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The photographic news
- Bandzählung
- 29.1885
- Erscheinungsdatum
- 1885
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- Englisch
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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. 1398, June 19, 1885
- Digitalisat
- SLUB Dresden
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- Parlamentsperiode
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Zeitschrift
The photographic news
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Band
Band 29.1885
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- Register Index III
- Ausgabe Ausgabe 1
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Band
Band 29.1885
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- Titel
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THE PHOTOGRAPHIC NEWS. [June 19, 1885. 390 fastened to the wall, the use of which has been patented by me for photographic purposes. On the swinging arm of the crane I fix cross beams with several rows of small sources of light, as, for instance, Argand burners of sixteen normal canales, over which suitable reflectors, either of glass or metal, are placed. These lights spent a good top light. At the end of the crane arm a reflector is fixed which is similar to a prompter’s box. This reflector has posted in its midst a powerful regenerative Siemens’ gas burner of about 250 normal candles. To enlarge the re flecting power of this reflector, it is lined inside with thin sheet iron nickled or tinned and polished. The bottom is closed by a movable screen of the same material. Above this reflector, I place a row of Argand burners with reflec tors, which are fastened diagonally against the same, so that they spent their light downwards. In this manner the rays of light cross themselves many times, so that no heavy shadows can be formed. To lead off the products of com bustion, a pipe is fastened to the crane, which is in con nection with another one leading to a chimney. At the same time, ventilation for the room must be provided for. The heat which is occasioned by the burning of many flames may be considered lowered by turning the main part of the gas off when no sitting takes place. All the burners can be regulated separately, and also it is possible to regulate the whole of them at once. The crane can be easily turned by a lever movement with the aid of a crank, which is fastened sidewards out of the way. Not alone that it is possible to give different poses of illumination ; the system can be used after having the desired illumina tion selected, either by using the system in a fixed posi tion, or by moving the same during the exposure. It can be easily comprehended that many different methods of illumination can be made in this way, also even Rembrandt effects. Of course it is very necessary to work with rapid lenses, large stops, rapid dry plates of 24 Warnerke. The expo sure is about twenty seconds. I also recommend to deve lop in the following manner, which has been found out by me, during the trials of all kinds of developers, to be the best method. Those artists who take views of interiors, as well as instantaneous views, and those who make nega tives by artificial light, must have observed that the deep shadows are inclined to remain glossy without details. To obviate this, I bathe the plate before developing in a solu tion of hyposulphite of soda in water (1-2000 of water), and add one drop of a saturated solution of corrosive sub limate. I leave the plate in this bath for two minutes ; longer is not advisable, also no stronger solutions. This bath makes that when the plate has been washed, and afterwards put into the developer of iron oxalate, 1 :3 (Dr. Eder), the deep shades develop instantly together with the high lights, so that during the development the negatives can be easy controlled. Never mind that at first the plates seem to be dull; they gain strength by-and- bye in developing, and all the deep shades are brought out. After developing, I wash and fix as usual. JOTTINGS. BY MAJOR J. WATERHOUSE, S.C., Assist. Surveyor-General of India. formation of Fulminatiug Silver from Mirror-Silvering Solutions.—Apropos of the editorial remaks on silvering mirrors at page 225 of the present volume of the News, it may be well to warn incautious operators of the danger of leaving the mixed silver ammonia and potash solution to rest for any time before use. It recently happened here, that after the silvering solation for a 9-inch mirror had been mixed up, the deposition had to be postponed for about twenty-four hours, at a time when the weather was unusually hot. It was then found that the sides and bottom of the beaker containing the solution were thickly coated with a dark coloured precipitate. The solution appeared to have decomposed ; it was thrown out and pre cipitated to recover the silver. The beaker was filled up with water, and put aside to be cleared with the mixture of nitric acid and bichromate of potash usually employed for that purpose. As, however, the dangerous nature of the precipitate was suspected, it was touched very cautiously with a drop of the solution at the end of a glass rod, with the immediate result of a violent explosion, which, fortu nately, did no further damage than shattering the beaker. Investigation showed that the precipitate was the ammonia oxide of silver, or Berthollet's fulminating silver, an ex ceedingly dangerous compound, which may explode at the slightest touch, even in a moist state. Care should, there fore, be taken to use the solution as soon as mixed, and to quickly clean the vessels containing it. On a previous occasion a somewhat similar accident happened with a glass that had been put aside dirty and forgotten. In this case pouring in nitric acid produced an explosion. Use of Silver Precipitate in Electrotpying.—In connection with the silvering of mirrors, it may be mentioned that the fine muddy precipitate which falls to the bottom of the dish during the silvering has been found to be an admirable material for rendering electrotype moulds con ductive. The use of precipitated silver for this purpose is well known, but the precipitate thus obtained is much finer than that formed by copper in solutions of nitrate of silver, and takes beautifully on wax surfaces. It is also useful with gelatine or other surfaces, applied either dry or in a moist state, and brushed off after drying. It may also be mixed with plumbago. Wax Compound for Moulding from Gelatine.—An excellent substance for making moulds from moist gelatine is the wax composition recommended some years ago in the Correspondenz for 1874, p. 185, by Herr Leipold, of the Bank of Portugal, Lisbon, in connection with the Pretsch process of photo-engraving. It is as follows : — Spermaceti 425 parts Stearic acid 200 „ White wax 170 „ Asphalt 70 „ Plumbago 70 ,, The asphalt is first melted, then the spermaceti wax and stearin are added, and finally, when by constant stirring all have become fluid, which they quickly do with a heat of about 190° F., the given quantity of graphite is mixed in. The advantages of the composition are—its melting at a moderate heat, and consequent easy hardening on the soft relief. It hardens completely after cooling, and is not injured by brushing with plumbago. It separates easily from the gelatine relief. It is also useful for moulding from medals, the latter being previously rubbed over with a little glycerine; instead of spermaceti, paraflin maybe used. Hie New Development Printing Process in India.—It may be interesting to Indian readers of the News to know that the new process is quite suitable for uso in India, and is not much more trouble than the old method, while there is a far greater chance of the prints being permanent, and in this case any extra trouble is of small account. I have not yet had much experience of the process, or the opportunity of trying the various developers recom mended ; but Morgan’s developer, as given at page 109 of this year’s News, seems to answer very well. With the Alpha paper an exposure of two to three seconds in bright diffused daylight in a verandah, for a gelatine negative of ordinary density, gives good tones in the double fixing and toning bath recommended by Warnerke in a recent- number of the News. Dense negatives will require more exposure to get good tones, and thin ones less. It is noticeable that the accidental touching of unfixed prints with fingers wet with hypo from the toning and fixing solution is not followed by such dire results as in
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