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#11
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Graded paper
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#13
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Graded paper
UC wrote:
My question concerns solely how various grades of paper are maunfactured without showing significant color differences. I have not identified a mechanism in the literature, Probably trade secrets. I think it's already been covered... they use the same average grain size but vary the distribution. The details of crystal growth and ripening are trade secrets for a particular paper, but quite a bit has been published. |
#14
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Graded paper
Michael Gudzinowicz wrote: UC wrote: My question concerns solely how various grades of paper are maunfactured without showing significant color differences. I have not identified a mechanism in the literature, Probably trade secrets. I think it's already been covered... they use the same average grain size but vary the distribution. OK. I looked in Mees (From Dry Plates to Ektachrome Film) again last night, and despite a wealth of information on every conceivable topic relating to the manufacture of sensitized goods, this particular was not disclosed. I am writing a book about 35mm technique, and a short treatment of grain size distribution is part of the discussion about how to get the finest grain in 35mm work (which is not by using fine-grain developers, by the way). By increasing exposure a little and decreasing development a little, more small grains are developed and fewer large grains are developed completely, giving fewer 'holes', which produces the grain we see. Also, infectious development is reduced. Would you care to review the manuscript? Respond to: uraniumcommittee ---- @ ---- yahoo.com The details of crystal growth and ripening are trade secrets for a particular paper, but quite a bit has been published. |
#15
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Graded paper
UC wrote:
By increasing exposure a little and decreasing development a little, more small grains are developed and fewer large grains ... In other words reduce the EI and development time for finer grain. I'd think it as reasonable to reduce the ph. Ph has, apart from the film itself, the single most influence on grain size. Should not that hold for print emulsions as well? Dan |
#16
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Graded paper
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#17
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Graded paper
"Michael Gudzinowicz" wrote in message news:SaNKf.3554$0z.2033@trnddc01... UC wrote: How are the grades of graded paper made different in contrast? Grain size? The simplest way would be through variation of the distribution of grain sizes. If you have a broad distribution, large grains would be exposed at lower light intensities than small grains, extending the response (low contrast; long exposure scale). With a very narrow size distribution, you move toward an all-or-none effect, where a small increase in exposure will completely expose the smallest grains (high contrast grades; short exposure scale). Additionally, the grains are chemically sensitized, and I'd imagine that there are patents related to that, blending, etc. as well as trade secrets. If you want to change the contrast of high contrast paper or lith film, or extend the scale of pictorial film, the film or paper may be treated with a very dilute proportional reducer (ferricyanide) prior to development. That treatment lowers the "contrast" of the latent image (actually it reverses some of the exposure by removing latent silver centers). That approach is outlined in my reply at: http://www.largeformatphotography.in...ic/505080.html Richard may have more detailed information - I think he has a reference books on emulsion making. I haven't looked at that literature for a long time (decades). I don't have anything reliable on emulsion making. I have noticed that image color varied from grade to grade in some of the older graded papers. By old I mean those of fifty years ago. I think current papers use blended emulsions with different sensitizing. There are also dopants that affect the contrast, but I don't have details. One would have to know much more chemistry than I do and go through fairly recent journal articles and patent literature to find out what current practices really are. -- --- Richard Knoppow Los Angeles, CA, USA |
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