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COLOR-REVERSAL 47
The lower emulsion layer is sensitive to red light but is not sensitive to green light. Although like all emulsions, this layer is also sensitive to blue light, there is no exposure caused by blue light, since none reaches it. Thus, the lower emulsion layer registers only from the exposure by red light,
Color-reversal film has the customary antihalation backing on the base of the film and a hard gelatin antiabrasion layer over the top emulsion layer.
Color Developing. The film passes through a first developer in a manner similar to black-and-white reversal. Here all the emulsions are developed and images appear in each layer as negative black and white. A bleach dissolves the image formed by the first development and some fine-grained emulsion remains unaffected just as in black-and-white reversal processing. The film is given a second exposure (sometimes called re-exposure) in a manner quite similar to the re-exposure given to blackand-white reversal film.
In the second development, a dye of predetermined color appears along with the silver in each layer. The film is then put through a bath in which the silver is dissolved away, leaving only the dye images.
The top layer is now an image in a yellow* dye ; the middle layer is an image in a magenta1" dye; the lower layer is an image in a cyan* dye. Thus each layer provides a dye image in a color that is the complement of the color that exposed the layer. Where there was no exposure, all layers have the maximum quantity of dye and the film appears black. In the case in which a very bright white light provided the exposure, all layers have the minimum quantity of dye, and the film appears clear.
Color Reproduction. The film projector throws white light on the film. If blue light was the only light used for exposure of the film when it was placed in the camera, the top layer of the film is clear. The middle layer, being unexposed, is dyed magenta. The lower layer of the film, also unexposed, is dyed cyan. When the white light from the projector traverses the film, green rays are absorbed by the magenta (minus green) dye, and red rays are absorbed by the cyan (minus red) dye. The only portion of this white light that remains unaffected is the blue ; in this manner the blue light used to photograph the original scene is reproduced by the film that is run in the projector.
The reproduction of green is accomplished in a manner similar to that for blue. If green light was the only light used for exposure of the film when it was placed in the camera, the middle layer is clear. The top
* Minus blue : yellow. t Minus green : magenta. t Minus red : cyan.