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

After development, one-half of the plate will show on. ... 250 grammes Water Sugar Gum-arabic Bichromate of ammonia Water... Zinc filings Sulphuric acid After this has dissolved, the solution is again kept for some days in a well-stoppered bottle. Solution B. bottle. Then are added : — Sodium sulphite PHOTOGRAPHY IN GERMANY. BY HERMANN E. GUNTHER. Photo-Engraving IN HALF-TONES—Measuring the Speed of Drop-Shutters—A New Accelerator. Photo-Engraving in Half-Tones.—Herr E. Ammann des cribes, in the Phot. Archiv, a process of making grained negatives, by which an ordinary negative may be employed and converted directly into a grained one. It is only necessary that the negative be clear and without signs of fog, and that it show sufficient density, negatives of such qualities only being suited for the process in question. The negative, which should not be varnished, is coated with a four per cent, solution of plain collodion, to which a few drops of castor oil have been added, when it is placed aside to dry. After the negative has dried, it is coated with the well-known solution of gum-arabic and bichromate, as generally used in the dusting-on process. In my own experiments with this process the following formula answered well:— an uniform darkening of its film, the other half, however, six strips of successively increasing darkness. It must then be stated at what point between the instantaneously exposed strips the darkening of the film corresponds to that of the timely exposed half, when it will be possible to estimate even by one-tenth. The source of light must, of course, be a constant one during the whole series of exposures. A Neto Accelerator.—Pot some years, a solution under the name of “ Excelsior ” has been sold in Germany, which was recommended by its inventor, Captain E. Himly, as an accelerator in ferrous oxalate development, as well as in pyro development, and which, at the same time, was said to prevent the lights from becoming hard in developing, and to bring out more detail in the light tones of the nega tive. As far as I am aware, the addition of this composi tion has answered well in the hands of those operators who have used it. I am glad to see that Captain Himly has now published the formula of his new accelerator, and, according to the Photo. Archiv, it consists in the following. Two solutions are made :— Solution A. measurement of the action by photographing with the shutter a glaring point in rapid motion, the speed of which is known ; the other consists in the direct measurement of the speed of the shutter, generally by using a vibrating tuning-fork registering a curve on the blackened shutter during its passage. A simpler and much more certain method, which requires no specially constructed appa ratus, has been published recently by Professor Leonhard Weber in the Phot. Mittheilungen. It consists in the following. One-half of a dry plate is exposed exactly one second to an uniformly lighted shining surface, with a given stop and a given lens. Then the other half of the dry plate is exposed to the same surface by means of the shutter, strip by strip, the time of exposure in each case being slightly prolonged, the arrangement of the camera being, however, the same as before. After deve lopment of the plate, it must be ascertained which of the various strips of the one half—in other words, what num ber of instantaneous exposures—shows the same density This solution must be well filtered, and not kept for too long a time. After coating, the layer is allowed to dry at a temperature of from 1229 to 140“ F. After about ten minutes it will dry with a high gloss, and whilst still warm the plate is exposed beneath a glass screen with pure black lines and clear transparent spaces in an ordinary printing frame in direct sunlight. One minute will be sufficient for exposure in most cases. The plate is then developed by means of a large, soft dust-brush, and with very finely-prepared plumbago. When the grain has attained the required depth, it is necessary to wash the negative thoroughly in order to remove the bichromate from its film, since otherwise spots would be produced in drying. This elimination is best done by means of a solution of 2 parts of caustic potash in 100 parts of water, in which the negative is allowed to remain until the yellowness has entirely disappeared. The grain printed-in in this manner on the negative adheres tightly to it, after which the negative simply requires to be varnished. Measuring the Speed of Drop-Shutters.—The various methods of measuring the speed of drop-shutter exposures ■which have been suggested from time to time may be divided into two classes. The one consists in the direct 100 c.c. 10 grammes 10 „ 4 to 5 ,, as the first half of the plate, which was exposed for one second. I o effect this experiment an ordinary dark slide may be used, arranged as follows. A thin but opaque cardboard is cut up so that it fills up exactly the space of the dark slide destined for the dry plate. A longitudinal incision is then made exactly through the centre of the cardboard down to about one centimetre distance from the lower edge of the cardboard, and from this point a right-angled incision sideways to the lateral edge of the cardboard. The piece included by the incisions is then cut off, so that one-half of the plate is laid open. After this half of the plate has been exposed the cardboard is turned over, leaving open the previously covered half of the plate ; the cover of the dark slide is then withdrawn for about one-sixth, and the drop-shutter released ten times successively ; then the cover is again withdrawn for one-sixth, and the shutter released again ten times, and so 500 c.c. 100 grammes 50 drops Sulphurous acid is formed by the above. The solution is well shaken, and kept for some days in a well-stoppered Water... ... ... ... ... 500 c.c. Sulphite or sulphate of ammonia ... 250 grammes The solution is filtered, and solution A mixed by equal parts with solution B. This mixture forms the stock solution. If it is intended to use it in combination with the pyro developer, it is necessary to add 1 gramme of sulphocyanide of ammonia to each 50 c.c. of the stock solution. If it is, however, intended to use it as an addition to the ferrous oxalate developer, 4 grammes of citrate of iron and ammonium should be added to each 50 c.c. of the stock solution. The solutions must be all well filtered. For developing with pyro, the “Excelsior” solution should always form 2} per cent, of the whole quantity of the developing fluid; in developing with ferrous oxalate, however, it should amount to 5 per cent, of the whole