The photographic news

• Bandzählung: 7.1863
• Erscheinungsdatum: 1863
• 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-id1780948042-186300004
• PURL: http://digital.slub-dresden.de/id1780948042-18630000
• OAI: oai:de:slub-dresden:db:id-1780948042-18630000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

downwards. It is then laid on a porcelain slab, and the surface rubbed gently with a soft sponge dipped in gum water. This will remove the unaltered gelatine, and, if all the other operations have been rightly performed, a perfect positive image in printer’s ink remains. This, when dry, is ready for transferring to zinc or stone. The zinc plate is, of course, prepared to receive the transfer; this is effected by first smoothing it, and then giving it a grain by moans of fine sand and muller. The surface so produced has an affinity for the greasy ink some what similar to that of the lithographic stone. To effect the transfer the print is placed for a minute or two between two sheets of damp paper, and then laid on the prepared zinc plate, and passed through the lithographic press. This done the print is moistened on the back, which causes the ink to leave it the more readily. On removing the transfer paper, the image is left in the transfer ink on the zinc plate. It is now etched, as the next process is termed, by means of a mixture of gum-water, phosphoric acid, and a decoction of galls. Four ounces of Aleppo galls are steeped in three quarts of water for a day, and then boiled. One quart of this is added to three quarts of gum-water about the con sistency of cream, and three ounces of a solution of phosphoric acid. To prepare the latter, some sticks of phosphorous are placed in a pint bottle, not quite full of water; a hole is made through the cork to admit air; this acting on the phosphorous, which projects above the water, produces oxidization, and the water dissolves the phosphoric acid as soon as it is formed, and in a few days produces a solution strong enough for use. The etching liquid is poured on the plate, and allowed to remain from twenty seconds to a minute, fine work requiring a shorter time than coarse work. The plate is then washed with water, and dried. The transfer ink is next removed from the plate with tur pentine, or with a mixture of turpentine, olive oil and gum water. It is then rolled up with printing ink, and is then ready for use. In the process which Col. James has termed Photopapyro- graphy, the image obtained in greasy ink, on paper prepared with gelatine and bichromate, instead of being transferred to zinc or stone, is used to produce one or more positive im pressions on paper, by passing it through the lithographic press. The negative should be in such cases reversed, either by being taken through the glass plate, or by means of a reversing mirror or prism. • For the reproduction of manuscripts, printed matter, &c., theuseof negatives obtained, by wet collodion on paper instead of glass is recommended. The sensitiveness is stated to be superior to that of wet collodion on glass ; and when waxed it yields excellent results. With such negatives the image need not be reversed for photopapyrography, as there will be but an inconsiderable loss of sharpness in printing through the paper. The volume contains an interesting account of the rise and progress of the application of photography to this branch of the public service, and of the discovery of photo zincography. It is unnecessary to revive any discussion on the subject here. Different steps in the discovery were probably due to different individuals in the establishment, who have, from time to time, received due acknowledgment. The general control, the suggestion, direction, or permission, have rested with Colonel James, and photozincography very naturally receives public recognition as his process. Since the publication of this book, Colonel James, as our readers know, has devoted some attention to the production of half-tone, an accident having suggested the means, in a certain condition of the prepared paper, produced by keeping it a few days before use. The several specimens, with which Colonel James has favoured us of the results, have been full of promise. There is unquestionably abundance of half-tone, the fault at present existing being rather a want of deep blacks for the shadows, or a want, perhaps, of perfect gradation generally. Sufficient is, however, already produced to indicate the possibility of obtaining photolithographs with proper gradation of half-tone, pure lights, and deep shadows. This possibility has frequently been, doubted, on the ground that gradation in litho graphy could only be obtained by artificial or conventional means. We find enough done to convince us that more may be done, and we have pleasure in learning that Colonel James is prosecuting his experiments in this direction. We have before stated, that by far the best photolitho graphs we have seen, as regards gradation of tone, are some done by Asset’s process. In these, instead of gelatine or al bumen, a paste of wheaten flour is used with the bichromate. The precise condition of the organic matter in combination with the bichromate, seems materially to affect the question of half-tone, and suggests a direction for experiment. A specimen we received from Col. James, produced by the bitumen process, which has recently been vaunted as giving half-tone, was alamentable illustration of the worthlessness of that method, as the print is almost entirely destitute of any qualities which could give it value, and strikingly enforces the fact, that the process is entirely superseded by the method of transferring now in successful use. PHOTOGRAPHIC CHEMICALS: Their Manufacture, Adulteration, and Analysis. Alumina Salts.—The salts of alumina are only of indirect interest to the photographer; we shall, therefore, give but a brief sketch of their history. The earth itself is a white powder, tasteless and inodorous, and after ignition insoluble in most acids., It may readily be prepared in the hydrated state, by adding an excess of ammonia to hydrochlorate or nitrate of alumina, and thoroughly washing and drying the gelatinous precipitate. If alum is used, the resulting hy drate is contaminated with sulphuric acid. Alumina has less affinity for acids than any of the bases we have yet mentioned, and forms with them compounds which have little stability. They are decomposed sometimes by simple ebullition, and deposit hydrate of alumina. When the earth is precipitated, either in this manner or by the addition of an alkali, it has a remarkable tendency to carry down with it organic, and especially colouring matter, which may be in solution ; many kinds of inorganic impurity, com monly classed under the generic term mud, or dirt, are also carried down and removed from solutions in this way. This property of alumina is applied to great use in the arts and manufactures. The colour-maker utilizes it in the prepara tion of lakes, by precipitating alumina in the presence of some brilliant organic dye; and it is frequently used also for the purpose of decolourising solutions. Recently precipitated alumina has a similar property. When put into a liquid containing organic colouring matter, it almost invariably attracts this to itself, becoming tinted with the particular colour, whilst the solution is rendered almost colourless. The dyer and calico printer avail themselves largely of this property. When cotton goods are placed in a solution of a colouring matter, they refuse to fix the substance, and do not take the colour in the same way as silk or woollen goods would. The manufacturer, therefore, employs the artifice of precipitating aluminum into the cotton fabric before im mersing it in the colouring solution. Upon now dipping it into the coloured bath, the alumina, acting as a mordant, causes the goods to take the dye readily. Chloride of Aluminium.—This salt has recently become of considerable commercial importance, being the starting point in the preparations of the metal aluminium. It is, like many other chemical compounds, very difficult and tedious to make on a small scale, although attended with no difficulty when prepared as a manufacturing operation. When alumina is dissolved in hydrochloric acid, it may be assumed that the solution contains chloride of aluminium ; but upon evaporating the liquid to obtain this body in the solid state, a residue is left containing chloride of aluminium with the elements of water; and upon further increasing the