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The photographic news
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- 24.1880
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- 1880
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- Bandzählung
- No. 1136, June 11, 1880
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The photographic news
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Band 24.1880
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- Register Index 631
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Band 24.1880
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282 THE PHOTOGRAPHIC NEWS. [June 11, 1880. vge Pkotograpgir Srbs, Vol. XXIV. No. 1136-—JUNE 11, 1880. CONTENTS. page Photography In. and Out of the Studio 277 At Home 278 The Oxy-Hydrogen Lime-Light. By Rev. T. F. Hardwich ... 279 Gelatine or Collodion—Which Pays Best? By John S. Hazard 279 Development of Bromide of Silver Plates. By Dr. J. M. Eder 280 Gelatine Plates for Landscape Work. By E. Dunmore 281 M. Janssen on the Usefulness of Photography in Science 281 Manipulation of Gelatine Emulsion 282 Fogging and Frilling 282 Notes 283 Topics of the Day 284 Correspondence 284 Proceedings of Societies 286 Talk in the Studio 288 To Correspondents - 288 MANIPULATION OF GELATINE EMULSION Whether it will pay amateur or professional photo graphers hereafter to prepare their own gelatine plates is a question that we need not now determine ; but certain it is that the majority will try their hands at producing the sensitive pellicle. The matter will ultimately resolve itself into one of money ; if photographers find that with a moderate expenditure of time and trouble plates can be made at home as good and more cheaply than those to be purchased, home-made plates will naturally be resorted to; on the other hand, those who set a high price on their labour, or have no time to spare, will be glad enough to purchase the emulsion or plates ready for use. Al ready the cost of plates in the market has been con siderably reduced—the price was absurdly high a little while ago—and with so many able makers engaged in the manufacture of gelatino-bromide, we are now getting more steady and equitable prices. The number of photographers who will continue to pre pare their own plates may therefore be limited, but at the present moment, nine out of ten would appear to have prepared the emulsion, or at any rate made experiments in connection with its preparation. We have, in these columns, repeatedly given formula) for gelatino-bromide plates, and have also said something of the manipulations involved; and it is in respect to the latter more especi ally that we would to-day have a further say. But first a word about the transparency of the gelatine employed in emulsion making. As a rule, the makers of plates will have nothing to do with gelatine that is slightly turbid. It must be perfectly clear, or they refuse it altogether. | It does not matter how tough or sound it is; if there is turbidity in the solution, they will have none of it. On the other hand, gelatine containing traces of hydrochloric acid fused in opening up the bones in gelatine manufacture) or of sulphuric acid (which is employed for bleaching) is not objected to, supposing a solution of it is perfectly clear. Now, we believe, that a slight turbidity is no drawback to an otherwise good sample of gelatine ; the film on the plate is so thin that the defect is really inappreciable. We have experimented with gelatine of an extremely turbid character—nay, even with isinglass—and, so far as trans parency of the film is concerned, have found no appreciable difference between it and that given by a transparent gelatine. The manufacturers of gelatine, we hear, are at their wits’ end to know how to satisfy photographers; the former have no difficulty in supplying a neutral gelatine which is a little turbid, or transparent gelatine with traces of acid, but they find it next to impossible to make a neu tral transparent material. Photographers, in taking a choice of the two evils, prefer to employ transparent gelatine. In adding the silver solution to the dissolved gelatine and bromine salts, care must be taken, as we all know, to do so very gradually. Some prefer to blow the warm silver solution from a chemist’s wash-bottle, others to per mit it to fall from a filter, with a drawn-out orifice, in a FOGGING AND FRILLING. The Photographic Society brought its session to an end with a most interesting meeting on Tuesday evening, Captain Abney and Mr. Bolas bringing foiward subjects . of considerable importance. Captain Abney pointed out that the oxidising action of bichromate of potash might bo employed with advantage to cure fogging in gelatine plates. A defective plate of this kind, or a gelatine plate that has been exposed to light, if flooled wi h a it ong solution of bichromate, and afterwards washed, may be con verted once more into a transparent sensitive film. Bad plates, he tells us, may thus be changed into good ones. We shall have some one now proposing to make gelatine emulsion in daylight, and leaving it unwashed until trans ferred to glass, when the application of a bichromate solution, and rinsing in cold water, will complete the manu facture. To prevent frilling—a defect, we are glad to say, that is met with less frequently than of yore—Captain Abney coats his plates with collodion ; this film of collodion does not impede the action of the developer in any way. fine stream. The burette will be found, however, a very handy piece of apparatus for this work, a wide tube fixed perpendicularly, having a tiny glass stop-cock at the bot tom, to control the falling stream. An instrument of this description, graduated in cubic centimetres, may be pur chased for three or four shillings, and will be found useful in the photographic laboratory in many other ways. In this case, the warm silver solution is introduced into the burette, and while stirring the gelatine with one hand, the stop-cock may be turned with the other. The silver solution may be permitted to fall by drops, or in a stream at inter vals. Moreover, as the silver falls into the gelatine solu tion, you are able, by means of the graduated scale upon the burette, to note how much has fallen, and to control the addition with the greatest nicety. Another point of importance is, of course, the well- stirring of the gelatine during the falling of the silver. We have found a modification of a chocolate stirrer to be a most convenient tool to use. In making from ten to fifteen ounces of emulsion, a stirrer, about the thickness of a lead pencil, but longer, answers the purpose well, and may be twirled in the fingers of one hand. For our purpose we employ wood, the end of the stick fitting into a cross or star, and have never known any injurious effects from its use. It is manipulated by one band only, and if the silver solu tion to be added is contained in a burette with stop-cock, this, the most difficult operation of all in connection with the preparation of gelatino-bromide, is considerably simpli fied. A hot-water can should always have a place iu the laboratory during the preparation of emulsion, and the stirrer is put in here when not in use; hot water is very necessary in warming flannels, filters, &c., with which the photographer has from time to time to deal. As to washing the emulsion, we are not so sure whether one of the very first suggestions made—namely, to employ a dialyser for the purpose—is not the simplest and best. A dialyser is nothing but a description of tambourine, or vessel with a membrane bottom. They are, now-a-days, used in the kitchen as a means of washing salt out of salted liquors or very salt soup, and photographers must not, therefore, suppose that they have a complicated apparatus to deal with. Emulsion placed in the dialyser, and this in water for twenty-four hours, is rid of its salts, if the water has been changed two or three times in the interval. Another simple way of washing is to construct a square framework with four laths, and stretch loosely over it a piece of blanket. The set emulsion is thrown upon the blanket, which is permitted to dip into cold water, and then broken up and manipulated with an ivory knife; if possible, the blanket should dip in running water, but if this is not the case, the water must be changed repeatedly during the half hour or so that the washing continues.
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