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The photographic news
- Bandzählung
- 12.1868
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- 1868
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 516, July 24, 1868
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Zeitschrift
The photographic news
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Band
Band 12.1868
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- Titelblatt Titelblatt I
- Kapitel Preface III
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- Register The Index To Volume XII 619
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356 THE PHOTOGRAPHIC NEWS. [July 24, 1868. A few points in ison’s remarks on this suppose that a picture possesses ; in an over- * Photographischa Archil'. 2 grammes 100 „ extremes there should be as many gradations of tone as possible. If few half tones only are present in the negative it is impossible to obtain a brilliant print from the same, as the result will either be weak, or hard, according to the difference in the thickness of the film in the lights and shadows. grey. In developing a plate which has been exposed too long, it is best not to allow the developer to go too far, but to wash as soon as symptoms of over-development are recognizable: in this manner many a picture may be saved. Very much to the point are Simpi subject. He says: " Let us suppose t twenty different gradations of tone; in order to be able to which is added by drops to the silver solution (shaking the latter the while) until a slight turbidity is observed. The bath is then exposed to the sun for a few hours, or to open daylight for some time, when a black precipitate will be formed, which is filtered off. For every hundred grammes of bath is then added 1 drop of acidulated water made by mixing 10 grammes of sulphuric acid with 100 grammes of water. After standing for some hours, the following test should be made :—Coat a plate with collodion, sensitize it, and let it drain well ; develop it in the ordinary manner, without exposing, and wash and fix the plate as usual. After fixing, if the glass is not perfectly clear, but is still covered with a thin, light deposit which may be removed by the finger, a few more drops of acid must be added, and the experiment repeated : too much acid must never be added at any one time, and care must be taken that the plates used in the experiments are perfectly clean. As the deposit upon the plate may likewise be caused by the action of light, all chemical rays must be carefully excluded from the dark room. The addition of organic substances to the developer is ex tremely favourable to the production of brilliant negatives. The three following formulae are recommended :— be found in relief. It is better then to make a cast of it and pile up the white parts. The cast may be stereotyped or electrotyped in the usual way. The process has been practised in France for ordinary work, and, it is said, with success ; but I do not think it has been used in conjunction with photography. Caustic potash Water ... furnish a good print, the negative must then be composed of twenty different thicknesses of deposit, which are visible when the image is seen by transmitted light. A negative which begins with perfect transparency, presenting no hin drance whatever to the light in the production of the deepest tones, and which possesses the twenty gradations of tone, is capable of giving a perfectly brilliant result, although it may not appear very opaque in its highest lights. But if the deepest shadows are covered with a deposit equal to ten gradations, then the film in the highest lights must be of a thickness equal to thirty gradations of tone, in order to be capable of producing a good print; if the film in the highest lights is equal in thickness to twenty-five gradations of tone only, it will give less brilliant pictures than the negative first mentioned, although the film may at first sight appear of greater thickness.” Under-exposed negatives generally give hard pictures with large masses of white and black, and without detail or half tones. Over-exposure causes a grey precipitate to cover the picture, which fogs the shadows ; a print produced from such a negative is too light in the shadows and too dark in the lights, for everything is lost in half tone, and brilliant lights and deep shadows are wanting ■ in an over exposed negative a black coat becomes grey. Ir With regard to the latter, tho gelatine is dissolved in the acetic acid and 50 grammes of water (this will take several hours), and the sulphate of iron dissolved in 250 grammes of water, and both solutions are then mixed. In general it will be found that weak developers produce opaque negatives, and strong developers negatives of an harmonious character. No. II. developer is suitable for summer work, and for strongly-lighted pictures. The developer should be used sparingly, for the employment of too much solution impairs THE WET COLLODION PROCESS. Remarks upon the Production of Brilliant Pictures. BY C. STERNBERG.* A brilliant negative is the first thing needful in obtaining brilliant pictures. Every possessor of a portrait album must have remarked how comparatively few of the pictures in his collection have any pretension to brilliancy. Many photographs are sharp and full of detail, but at the same time dull and without vigour, or they are sharp and clear, but hard, apd without either detail or half tone. But few specimens are plastic and brilliant, and have sufficient grada tion of tone. A process by which brilliant negatives are obtainable includes, of course, many manipulations with which the ex perienced photographer is perfectly familiar ; but, neverthe less, to the general reader, a recapitulation of the different conditions necessary to their production may not be without interest. In my opinion, the great source of failure lies in the thick ness of the film which forms the image upon the glass plate. Although I am perfectly aware that the negatives of many excellent photographers possess a certain amount of thick ness, still I am, nevertheless, of opinion that a really good negative should be thin and perfectly clear. A few points in the deepest shadows should display clear glass, and in certain portions of the high lights an almost perfect opaque ness of the film should be visible; and between these two The collodion to be used must not be too freshly mixed, and should be perfectly clear ; its consistence should not be too thin, and it must be sufficiently iodized. Thick col lodion should be diluted with equal parts of perfectly pure alcohol and ether. The sensitizing bath must be prepared from recrystallized nitrate of silver, and should be rendered slightly acid in order to produce perfectly transparent shadows ; too much acid exerts the same injurious effect upon the negative as too little. One part silver dissolved in twelve parts of water is a good proportion for making a bath ; a saturated solu tion of iodide of potassium is prepared, and to every 400 grammes of silver solution is added one diop of the iodide and one drop of strong sulphuric acid, as under:— Nitrate of silver ... ... 30 grammes Distilled water ... ... 300 „ Strong sulphuric acid 1 drop Saturated solution of iodide of potassium 1 „ If the water and chemicals used are perfectly pure, this bath will give beautifully clear negatives ; but should not this be the case, and there is formed upon the picture a grey deposit, capable of being removed by the finger, the bath is purified with a solution of— I.—Sulphate of iron 25 grammes Loaf sugar 40 „ Glacial acetic acid ... 15 Water 500 Alcohol 15 II.—Sulphate of iron 10 grammes Loaf sugar 40 Glacial acetic acid 10 Water 400 Alcohol 1 gramme III.—Sulphate of iron and ammonia 22 grammes Gelatine 1 gramme Glacial acetic acid 8 grammes Water 300 „
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