The photographic news

• Bandzählung: 35.1891
• Erscheinungsdatum: 1891
• Sprache: Englisch
• Signatur: F 135
• Vorlage: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: SLUB Dresden
• Rechtehinweis: Public Domain Mark 1.0
• URN: urn:nbn:de:bsz:14-db-id1780948042-189100009
• PURL: http://digital.slub-dresden.de/id1780948042-18910000
• OAI: oai:de:slub-dresden:db:id-1780948042-18910000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

514 THE PHOTOGRAPHIC NEWS. [July 17, 1891. sides white, the resulting picture combined sharpness with softness and relief, especially on the part towards the black sides. If the bottom of the camera was black it added to the clearness of the face ; if the top of the camera was dark the clothing was clearer. Consequently, as the face in relation to the drapery usually has too much light, better results were obtained when the top and sides were white, and the bottom black. As will be seen from all the above suggestions, no precise method has been evolved which could be adopted in regular practice. 2. Primary and Secondary Liyhting of Gelatine {Bromide of Silver) Dry Plates.—Gelatine dry plates may also be im proved during development if the necessary caution is used. It is, perhaps, superfluous to remark that with the greater sensitiveness of the gelatine dry plate, it is much more difficult to gauge the correct time for supplemental lighting than with the wet collodion plate, and the diffi culty of preventing fog is greatly enhanced. With extra rapid dry plates the period of the primary action is so exceedingly short that even with a slight light impression a developable image is obtainable, and even the shortest lighting causes a general reduction (fogging). On the contrary, on less sensitive, clear-working plates a marked effect is shown by additional lighting. Candle light can only be used for this purpose at a very great distance, or when greatly weakened. According to Eder, candle-light worked better when thrown through a ruby glass. His experiments showed that in a slow dry plate of 15 Warnerke, after being exposed from two to six min utes immediately in front of a ruby lamp (candle-flame), the sensibility was raised to 19-20 Warnerke sensitometer, which was equal to a plate three times as sensitive. E. Himly, in Berlin, patented a so-called (Hilfsbelichter) auxiliary exposer, which introduced diffused light into the camera (D. R. patent 38, 684, August 6th, 1886) ; vide Eder’s Year-book, 1889, p. 87. Preliminary light ing with dry plates of high sensibility is partly unnecessary, partly dangerous, and therefore is not advisable in actual practice. In all probability the same results obtained on gelatine dry plates by auxiliary exposure may be reached in a purely chemical manner without the action of light. A minimum reduction of silver bromide must be intro duced. This takes place by extending the so-called ripening process. In fact, the continuation of the diges tion of the emulsion leads to fogging, and otherwise it is exceedingly dangerous to the rapidity of the emulsion, when treated with reagents, which are apt to change the reduced bromide (sub-bromide) back to its normal con dition. At the conclusion of the reading, Mr. Carbutt inquired on what date the first coloured diaphragm was used in the lens. Mr. Sachse said he did not know the date, but it was first used by Guillard. Mr. Carbutt stated that he had used a coloured diaphragm in 1858 or 1859. He was then working in a small gallery in a small way, in an interior town in Indiana. They were using the wet collodion process at that time. He used a blue diaphragm, and obtained a sharp picture in about the same time that would have been required by a very much larger aperture. Mr. Bell said that in 1872 the photographer of the Treasury Department and himself instituted a series of experiments in preliminary lighting. The plate was exposed from three to five seconds with a red glass in front of the lens, and then exposed on the sitter. The result in all cases was less valuable than if they had not exposed to the red light at all, but had given it proper time. It might be useful where a man’s chemicals were in a very insensitive condition, as it would help him to make a much better picture than he could otherwise obtain. He had also used the blue light, by apertures in front of the box, and again in the cap, and after exposure swung in front of a white screen for an instant. At that time he had slow light, and this method helped him very much to get certain pictures, such as children. Still, the results were never very good, not as perfect as would have been the case had he been able to expose the proper time. The Chairman inquired which colour gave the best results, the blue or the red. Mr. Bell replied that in the preliminary lighting he found the red glass was the best. Mr. Cheyney said that it seemed to him they all used this preliminary, &c., lighting. While it was not intentional, they all did exactly what Mr. Sachse had described. In the first place, they took out their plates in a dark room lighted by red light, dusted them, and inserted them in the holders ; that was the preliminary lighting. Then they exposed the plates; that was the secondary stage. Next they developed under the red light, and if the development did not proceed fast enough they held the plate up close to the red light to see what was the matter. That was the supplemental lighting. Hence, they all did what Mr. Sachse had described. In reply to a question from the Chairman, Mr. Sachse said the red light employed was merely the ordinary red light of the lantern. The Chairman asked where, then, lay the difference between this red light and that used in ordinary development. Mr. Sachse stated that it differed in this respect, that he personally always filled his holders in the dark. Then, after exposure, he never subjected the plates directly to the red light of the developing room, but put them in the pan in the shadow, and, after a few minutes, held them to the red light to see if the image had appeared. He was always very careful to keep away where the exposure was normal. Mr. McCollin said he recollected one of the members, Mr. Browne, in the old collodion-emulsion days, brought to him some undeveloped plates ; and they were made into fairly good plates by means of candle-light. They were developed in a yellow glass dish. Mr. Cheyney explained the test he made of his lantern. He exposed a 26 Seeds plate before the lantern for five minutes with a figure cut from cardboard in front of it, and could get no image—the plate was perfectly clear. So he came to the conclusion that he was quite safe in taking his time in develop ment. Mr. Sachse remarked that he found a difference in the makes of plates. In one make of plates exposure to the lantern invariably resulted in fog. Two other makes he was in the habit of using always came out clear. The .Secretary inquired if this was really an improvement, or only a slight veiling which, as Mr. Carbutt said, made certain details apparent, or softened down the hardness of an under-exposed plate. Mr. Sachse’s experience had been that it did bring out detail. In speaking of the matter three years ago with a professional photographer, that gentleman attributed the improvement to pouring off the developer and leaving the plate exposed to the action of the air. He contended the ruby light had nothing to do with it, and said that when he found under-exposed plates he poured off the developer, exposed to the air, and then put them in the developer again. The Secretary said it seemed to him that plates grew in detail while being examined, as though the air, coming in con tact with the plate, might have that effect. Mr. Walmsley supposed every one working with a developer had experienced that. His own developer he kept on the plate only long enough to bring out the detail slightly ; he then poured it off, put a cover over it, and it would bring out a density in a few minutes so dark that they could not see through it. Mr. Ives stated that more density would be developed where the air came in contact with the plate than where it was kept from it. Mr. Cheyney mentioned an instance where he had allowed