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Please explain how two different, independent images were exposed onto the two sides of duplitized film. How would one keep the light from one side's image from exposing the emulsion on the other side of the film? —Preceding unsigned comment added by 216.40.140.138 (talk) 07:22, 19 April 2010 (UTC)
Duplitized film
editThis question was posed nine years ago, and I'm surprised nobody has attempted to answer it before now. On duplitized film the film-base incorporated a yellow dye which could be bleached after the film was processed. The emulsions on both sides of the base were 'ordinary' emulsions, sensitive only to the violet content of white light. One strip of the original two separation negatives - say, the red separation - was exposed to the upper emulsion layer, which would respond only to the violet content of the light to produce a positive image. The yellow dye in the film base would filter out any violet light and prevent it from reaching the emulsion on the other side. The same process would be applied to the second emulsion layer on the opposite side of the base. It would be exposed to the second separation negative - the green separation - to produce another positive image. Again, the yellow-dyed base would prevent any violet light from reaching the emulsion on the other side. The exposed film was developed and fixed, and the yellow dye was bleached out of the base. Each side of the developed film was treated separately with chemicals to convert the black-silver positive images into color images. The black positive from the green separation was treated with uranium to convert it into a red color. The black positive from the red separation was treated with iron to convert it into a cyan (primary blue) color. (The combination of red and cyan images gave more harmonious and natural-looking results than the combination of red and green images did in most early two-color processes. Red and cyan are complementary colors, red and green are not. And skies, seas, rivers, lakes and snowscapes appeared as blue, as they do in nature, instead of green.) O Murr (talk) 20:37, 26 April 2019 (UTC)