COLOR PHOTOGRAPHY 661 



combination of a bipack and a third separate film. The light beam emitted from the 

 lens is split up by a glass cube made up of two right-angled prisms cemented along the 

 hypotenuse, this being slightly coated with a reflecting metal, such as gold or silver, to 

 a definite reflection-transmission ratio. The lenses of a Technicolor camera are 

 specially designed to work in connection with the prism block. The fact that the 

 dyes have a slight tendency to wander and the difficulty of transferring three-dye 

 images in absolute register by automatic means tend to make any process of this type 

 not quite so critically sharp as black and white. In addition, one of the negatives is 

 in itself slightly diffused, being the back negative of the bipack. 



Motion-picture film in color, by the combination of dye mordant and dye transfer, 

 is ordinarily carried out by using a positive film coated with emulsion on both sides 

 with the two most important colors, magenta and blue-green, printed back to back. 

 These two-color images are produced by first treating the silver images with a mordant, 

 such as copper or iodine, then floating each side on the appropriate basic dye 

 bath. The third color, yellow, is obtained by transferring a yellow dye to one side or 

 the other, by means of a wash-off relief matrix, in substantially the same way as is 

 done with Technicolor. Color-positive films by the Brewster and Cinecolor processes 

 are somewhat along these lines. 



The positive blue image can also be produced by strictly chemical toning, such as 

 iron toning described before; the magenta can be produced by dye mordant, and the 

 yellow by dye transfer. 



Presumably, the magenta and blue-green images on the double-coated stock could 

 also be produced by means of the Chromatone toning process, by first bleaching the 

 complete film in the red and blue Chromatone toner A, and then floating each side 

 onto the appropriate B toner. In this case also the yellow would have to be applied by 

 transfer. 



Color images produced bj^ chemical toning or by dye mordant are usually sharper 

 than images produced by dye transfer. However, the problem of correctly printing 

 the partial images in exact register is common to both methods. 



Very promising are the new tripack subtractive films issued by Eastman Kodak, 

 under the trade name Kodachrome, and by Agfa, under the name new Agfacolor. 

 The three emulsions in these tripacks cannot be separated. 



The colors in a Kodachrome tripack are introduced in each layer after development 

 by very elaborate and carefully controlled operations. The new Agfa color film, on 

 the contrary, has embodied in each layer the nondiffusing color formers. When the 

 film is developed in a coupler developer, these color formers combine with the oxidation 

 products of development to form insolvible dyes. The new Agfacolor is obtainable in 

 both the reversal and negative-positive form. With the reversal type the coupler 

 developer is used only during the second development, while with the negative-positive 

 type the colors in a negative are produced during the first development, and the nega- 

 tive is subsequently fixed and cleared of the silver image. The positive is produced 

 by printing this negative on a similar film, which is again submitted to the action of a 

 coupler developer followed by fixing and removal of the silver image as done with the 

 negative. 



The new Agfacolor will probably be available in the future for making color prints 

 on paper, as well as color motion pictures. Little is known at this time about the 

 stability of the colors produced by this chemical method. 



The complicated manufacturing process of both the Kodachrome and new Agfa- 

 color might render these films too expensive for color-positive motion-picture releases 

 at the present time. It is therefore very likely that the immediate use of these films 

 will be for the purpose of replacing the multiple negatives in the present motion- 

 picture camera, thus permitting greater speed and economy of light. The release 



