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The photographic news
- Bandzählung
- 35.1891
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- 1891
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1714, July 10, 1891
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The photographic news
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Band 35.1891
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500 THE PHOTOGRAPHIC NEWS. [July 10, 1891. A NEW EMULSION FOR PRINTING-OUT PAPER. BY PROFESSOR w. K. BURTON. I remember once talking to Mr. W. B. Bolton, to whom we owe so much for our present knowledge of emulsion work, on the genesis of collodio-bromide emulsions. He told me that one of the suggestions came from Rejlander. This artist was always in trouble with his bath, or his collodion, or both, and, speaking with Mr. Bolton and some other experimentalists, he asked, “ Cannot some of you clever fellows get over this eternal bother by mixing the whole lot up together?” Well, a collodion emulsion may be looked on as a mixture of the collodion and the wet plate bath. The water is the only thing that is left out, and not the whole of that. Something of the same thing suggested itself to me some time ago in connection with printing. I had been trying various different ways of sensitising plain paper with silver salts, trying, amongst others, some of the excellent pro cesses of Mr. Lyonel Clark, and I got good results with many of them, if I gave the necessary amount of care and took trouble enough ; but the care needed was certainly great, and the trouble of the double process of salting and sensitising more than I liked. Moreover, I found that I was very liable to get defects in the way of spots, streaks, and the like, even after all the care and trouble. Why not, I thought, get over at least half the trouble by mixing the ingredients up together and applying them to the paper in one operation? Every formula that I had been using contained gelatine as one of the constituents, and had the making of an emulsion in it. There is nothing new in this, it may be said. It is nothing more nor less than the gelatino-chloride emulsion that we are already acquainted with under various names, such as " aristotype,” and goodness knows what else. I think, however, that the emulsions that I am going to de scribe have several novel features. In the first place, they are emulsions that need no washing, and that are made by the extremely simple process of pouring one liquid into, or mixing one liquid with another. The emulsions are, moreover, ready for use at once, and, being liquid at ordinary temperatures, can be applied to paper or other materials either by floating, as in the common method of sensitising albumenised paper, or by brushing them over the material that it is wished to sensitise. Farther than this, no gloss is given to the surface of the paper. I think, indeed, that by this process the preparation of sensitised paper—of any kind so far as surface is concerned—is reduced to the utmost possible simplicity. I have tried a number of variations in the quantities of chemicals, and have had more or less success with all. In fact, there is great elasticity in the proportions that may be used, and I believe that almost any formula for a printing-out gelatino-chloride emulsion might be taken, and that good results could be got if one or two considera tions were not lost sight of. The first is that the quantity of gelatine must be kept so low that it will not cause a gloss on the paper, or cause the emulsion to set at ordi- nary temperatures. The second is that the formula must insure a large quantity of insoluble silver salt in suspen sion. The reason for this is that the coating got by an emulsion that does not gelatinise immediately after coating is much thinner than if it does gelatinise. To those who have not had much experience in emul sion work, it may be worthy of remark that, within very wide limits, the same quantity of an insoluble silver salt is emulsifiable in a given quantity of water, whether the quantity of gelatine used as a menstruum be great or small. Roughly speaking, the haloids, or I imagine the other insoluble or nearly insoluble salts of silver, result ing from the decomposition of one ounce of silver nitrate, can be emulsified in ten ounces of water, but if that quantity of silver be exceeded a part will not emulsify, but will be thrown down in the granular form, in which it is useless for sensitising any surface. The proportions vary, however, with certain conditions—such as alkalinity or acidity of the solutions. The difference between the failure of a silver haloid to emulsify in a gelatinous solution, and the precipitation of it from that solution afterwards, must not be lost sight of. Thus, if any of the emulsions that I am now writing of be kept for a number of days at a highish temperature—such as that of pretty hot weather—it is likely that a good deal of the insoluble silver salt will be found at the bottom of the vessel holding the emulsion, but this silver salt is not in the granular state, and can be re-emulsified by heating the mixture to about 120° Fahr., and shaking well, the more easily if a little more gelatine be added. I select three formula as follows:— Formula A.—Nitrate of silver ... Water ... No. 1. 400 grains 4 ounces B.—Gelatine (soft) ... Chloride of ammonium ... Citric acid Water • 80 grains 80 >> 120 ,, 8 ounces Formula A.—Nitrate of silver ... Water No. 2. 400 grains 4 ounces B.—Gelatine (soft) Chloride of ammonium ... Citric acid Carbonate of soda (dry) ... Water • * • • • 80 grains 80 „ 120 „ 45 „ 8 ounces Formula A.—Nitrate of silver ... Water ... ... No. 3. 400 grains 4 ounces B.—Gelatine (soft) ... ... Chloride of ammonium ... Citric acid ... ... Carbonate of soda (dry) ... Water ... ... ... 80 grains 80 „ 60 „ 80 „ 8 ounces In my hands the first formula gives an emulsion suitable for preparing paper to be used for printing from dense negatives, the second from medium negatives, and the third from thin negatives. The third formula is, I am afraid, dreadfully unortho dox. Unless I have made a mistake in my chemistry— which is highly probable—there is just about enough of ammonium chloride and of sodium citrate formed by the double decomposition of the citric acid and of part of the soda to decompose the whole of the nitrate of silver. I don’t know whether, in this case, there will be carbonate of silver formed; but if not there remains a large excess of carbonate of soda. All I can say is that the formula works all right, and that the paper that results from the use of it keeps very fairly. The paper resulting from either of the other formula; will, I have no doubt, keep as long as any ready sensitised paper. I have already kept some nearly a month, and it is still quite white. The following is the method of emulsifying. The two solutions are heated to a temperature of 110° to 120° Fahr. The temperature should not be greater than 120°, or there
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