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The photographic news
- Bandzählung
- 24.1880
- Erscheinungsdatum
- 1880
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- Englisch
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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. 1127, April 9, 1880
- Digitalisat
- SLUB Dresden
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Zeitschrift
The photographic news
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Band
Band 24.1880
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- Register Index 631
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Band
Band 24.1880
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THE PHOTOGRAPHIC NEWS. Proceeding in this way, it was easy to arrange the cards in order of purity, and find out at once those best fitted for use in the mounting room. Out of the seven cards examined, No. 1 proved to be the worst of the series, for in this case the pure white tint was evidently got by the employment of highly-bleached paper-stuff, whereas the enamelled card, No. 2, owed its whiteness to the fact of a thin, uniform coat of sulphate of baryta being applied to the face of the mount, the substratum being of inferior colour, and probably never bleached in the pulp state. At all events, this card contained a mere trace, if any, of hyposulphite, the quantity of iodo dextrine solution required to impart a permanent tint being only four measures, against three required for pure water ; whereas the cheap white card, No. 1, took as much as thirteen measures to communicate a permanent tint to the solution. All the rest took three and four measures respectively, including the brown card, which cannot, therefore, be condemned as containing hyposulphite. Upon taking the layers apart, after soaking in water, I found here, also, the substratum to be quite satisfactory ; probably never bleached with chlorine, and consequently not requiring an antichlore. I then examined the yellow colouring matter, which is laid on back and front of the card in the form of a thick coating worked to a highly-glazed surface. The pigment cannot well be scraped off, nor is it soluble in warm alcohol. Immersed in water it soon drops off the card as a heavy ochrey deposit, and this was carefully examined. I find it to be a mixture of sulphate of baryta and basic sulphate of peroxide of iron, and the prejudicial action upon the photograph, if really exerted, must be due to the last-named substance, which, it will be remem bered, is the ochrey deposit that forms in solutions of sulphate of iron exposed to the air. I have no knowledge of any experiments showing the action of this body upon silverprints, and cannot predict what will be the effect of long contact. This point, if not already ascertained, is well worth investigation. Mention is made by Mr. Marshall Wane of bis having a stock of some two thousand cabinet mounts “ hidden away in the dim regions of a Manx attic," which he never intends to use. Without mentioning names, I know of two or three other eminent photographers who, at various times, have met with similar experiences, and it was upon the representation of one of these gentlemen that I first took up the subject, and condemned a lot of yellow mounting cards in the year 1868. Ultramarine—a sulphur compound—is another pigment which should never be allowed to become mixed in the pulp from which mounting boards or cards for photo graphic use are intended to be made. Its detection is ex tremely easy, for one has only to burn the cards, and look for the blue particles in the residual ash. It is never destroyed by burning, being itself the product of a furnace operation. Large quantities of ultramarine are known to be employed in the manufacture of blue-wove papers, and in some kinds of cardboard. Of course, it will be under stood that this objection applies only to such as arc intended for the mounting of silver prints, for in the case of carbon prints and platinotypcs no fear of injury from this source need be entertained. The use of the copper, zinc, and tin alloys known as “ gold and silver bronzes,” for embellishing photographic mounts, has already been shown to be very prejudicial. I have frequently seen photographs peppered all over with spots of decomposition, attributable to this cause; and, inasmuch as these metallic particles are often very loosely adherent, it is not wise even to use the bronzes for printing the name and address on the back of the mounting cards, as was formerly a frequent practice. The lopic for next week will be “The Chemistry of the Gelatine Process,” by Dr. H. W. Vogel, of Berlin. THE PREPARATION OF GELATINE EMULSION WITH AMMONIA. Herr E. von Schlicht, an amateur of Berlin, has been trying the addition of ammonia to gelatine emulsion, as re commended by Van Monckhoven, and gives in the Photo- yraphische Mitlheilungen an account of his experiments, of which we append a short abstract. He used the formula for the emulsion which Professor Vogel has published, viz.:—1 gramme of white German gelatine ; 1 gramme of dry ammonium bromide, dissolved in 20 grammes distilled water ; 1-7 grammes of crystallized silver nitrate, dissolved in 10 grammes distilled water. To this he added precisely the quantity of ammonia prescribed by Van Monckhoven ; but as this quantity must depend on the strength of the solution, he first determined the specific gravity of the latter. Adopting this method it was found necessary to take 1'5 grammes of ammonia solution of '963 specific gravity. The mixture was kept warm for twenty-four hours, and then, as no constant water supply was at hand, it was washed in alcohol. When fresh alcohol had been three times poured over the mixture, all the soluble salts were drawn out of it, together with the water. He had prepared double the quantity of emulsion given in the above for mula, and after pouring off the last drop of alcohol, the mass weighed 25-4 grammes, showing that it still retained 18 grammes of alcohol. It was then dissolved in 56 grammes of water, and the plates were coated in the usual way; in consequence of the emulsion containing so large a propor tion of alcohol, the plates, after standing in the drying-box on a warm stove for twelve hours, became perfectly dry. The plates proved to be about one-third more sensitive than those coated with emulsion which contained no ammonia, and which had been kept warm for five days; their intensity was exactly the same as that of emulsion plates without ammonia. Most peculiar was the green tint very perceptible in the depth of these plates, when viewed by reflected light against a dark background—a phenomenon which is not observable in plates prepared without ammonia. The greatest difference, however, between these plates prepared by the new method, and the old ones bought from the manufacturers, consists in the ease with which they can be softened preparatory to using the developer. The former, Herr Von Schlicht was compelled to leave to soak for a considerable time in spring water ; the latter were softened in the short space of time required for mix ing the developer. Reasoning on this peculiarity, Herr Von Schlicht believes that he has found the cause of the special action of the ammonia. He attributes it to the diffusive action of the ammonia on the gelatine, enabling the developer to penetrate with greater ease. This diffu sion was probably effected under the old system by the lengthened emulsification. A contrary effect may be obtained by treating the film with alum before develop ing, that is, by rendering it denser ; in this case the image only appears after long-continued development, and can be seen on the surface by reflected light. AN IMPROVED METHOD OF ALKALINE DEVE LOPMENT FOR GELATINE PLATES. BY B. J. EDWARDS.* NorWITIISTANDING all that has been written from time to time on the subject of alkaline development, I make no apology for again introducing the subject to your notice this evening in connection with gelatine plates, the latest and most important improvement in photography. Deve lopment by alkaline pyrogallic has always been a favourite method of working, owing to the great latitude in exposure allowed by its use, and to the fact that it affords almost • Read before the South London Photographic Society.
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