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2015-06-01T15:00:37+05:30

Black-and-white images are not usually starkly contrasted black and white. They combine black and white in a continuum producing a range of shades of gray. Further, many prints, especially those produced earlier in the development of photography, were in sepia (mainly for archival stability), which yielded richer, subtler shading than reproductions in plain black-and-white. Color photography provides a much greater range of shade, but part of the appeal of black-and-white photography is its more subdued monochromatic character.
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2015-06-01T15:21:51+05:30
The reaction of decomposition of light is used in this case.
When light is allowed to pass through silver chloride it decomposes to form chlorine and silver.The chlorine gas escapes and thus now the compound holds up grey color due to the presence of silver 
2AgCl ---> 2Ag + Cl2
Silver       silver   chlorine
chloride
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