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The photographic news
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- 24.1880
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- 1880
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- Bandzählung
- No. 1160, November 26, 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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November 26, 1880.] THE PHOTOGRAPHIC NEWS. 56? such as Indian ink, or alizarine ; in’summer one-fifth to one sixth gelatine to water, in winter more water. The ink is kept warm in the water-bath we have spoken of. Lastly, here is the filigrain process. “I call this the cheapest photographic image ever made,” says Mr. Wood bury ; he takes a carbon print developed on paper, hard and dry, of course, and sends it through the little rolling-press, in company with a sheet of plain paper. The consequence is that when the latter comes out, it has a water-mark of the same design as the carbon print with which it has been pressed in contact. Any design may be thus impressed. Here are visiting-cards with the portrait of the visitor to be seen if you hold them up to the light; writing-paper with all sorts of fancy designs; trade, marks, labels, &c. Filigrain, if it is the simplest, is also the most fascinating of Woodbury type applications. The “ At Home ” next week will be, “ Brighton in the Season.” far No. 154 300 Read before the Photographic Society of Great Britain. 2nd day. 2’3 1-7 2'3 30 3rd day. 3'00 2'7 3'00 8-00 1st day. 1 1 1 1 NOTES ON THE GELATINE PROCESS. BY CAPTAIN W. DE W. ABNEY, R.E., F.R.S.* I rave not seen the following observation in print, nor, as as I know, has it been investigated, so I have thought it worthy the attention of the Society. When my gelatine emulsion is prepared I invariably coat two or three small plates, and allow them to dry, and try them to see what qualities the emulsion possesses. In every case I have found the trial plates slower and less dense than plates which have been prepared the next day. I consulted Mr. England about the matter, and he informed me that he found the same thing with his emulsions. Now, till lately, I laid this down to the fact that, in the one case, the drying of the plates was slower than in the other ; thus the small plates would dry quicker in the drying cupboard, since the air must remain moister where a large number of plates are collected in the same space. Since my return from abroad I have, however, made fairly exhaustive experiments in regard to this subject, and find that drying has nothing to do with the matter. About ten batches of emulsion have been prepared and submitted to testing by that very useful instrument, War- nerke’s sensitometer, and also by taking transparencies from a standard negative. I tabulate some of the results :— Sensitiveness. No. 150 Emulsion ... No. 151 No. 152 " No. 153 ” am not at present able to answer the query, but shall endeavour to do so. In connection with this subject, I should be wrong not. to allude to a negative shown me by a member of our Society, Mr. Stenning, some months ago. One-half was coated immediately after the emulsion was prepared, and the other half coated, I think, ten or twelve days afterwards. The half of the plate coated with the emulsion when freshly prepared was neither so dense nor so fully-exposed as that coated later. I never gave a thought to the matter at the time, but now it is full of significance. Another point to which I would call attention is the fact that no plates that frill should be rejected. In July of this year I prepared a batch of some three dozen plates, and the weather being warm, I suppose the gelatine, to a certain degree, became decomposed, and the plates frilled viciously, and when coated with collodion blistered. The plates were put away till a few days ago, and tried. The film now is hard and tenacious, and when washed in water, and developed with developer at 75°, are No. 154 „ 1 ... 23 ... 300 So I might go on and recapitulate all my experiments ; but this will show what degree of extra sensitiveness is imparted by keeping an emulsion. It has been suggested that this sensitive- ness is gained through heating the emulsion twice or three times, to dissolve it; but this is not an explanation. Separate portions of the emulsion were kept undissolved, often for different periods, and then dissolved. The plates showed a similar gain in sensitiveness as when the emulsion was warmed up, day after day. The question arises, then, What is the cause of this ? I equally good. The film is prepared with a trace of chrome alum, which may be one of the causes of the cure for the evil, since keeping a gelatine film in contact with such a trace does render it insoluble and impervious. How badly the gelatine was decomposed may be judged of when I say that the plates, after fixing, are dry in less than ten minutes. Some commercial plates which I had eighteen months ago, and which were at the time incorrigible “ frillers,” saw the error of their ways after being kept in confinement for some six months. This observation is not new—at all events, I have heard it or read of it—but I thought it might not be amiss to recall it to the notice of the Society. Still another point to which I would direct you attention is, that in the development with ferrous oxalate, a judicious mix ture of a few drops of hyposulphite of soda will often bring out an image full of detail when a plate is apparently under exposed. 1 must, however, warn my readers against supposing that any plate is amenable to this treatment. When the plate is composed of silver bromide alone, or silver bromide and chloride, the effect of adding hyposulphite may be to cause a reversal of the image. When silver iodide enters into the com position of the emulsion, then the plan may be effective. I say may be, because I know that with some persons the addi tion has not been noticed to bring out more detail than they have had before on a plate.* Also I may remark that my experiments were made with the ferrous oxalate, not made from two solutions (which is wrongly called Eder’s developer), and also that the plates had a glossy surface, and not a matt surface. With such plates I have no hesitation in saying that the exposure required when the hyposulphite was used was at least one-third that required when it was omitted. This is how the observation arose. In developing a plate, which seemed decidedly under exposed, with ferrous oxalate, I happened to touch a bubble over the image with my finger, and where my finger touched, an image full of detail sprang out. Eveiy effect must have a cause, and the cause was hyposulphite with which my fingers had been previously in contact. The addition of a few drops to the developer gave an image full of detail. Other experiments confirmed the value of this addition. I W'ould ask the members to try it and report. I find the hyposul phite is best added after the film has been impregnated with the developer. One word more and 1 have done, and I dare say what I shall say now may be no novelty; but I would venture to recommend the method of intensification for gelatine plates which I have already printed in my book on the practical working of the gelatine process. Quite recently I have enlarged my experience with it, and can conscientiously say that it has not failed me once of late, which I lay to the fact that I am using peroxide of hydrogen which is fresher than that which I used before. It comes to this : after fixing your plate, wash it for half-an-hour in fresh water, changing every ten minutes, and then add 2 drachms of a 10 volume solution of peroxide of hydrogen to about 8 ounces of water, and let the plates soak in this for half-an-hour; wash again for five minutes, and then intensify with pyrogallic acid and silver— No. 1. Pyrogallic acid ... 2 grains Citric acid ... ... ... ... 2 ,, Water ... ... ... ... I ounce No. 2. Silver nitrate 20 grains Water ... ... ... ... 1 ounce Add about half a drachm of No. 2 to every 2 ounces of No. 1, and intensify in a dish till proper intensity is reached. Negatives which gave only a phantom image I have intensified to good printing density, and without a stain or blemish of any sort. I shall be glad to demonstrate the proceeding, if thought advisable, at any of our meetings. I may say that 1 now prefer pyrogallic acid intensifier to ferrous sulphate and citric acid. I recommend that intensification should take place either in the dark room or a room weakly lighted with white light ; a bright light is apt to cause mischief. Gelatine plates with matt surfaces seem to take both intensity and also development more kindly than to those with glossy surfaces, and my aim now is always to prepare plates in that condition. I have ventured to bring forward these observations on the first evening of the session, as it is a night on which no discussion is advisable, and I believe that none can arise on the subjects I have introduced. • From what I have since heard, the plates were fully-exposed, hence no benefit would arise from the addition of the hyposulphite.
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