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

646 THE PHOTOGRAPHIC NEWS. [September 11, 1891. uncovered. Evidently the exposure under red was in sufficient. At the same time, this experiment indicates that a good relative proportion of the two classes of rays may exist in the magnesium light, such as would produce sufficient fog all over the plate through all parts of the superposed image, and at the same time be sufficiently active in oxidising rays to undo the work of the reducing rays where the plate is least protected. Experiment 11.—Preliminary exposed plate, as in Experiment 10, and exposed, without red tissue, to 8 in. of magnesium. Besult.—Thin reversal. Experiment 12.—Same conditions and result as in Experiment 11. Experiment 13.—Preliminary exposed plate for thirty seconds to candle at 6 in. ; then covered half the plate with blue tissue, and exposed to 12 in. of magnesium at 6 in. Eesult.—Partial reversal under the blue, but full reversal under the uncovered part. In this experiment the print out image appeared as strong under the blue as under the uncovered part, yet, on development, a full reversal only occurred where uncovered. It is well to note here that a similar print-out image under red tissue reverses perfectly. It will be noticed in this experiment the advantage gained by increasing the power of the light, compared with Experiments 11 and 12. Experiment 14. —As Experiment 13, except that a green tissue was used to part cover the plate and the magnesium burnt at 8 in. This experiment shows the result of reversal on the front surface and non-reversal on back surface of film very distinctly; the effect only took place on the uncovered portion of plate, the tissue covered part being insufficiently exposed. Experiment 13 shows, had the magnesium been burnt 2 in. nearer, a full reversal would have occurred. It is interesting that this plate has caught the transition stage nicely, as the result would disappear on fixing. The plate was not placed in hypo. Experiment 15.—No preliminary exposure and no coloured tissue. Exposed to 12 in. of magnesium at 4 in. Result.—Very good reversal. Experiment 16.—As Experiment 15, but preliminary exposed for thirty seconds to candle-light at 6 in. Result.—Reversal as in Experiment 15. Experiment 17.—No preliminary exposure, then exposed to 18 in. magnesium but at 4 in. Result.—Very good reversal. Note.—Experiments 15, 16, and 17 show the improve ment in results by stronger exposure. Experiment 18.—Edwards’ slow isochromatic plate. No preliminary exposure; no coloured tissue. Exposed to 12 in. of magnesium at 4 in. Result. —Good reversal. Experiment 19.—Edwards’ transparency plate. No pre liminary exposure. Exposed to 12 in. of magnesium at 4 in. Result.—Very weak reversal. Note.—Edwards’ landscape plates, exposed to from 12 to 18 in. of magnesium weighing 4 gr. to the foot, and burnt at 4 in. distance, produces the best results, no pre liminary exposure being required, sufficient fog being produced to develop to full density where the plate is protected, and at the same time the oxidising rays do their work on the unprotected parts. Experiment 20.—Strips of red, blue, and green tissue were cut and laid on a negative so as to divide it into four sections, one of which was uncovered. No preliminary exposure being made, a landscape plate was exposed in contact with the sectional negative for five minutes to direct sunlight. Result.—Under the blue and uncovered sections a very strong print-out positive appeared, and under the red and green a delicate print-out positive. The blue and un covered sections developed decidedly positive, which gradually fogged away and left very thin reversals, mere ghosts. The red and green sections developed strong and vigorous reversals in a very decided manner, without any strengthening of the print-out positive. The develop ment was the same as met in every-day procedure, but under the blue and uncovered sections there was an increase of strength in the print-out image, then a gradual fog, and finally a thin reversal. The green section is slightly more dense in deposit than the red. Experiment 21. —Preliminary exposed plate one minute to candle-light at 6 in., then proceeded as in Experiment 20. Result. — As in Experiment 20, but rather more deposit under the blue and uncovered sections, and more general fog. These experiments, I think, tend to show that a reduction is to some extent requisite in order that a sub sequent oxidisation may occur, but that a total reduction is not desirable, and that this reduction may be obtained either by a preliminary exposure, or by the concurrent action of the reducing and oxidising rays in one exposure ; in the latter case, the oxidising rays require so much time for their work that the reducing rays have ample time to exert their influence on even the most protected portions of the plate ; evidently the best conditions being those under which a full-timed exposure or fog is made to balance a full effect of the oxidising rays, so that, when the latter produce as nearly as possible clear glass, the former may develop to full density.—Journal of the Camera Club. ROYAL CORNWALL POLYTECHNIC EXHIBI TION: PHOTOGRAPHIC DEPARTMENT. Completion of Awards. Messrs. Taylor, Taylor, and Hobson, of Leicester, send a pair of nine-inch lantern objectives, which the judges put to a practical test, and Mr. Brooks used them at his lantern entertainment; their performance left nothing to be desired, and the judges have awarded them a first silver medal. Mr. IL R. Beard exhibits a pair of his gas governors, with special packing to prevent straining and bursting of the pressure gauge, which seems to be very efficient; to these have been awarded a first bronze medal. He also sends a carrier for dissolving effects with a single lantern, which is a very clever arrangement, and is highly commended. The same exhibitor shows a compact little optical lantern, which packs into a very small compass, and will recommend itself to those who admire portability. Mr. C. A. RUDOWSKY writes that as the price of platinum is lower, the manufacturers of the Pizzighelli paper, Dr. Adolf Hesekiel and Co., Berlin, have reduced their prices 25 per cent. Carl Suck.—The Photographisches Wochenblatt of the 3rd inst. appears with two black-bordered pages in memory of Carl Suck, who died on September 2nd, after protracted illness, at the age of fifty-eight. The deceased, though engaged in business-management, devoted much time to original research, to the advantage of photograghy. The Zusammenkunft Prak- tischer Photographen Berlins pays its tribute in the record that they have lost a beloved colleague, a true friend, and a zealous promoter of the art.