PHOTOGRAPHIC MATERIALS 151 



The Kodachrome Reversal Process. — This process uses an integral tripack, or mono- 

 pack, with the three emulsions for making the color-separation negatives and their 

 corresponding partial-color positives coated on one support.^ Thus the difficulties of 

 handling three separate films is avoided, and exposures can be made in any ordinary 

 camera. The emulsion next the base is sensitized to red, the middle emulsion is sen- 

 sitized to green, and the top emulsion is sensitive only to blue and carries a yellow dye 

 to prevent blue light from reaching either of the lower layers. The different emulsions 

 are separated by very thin layers of clear gelatin. Since the total residual positive 

 method of reversal is used, the emulsions are very thin, and the total thickness of the 

 three combined emulsions and two intermediate layers is no greater than the thickness 

 of an ordinary negative emulsion. 



The three partial-color positives are produced during the development of the 

 silver positives by interaction between "coupling" compounds and development 

 reaction products to form dye densities proportional to the silver densities. The 

 formation of three different dye images in their appropriate layers requires a rather 

 complicated processing procedure which can be handled satisfactorily only by properly 

 controlled processing stations. 



The three emulsion layers must not only be coated extremely uniformly but must 

 be very accurately balanced for color sensitivity, speed, and contrast. This requires 

 very rigid control in manufacture. The result, however, is that the user has no worry 

 other than giving a reasonably correct exposure. 



Bibliography 



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 Benedict, H. C: Facts and Foibles in Photography, Camera Craft, 43, 226 (1936). 

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