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The photographic news
- Bandzählung
- 35.1891
- Erscheinungsdatum
- 1891
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1716, July 24, 1891
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The photographic news
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unusually powerful contrasts, the lights of the positive image turning out perfectly white, whilst the shadows— if only two tones are taken into consideration—have acquired double the depth or intensity in relation to the lights. Paramidophenol Developer. — This new developer, introduced by Messrs. Lumiere, has now been tried also by our German authorities, and their judgments are, on the whole, favourable to this reducing agent. Professor Vogel finds that the pure paramidophenol is very in soluble, so that it was impossible to prepare with it the solution recommended by Messrs. Lumiere. Dr. Schu- chardt, of Gbrlitz, has, however, succeeded in producing an hydrochloric preparation of this substance which, in the hands of Prof. Vogel, proved to be more soluble than the first one, though it is said to dissolve much less readily in cold water than hydroquinone. It is, therefore, neces sary to heat the water previously. The developer thus obtained is very energetic, giving, however, somewhat thin negatives, and the mixed solution soon becomes brown. If the paramidophenol solution and the sodium sulphite solution are kept separately, they will keep clear. Also Prof. Eder and E. Valenta state that the paramidophenol forms an excellent developer, giving, according to its com position, every degree of softness or intensity. The colour of the negatives is greyish-black, the film being free of every bluish or greenish colour, even if a neutral fixing bath is used. The authors recommend the use of a dilute solution, for the reason that then the paramidophenol does not crystallise out of its solution, and the developer becomes less expensive. Moreover, the diluted solu tions form equally excellent developers as the concentrated ones. The formula; recommended by the authors are the following: — Paramidophenol-Soda Developer. Water... ... ... ... ... 1,000 c.c. Sodium sulphite ... ... ... 80 grammes Carbonate of soda ... ... ... 40 ,, Paramidophenol ... ... ... 4 , Paramidophenol-Potash Developer. Water... ... ... ... ... 1,000 c.c. Sodium sulphite ... ... ... 120 grammes Carbonate of potash ... ... ... 40 ,, Paramidophenol ... ... ... 4 ,, The latter is specially well suited for plates which tend to give thin negatives, whilst the soda developer yields more delicate images. With the latter, also, transparencies on gelatino-bromide emulsion may be developed very suc cessfully. Chloro-Cyanin as a Red Sensitiser.—Cyanin, which has been introduced in photographic practice by V. Schumann, forms, besides chlorophyl, the best sensitiser for red and orange. Professor Eder, in the Photogr. Correspondenz, points out that all commercial cyanin is the so-called iodo-cyanin, by the use of which fog is produced sometimes during developing. He recommends, therefore, to convert the iodo-cyanin into the analogous chloro-cyanin, which latter is said to show less tendency to the formation of fog. This conversion may be easily effected in the following manner: —The cyanin is powdered, placed in a porcelain or platinum dish, and some water and hydrochloric acid poured over it. It is then evapo rated in a water-bath (with constant stirring) to dryness, the residuum being again wetted with hydrochloric acid, and then once more evaporated in the water-bath. There remains behind, with evolution of hydric iodide, a residuum of chloro-cyanin, which still contains traces of hydrochloric acid, and is not, therefore, entirely blue. The last traces of hydrochloric acid will, however, escape by heating the dish carefully on a sand-bath until the edge’s of the film of cyanin become dark. If the dish has been previously weighed, the increased weight will give the amount of chloro-cyanin which it contains after evaporation, which may be dissolved in a corresponding quantity of alcohol. RECENT DEVELOPMENTS IN PRINTING PROCESSES* BY C. H. BOTHAMLEY, F.C.S. The permanence of the kallitype images is of considerable interest. The black images by both the first and second method are not altered by exposure for forty-eight hours to the products of the combustion of sulphur in air, nor by immersion in a solution of sulphurous acid for the same length of time. A solution of sulphuretted hydrogen, if dilute, changes the colour to bluish black, but produces no other alteration ; if the solution is strong, the bluish black image undergoes a further change, and becomes brown. A dilute solution of ammonium sulphide changes the colour to brown, with no loss of detail and not much loss of intensity; the brown colour thus produced is very suitable to certain subjects. The sepia paper, likewise, seems unaffected by the pro ducts of the combustion of sulphur; sulphuretted hydrogen or ammonium sulphide first changes the sepia image to black, but it afterwards becomes gradually brown. No prolonged experiments on the behaviour of mounted prints have as yet been possible, but there is no reason to doubt that, under ordinary conditions, kallitype prints are permanent. It is, of course, not to be expected that kallitype can as yet equal platinotype, but it is by no means improbable that in time the difference will be chiefly a possible difference in permanency. The process is already capable of giving very good results, and it is considerably cheaper than platinotype. The other processes that I shall describe belong to an entirely different class; they are the first practicable photographic processes based on the use of coal-tar colours. Both processes depend on the formation of azo colouring matters from diazo compounds, and they may be spoken of as diazotype, but they differ in the nature of the change that the light produces, and in the condition under which the colouring matter is formed. Diazo compounds are a class of compounds characterised by their power of uniting with carbolic acid or any other phenol, any naphthol, or any amine to form an azo colouring matter, the tint of which depends on the nature of the diazo compound, and also on the composition of the particular phenol, naphthol, or amine. Yellow, orange, brown, purple, scarlet, and blue may be cited as examples of the variety of colour that can be obtained in this way. Feer-type is the first of these processes, and is so called from the inventor, Dr. Adolph Feer (German patent 53,455, December 5th, 1889). It is based on the fact that diazo compounds in contact with acid sulphites form diazo-sulphonic compounds, and these form no colouring matter. If, therefore, a diazo-sulphonic compound is mixed with an equivalent quantity of a phenol or an amine, no colouring matter is formed. If, however, the mixture is exposed to light the diazo-sulphonic compound is decomposed, the diazo compound is set free, and, since a phenol or amine is already present, a colouring matter is formed as fast as the diazo compound is liberated. * Concluded from page 517.
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