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

March 27, 1891.] THE PHOTOGRAPHIC NEWS. 239 be most carefully examined, so as to save disappoint ment, for prevention is better than cure, especially in the case of damaged negatives, where cure is next to impossible. But it is not alone the portable photographic appara tus that must be looked to at the beginning of a fresh season ; the dark room and its appurtenances must also be overhauled. The most important feature to deal with first is the light-filtering medium, whatever it may consist of. All ruby media, whether of cloth or paper, are liable to change, especially if they have been exposed for any time to the action of daylight. We have seen specimens so situated that have, in a few months, changed from a rich and absolutely safe red to a washed-out pink that would hardly be a protection to a’plate prepared from comparatively insensitive silver chloride. Even glass is not safe, but is liable to change, although the bleaching action here is not nearly so marked as in the case of paper or cloth. The medium protecting a lamp is not liable to such rapid deterioration, for it is not usually exposed to that energetic bleaching agent which we have in sunlight; but still the lamp should be looked to. One more word. At the beginning of a new season, clear the decks for action by eliminating from the dark room everything that is not absolutely wanted for work. Dismiss the empty bottles, pour away solutions of uncertain composition, make good all labels, clear away cobwebs and dust, and your work will be all the better for the trouble incurred. ELECTRO-CHEMICAL REVERSALS WITH THIO CARBAMIDES. BY COLONEL J. WATERHOUSE, B.S.C., ASSISTANT SURVEYOR GENERAL OF INDIA. Farther observations made with silver plates coated with a film of precipitated silver bromide in pairs of one exposed and one unexposed plate, connected with a very delicate suspension galvanometer, showed not only a distinct electric current between the plates immersed in the plain eikonogen-lithia developer, but a reversal of the current with plates immersed in some of the same deve loper to which five drops per ounce of the compound salt of thio-carbamide and ammonium-bromide had been added. With the ordinary developer, the exposed plate forms the negative pole of the circuit, whereas with the thio carbamide developer it forms the positive pole. The same rule has been found to hold good with thio-sinamine. With the thio-carbamide developers the current is more powerful than with the plain developers. Farther experi ment is, however, necessary with other plates to confirm this reversal of the current, which seems highly probable, and was to have been expected. Blue Pbints on ArBUMENISED Paper.—Sensitise the paper with the following solution :— Citrate of iron and ammonium ... 34 drachms Water ... ... ... ... ... 3 ounces Red prussiate of potash 2} drachms Water ... ... ... ... ... 2 ounces Mix equal parts (at the time of using), and float the paper for about half a minute, then dry. The prints may be mounted and burnished. The sensitised paper does not keep. —Scientific American, PHOTOGRAPHY IN GERMANY. BY HERMANN E. GUNTHER. Colouring Silver Prints—Diapositives from Engravings and Prints—Printing on Wood—Combined Pyro and Hydroquinone Developer—Turpentine as an Accele rator. A Novel Method of Colouring Silver Prints.—Dr. Miethe reports on a new method of colouring albumen prints, suggested by Ogonowski in his book on photochromy. It consists in the following. Ordinary salted paper is floated on a silver bath, printed rather weakly beneath the negative, washed out, toned and fixed as usually. The weak print thus obtained is placed, whilst still moist, on a sheet of wet blotting-paper, and together with it on a glass plate. The print, which by this procedure is kept moist, is then coloured with water-colours, only natural colours being, however, applied,and white body-colour; vermilion, chrome, and cadmium yellow are avoided. The whole is then allowed to dry, and the print floated from once to three times on a solution of salted beaten albumen, when it is again sensitised, and placed in the right position beneath the negative in the printing frame. It should now be printed as usually on albumen paper, then toned and fixed. The colours, which are prevented from coming off by the albumen film, are perfectly preserved, and the pictures obtained by this method are said to give splendid effects. How to Make Diapositives from Engravings and Prints in the Original Size. —The following simple and trustworthy method is described by E. Ammann in the Archiv. A well-polished plass plate is coated with one of the well- known sensitive gum and bichromate solutions, as used in the powder process, and dried. The copper engraving or the wood-cut from which the transparency is to be taken, is placed with its back outwards in the printing-frame, the prepared glass plate being laid on it. It is then exposed, dusted-in with suitable colours, washed out, dried, and varnished. The transparency is then finished. In order to prevent the paper of the engraving from adhering to the bichromate film of the plate during printing, the back of the engraving or print is previously rubbed in with turpentine, and then laid aside for a few minutes. The paper is thus not only provided with fatty matter which prevents adherence to the glass, but it is at the same time rendered transparent, so that in dusting on the colours the grain of the paper remains invisible. If pure and clear turpentine is used, no trace of it will remain on the paper after evaporation. Printing on Wood.—A professional photographer who does a great deal in making prints from negatives on sensitised wood blocks for the use of wood-cutters, was kind enough to demonstrate to me the other day his mode of working. It will, perhaps, be of interest to some of your readers:— Gelatine ... ... ... ... 8 grammes White soap ... ... ... ... 8 „ Water ... 500 „ The gelatine is allowed to swell, dissolved by means of a hot water bath, and the soap added gradually with constant stirring. Finally, the solution is filtered through muslin. With this mixture, to which some zinc white is added, the wood block is well rubbed in, and allowed to dry ; the film should be as thin and even as possible. The wood block