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How long does Agfa MCC Fiber paper last at room temp?
"zach" wrote in message ... On Mar 28, 4:57 am, " wrote: How long does Agfa MCC last at room temperature? I just purchased a batch thats around 5 years old. Regards Bob McCarthy I think the biggest factor to aging is from neutrons emitted from the sun. kodak had/has an under ground site under ?Lake Erie? that has the density to block most of these wave lengths. Freezing slows chemical reactions so it may help reduce the prior effect...Sorry I don't have more specifics. I too have used 3+ year old paper with acceptable results and those without. Not sure if you mean neutrons but some cosmic rays can affect the fastest emulsions. In general paper emulsions are too slow to be fogged from this cause. Most fogging is caused by a contuation of the chemical process by which the silver halide crystals become more sensitive in manufacture. This process is called ripening. While it was done by slow cooking of the emulsion in the past it is now done on a continuous basis by chemical additions. With either method other chemicals are added to stop the process when it progresses as far as desired. However, the ripening processes never stops completely and some "fog" crystals are produced. These halide crystals will develop into metallic silver without exposure. They are undesirable but inevitable results of the ripening process. Emulsions contain anti-fogging agents and stabilizers to prevent the generation of fog crystals but they will eventually be produced. This is only one of the chemical processes in the emulsion which continue to some degree after manufacture and which cause fog. Oxidation at the surface of the emulsion is another cause of fog but unopened packages of paper or film are not likely to suffer much from this. Since all chemical processes are increased by temperature storing sensitive materials at low temperatures is desirable for long shelf-life. Some of the stabilizers used in the past, for instance cadmium, are no longer used because they present an envirionmental hazard, as a result, film and paper manufactured in the last about decade do not have as long a shelf life as in the past. It appears that variable contrast paper, for various reasons, is not as long lived as graded paper, but warm toned emulsions also seem to suffer more from age than cold tone ones, perhaps because of the fineness of the grain. Paper which is only moderately fogged can often be salvaged by using benzotriazole in the developer. Benzotriazole is a powerful anti-fog angent, more effecitve than bromide when used in photographic developers, and has relatively less effect on emulsion speed. Either benzotriazole or bromide will affect speed, image color, and characteristic curve, to some degree depending on the nature of the material and the amount used. -- -- Richard Knoppow Los Angeles, CA, USA |
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