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MODERN DEVELOPERS

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until it smells of sulphurous acid. The suspended matter in the solution is now filtered off, and the hydroquinone extracted from the fiiltrate by means of ether, which is subsequently distilled off, leaving the hydroquinone in its characteristic form. Until recently almost all the hydroquinone used in America and Britain was manufactured in Germany, but it is now produced by several firms in America equal to the highest European pre-war standards, e. g. Gennert's Gold Label hydroquinone. In today's practice hydroquinone is Characteristic; generally employed in combination with Capacity • other developers, bemg seldom used alone, e. g. as pyro is commonly used, except in copying and lantern-slide work, wherein its characteristic capacity for giving great density, with clear shadows and brilliancy of gradation is of obvious advantage. Compared with pyro, hydroquinone Comparisons keeps better in solution, does not stain the fingers in use, and gives negatives of a blue-black color similar to that obtained with ferrous,. oxalate. In comparison with metol and rodinal, it is a slow-acting, "hard" working developer, yielding "snappy" negatives with strong contrasts. .._.a f Hydroquinone has the disadvantage .......uence o of bemg · very suscep t"bl · t"10ns Temperature 1 e t o vana of temperature. At a low temperature it is apt to crystallize out in its solutions, which either brings development to a standstill or slows down its action; in any event cold hydroquinone developing solutions mean loss of detail and density in the negative. Advantage may be taken of this by the use of cooled solutions for the development of negatives known to be grossly over-exposed. Normally it is advised to keep a hydroquinone developing solution at a temperature of 65° Fahr. In cold weather this may be raised to 70°. Increase in temperature, however, tends to excessive density and fog, this tendency varying according to the character of the plate in use. Used alone, hydroquinone is generally Bow Uaed made up with potassium or sodium carbonate, and these carbonate alkalies are advised, although the use of a caustic alkali gives

Modern Photographic Developers  

A Practical Handbook to the New Developers Telling What They Are and How to Use Them with Reliable Formulae by The Photo Miniature, January...

Modern Photographic Developers  

A Practical Handbook to the New Developers Telling What They Are and How to Use Them with Reliable Formulae by The Photo Miniature, January...

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