatine is especially useful in the case of a paper which has not been highly sized, as the colloid matter tends to prevent the rapid penetration of the sensitizing solution, and the consequent production of pictures so deeply seated in the substance of the paper as to appear weak an I flat. A sixty or seventy-grain bath should be used for sensitizing, and two minutes is a suffi ciently long time for floating the paper, the prolonged action of the sensitizing solution being especially undesir able, as flat pictures naturally result. SOME OF THE USES OF COMMON ALUM. A substance very much used by photographers of late years—in fact, so much used that no well-appointed labora tory could be considered complete without it—is the sub stance known as common alum or potash alum, being a double sulphate of alumina and potash; but it is interest ing to note that much of the commercial alum met with at the present time is ammonia alum, or the double sulphate of alum and ammonia. It is quite a matter of indifference to the photographer whether he uses potash, alum, or ammonia-alum. Besides its great value to the Autotype, Woodburytype, and mechanical printers as an agent for hardening the gela tine films, it has been recommended for all sorts of ail ments photographic. The silver printer adds a small portion to his sensitizing bath to keep it in working order, and to prevent blistering of the albumen ; then, again’ silver prints are soaked in a dilute solution of alum, having for its object the thorough elimination of the last traces of the fixing salt. A very good proportion to use for this latter purpose is four fluid ounces of a saturated solution, diluted with one gallon of water, the prints being well agitated during an immersion of ten minutes. Of all the uses to which alum is put, perhaps uot in any single instance can so much satisfaction be derived as when it is used to arrest frilling of gelatine plates. This it has the power to do instantaneously, and many of the most careful workers, both amateur and professional, or at least those who do not care to run any unnecessary risks with negatives which have cost them a good deal of anxiety and trouble to secure, but prefer to make assurance doubly sure—such individuals may be numbered by the hundred — make it a point in every-day-practice to immerse all their plates in a solution of alum, either before fixing, or immedi ately afterwards. In fact, some operators have two alum baths in use: one a normal bath, as above-mentioned, for im mersing the plates in when of the ordinary printing inten sity; and the other a saturated solution strongly acidified by means of a vegetable acid (such as citric), or a mineral acid (such as sulphuric), for use when there is too much print ing density, since it has been found in practice that an acid solution of alum in contact with sodium thiosulphate on the gelatine image (after fixing, but before washing) not only removes the colour or stain caused by the alkaline or pyrogallol, but perceptibly reduces the strength of the image. Moreover, the colour does not again re-appear after washing, as it does sometimes when the fixing salt