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THE PHOTOGRAPHIC NEWS. Vol. XXVII. No. 1319.—December 14, 1883. CONTENTS. PAGE A Modification of the Alkaline Developer 785 Fire-Proof Photographs 785 Gelatino-Bromide Paper for Positive Pictures 786 “ By-tbe-Bye"—How to Copy a Faded Photograph “87 The Crayontype: A New Photo-Grain Process. By Ad. T. Eggis. 789 Abstract of Mr. C. Ray Woods’ Lecture 789 A Few Remarks on the Platinotype Process. By W . B. Allison 791 Notes 791 PAGE Patent Intelligence 793 Developing Gelatine Pe'ats. By E. Brightman 794 Photo-Lithography and Photo-Zincography. By Major J. Waterhouse, B.S.C 795 Correspondence 796 Proceedings of Societies 796 Talk in the Studio 799 To Correspondents • • 800 The Photographic News Registry 800 A MODIFICATION OF THE ALKALINE DEVELOPER. OUR readers know that the ordinary developer containing ammonia, bromide, and pyro, does not possess permanent alkalinity, for its strength is liable to variations on keep ing, on account of the first-named constituent, ammonia. Some of the ammonia gas is sure to find its way out, and the solution deteriorates in strength. The necessity for the presence of some alkali is, we need scarcely tell our readers, to increase and to hasten the reducing power of the pyro. The re-agent used to accomplish this end when pyro is used in the laboratory for determining the quantity of oxygen in a gas analysis is caustic potash. As long ago as seven years, the use of caustic potash in alkaline development was discussed by Captain Abney, and we have been able to successfully develop many plates by means of the alkaline hydrates, but we wish first to point out what may be important applications of them. We wish to show how these hydrates of potash and soda may be turned to account, while those who prefer the use of ammonia may still have the pleasure of using it. Caustic potash and caustic soda are more powerful alkalis than ammonia, and are capable of turning ammonia out of a combination. If caustic potash be added to a solution of a salt of ammonium, ammonia is set free, and may be recognized by its smell. To apply this to purposes of development, we made up the following solutions :— Pyro Solution. 1} grains of pyro to each ounce of water. Bromide Solution. Bromide of ammonium 35 grains Water 1 ounce Alkaline Solntion. Caustic potash ... ... ... 20 ounces Water 1 ounce The last two solutions are calculated to be of the relative strengths necessary to form, by adding them in equal proportions, potassium bromide and ammonia by double decomposition. In fact, providing the chemicals are pure, if the relative quantities by weight of the two com pounds are as 7 to 4, there should be neither bromide of ammonium nor caustic potash in a mixed solution ; but a slight variation in the chemical purity will not affect the practical result. Trying this first on a quarter-plate that had received the usual exposure, we took one ounce of the pyro solution, and ten to fifteen drops each of the bromide and alkaline solu tions. The image came up quickly, and reached good density. By varying the exposure, and with it the propor tions of bromide and alkali, we were also able to get successful results. The plates we used registered 24 on Mr. Warnerke’s sensitometer, and gave good images. It is not easy to give a formula which will suit every class of plates, and each manipulator, of course, prefers to suit his own taste in this respect; but, with ordinary exposures, good results may be obtained without using the alkaline solution in a larger proportion to the bromide than is necessary to produce complete double decomposition. A larger proportion of the caustic potash may be used if required: but, in that case, we are no longer using the ordinary developer. It is a question mooted now and again, whether we cannot get rid of the use of ammonia altogether, and re lieve photographers of the inconvenience arising from its fumes during development; and here we come back to a matter already touched upon, the use of caustic potash in place of ammonia, no ammonium salt being used. It was in this direction that we first experimented, and with success. The following was the formula we used :— Pyro Solution. 1} grains of pyro to each ounce of water. Bromide Solution. Potassium bromide 20 grains Water ... ... ... ... 1 ounce Alkaline Solution. Caustic potash 20 grains Water ... ... ... ... 1 ounce To one ounce of pyro we take fifteen drops of potassium bromide, and commence development with five drops only of the alkaline solution, adding more if required. This developer, with two kinds of plates on which we have used it, gives good results, but more pyro stain was observed than with the other formula given. This increase of stain is also a defect of the potash carbonate developer, but it may be removed by an application of the clearing solution of alum and citric acid. We have not yet succeeded in get ting green fog with this developer, even on forcing the development of an under-exposed plate; a large excess of caustic potash only brought about increased pyro stain. We have not yet tried sulphite of soda with either of these developers. FIRE-PROOF PHOTOGRAPHS. An ordinary carbon print is permanent in the sense that the pigment of which the image is composed will not be come changed or destroyed by many of these agencies which gradually obliterate a silver print, but a photograph which will not only withstand time, light, and moisture, but also fire, is permanent in a much more extended degree.
