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A practical, additive photo process perfected in 1907 using a glass plate dusted with transparent grains of potato starch dyed red, green and blue. These starch grains act as tiny color filters, allowing light to affect a piece of film sandwiched behind the glass plate. Film is then reverse processed into a positive transparency. Graininess and spots often appear in the finished image because starch grains could not be evenly mixed.


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