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The photographic news
- Bandzählung
- 27.1883
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- 1883
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- Hochschule für Grafik und Buchkunst Leipzig
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- No. 1289, May 18, 1883
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- Titelblatt Titelblatt I
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316 THE PHOTOGRAPHIC NEWS. [Mat 18, 1883. Mix the arrowroot and a small quantity of the water to the consistency of cream, then add the remainder of the water and the gelatine a little at a time; boil on a water bath for five minutes, stirring the whole time, and allow to cool; before quite cold, add the spirit and carbolic acid. This mixture will keep a long time if well corked. Another:— Dextrine ... ... 1 ounce Water 1 „ Methylated spirit 2 ounces Mix the spirit and water, stir in the dry dextrine, until a smooth paste is obtained; heat on a water bath until a clear brown solution results. RELATIVE ACTION OF CARBONATES AND AMMONIAS WITH PYROGALLOL DEVELOPERS. BY LYDDELL SAWYER.* UP to the present time, with one or two exceptions, ammonia seems to be the only accelerator accepted to act in conjunction with pyrogallol for the reduction of images formed on gelatino- bromide of silver films, though I am somewhat at a loss to understand why this alkali should have had the almost sole preference for so long a period. I may state that, after about a month’s practical every-day working, using disodic carbonate side by side with ammonia, I find two advantages in working the former, which appear to me to be of great importance—namely (1), increased rapidity of exposure; and (2) more force in the minor lights and general middle grade of the image, where unquestionably the weakness of bromide of silver lies, when distinguished from collodio-iodide films. With regard to reduction of exposures, if the action of the alkali ceased when it had rendered the pyrogallol alkaline, then we might be right in supposing the work of each accelerator as equal; but it is found that these substances do further chemical work. Another cause of the increased energy, which may be con sidered as beyond conjecture, is that carbonate of soda may be used without any restrainer, yet it being of sufficient strength to give full density to the image without fogging. I believe that the extra strength of middle gradation produced with carbonate is due to physical causes, this developer appear ing to give brighter pictures by producing the image more directly on the surface of the film, instead of being imbedded so far into the gelatine, and some of the more tender details depreci ating in power from lateral and angular placement. Most of the images which I have developed, while possessing sufficient density, have yet in their unfixed state shown little or nothing from the back of the plate ; what small amount was visible being sometimes of actually a positive character, through the unaltered bromide film, forming the shadows, being tinged darker with the absorbed oxide stain; while the reduced portions, representing the top lights, had resisted the stain more, and thus appeared white from the back. The fact of the deposit being comparatively on the surface of the film would suggest the possibility of using thinner coatings of emulsion, although that is a project which I have little sym pathy with, my impression being that our negatives are greatly impoverished by the present thinnesss of commercial films. I have noticed that when using the carbonate accelerator, the image seems to develop all its details first, and their intensity to gradually accumulate afterwards. When contrasted with the ammonia treatment, this effect is very noticeable, and it must be more advantageous in bringing up the minor lights in their true relationship than with ammonia. It has some appearance, too, suggestive of the intensity being gained rather from the solution than the film, as though some of the silver bromide was dissolved, and then deposited by the power of crystalline attraction, as in the collodion wet process. There seems to be total immunity from green fog with the use of the carbonate developer, even when in its most concen trated form ; although grey fog, due to the metallic reduction of the silver throughout the film, may be readily produced, in strong solutions especially, when the carbonate is in proportion ate excess to the pyrogallol. I find disodic carbonate to be soluble in about its own weight • Read before the Newcastle-on-T'yne and Northern Counties’ Photo- graphic Association. of boiling water, and in about twice its weight of cold water, using fluid measurement for the water. This latter combination is equal to fifty per cent, of soda, and I have found it possible to develop images with this actual saturated strength; a matter which appears surprising to me when it is remembered that very little more than one per cent, of ammonia can be ordinarily used, and even that has to be restrained with bromide. The new quarter plates here shown are developed with this excessively strong, unrestrained mixture, and, while they are palpably fogged, yet it may be acknowledged that their printing qualities are surprisingly good. I have obtained negatives quite free from fog with 1 to 4, or twenty-five per cent, carbonate solution ; while again in other cases, I have found films heavily veiled with this same strength. Indeed, there are some fluctuating influences connected with the process that I am not in a position so far to account for. As, for instance, in the yellow discolouration of the film from oxide staining, I have found the resulting image in one case perfectly clear from those effects, and in the next plate, with the same strength and conditions of the developing solution, this film has been sufficiently impregnated with the discolouration to form a positive image on the back of the plate, as I before mentioned. Then, when the stain has been removed after fixing, as it can be with the ordinary alum or acid treatment, the discolouration has again occurred, in a lighter form, even during the subsequent washing necessary to remove the decolourizing agent. I suspect that the different thicknesses of the gelatine films have much to do with the cause of this variation, the thinner films encourag ing the staining effects. I can discover very little difference of rapidity between 1 to 4 and 1 to 10 strength of carbonate in solution; while with the latter proportion immunity from fog is easily obtained under reasonable circumstances. All things considered, I have little hesitation in recommending the following formula for simplicity, efficiency, and cheapness Make a saturated solution of ordinary washing soda by simply throwing an excess of the crystals into a jar of hot water, and stirring well ; when cold, this will yield a stock solution in the proportion of two of water to one of soda. For developing, use— Saturated solution of carbonate of soda ... 1 part Water 5 parts And to each ounce of this diluted solution add 20 minims of a ten per cent, alcoholic solution of pyrogallol, immediately before using. This gives disodic carbonate forty grains, and pyrogallol two grains, to the ounce. By the way, I cannot too thoroughly express the advantage I think there is in quoting formula whenever possible, as in the proportion of the substance in question to the ounce of the vehicle or solvent, or else to quote it as so much per cent. It is so comprehensive, the proportion is so easily grasped by com parison with other familiar compounds of recognised strength; and in this particular, it contrasts very favourably with the variable quantities of substances often quoted, the force of their relative strength being oft-times lost in ordinary reading, through the difficulty of readily comparing the proportions. But to return to the matter of developing. In addition to the normal proportion above recommended, the judicious use of the concentrated solution of carbonate of soda is an important auxiliary in cases of under-exposure ; a (say) twenty per cent, solution of soluble bromide should also be kept at hand, and a few drops added on the first indication of the image developing too rapidly. I heard lately of one photographer trying carbonate of soda in his developer, and then giving it up because, although the result was good, it took some three hours to develop the negative. I cannot imagine what he had been doing, as in my little experi ence I find the time of developing with ammonia and the car bonate very much the same; in the latter case, probably a little longer period being necessary to obtain the requisite density. In conclusion, I may state that the two cabinet negatives which I have with me were developed, one with carbonate, and the other with ammonia, all else being equal. It may be noticed that the carbonate developed plate shows a decided increase of detail over that treated with ammonia. They were exposed for only one second in a not very quick working studio at about half past four o’clock on an April afternoon, with an intensity ratio of 4; a state of affairs, in respect to rapidity, that I regard as very satisfactory.
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