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Subtractive Processes 625
the future will be one which carries each picture as a finished colored result. Many have been and are still striving towards this end, chiefly by the two-color methods, which obviously reduces the essential operations, and the results are in some cases fairly satisfactory.
First as to the filters to be used for the two-color process. G. A. Smith, (see p. 596) who was the first to apply two-colors to motion picture work commercially, used at first for taking the negatives, a red filter that could be matched by one composed of yellowish eosin 9.5 g., filter yellow 2 g. per liter of gelatin solution with approximately 7 ccs. per 100 qcm. The green filter was a very blue-green, that could be matched by rapid filter green 1 g., naphthol green 0.6 g., and filter yellow 0.3 g. For projecting the red filter could be duplicated by rose Bengal 6 g., filter yellow 3 g. But the taking filters were subjected later to some change. According to C. X. Bennett41 the first filters, as above, were the YYratten & Wainwright regular tri-color red and green, but a special light pair were used for recording brilliant sky and sea effects. This red transmitted to about D l/2 E, while the green was distinctly more bluish-green. Bennett said: "with these 'light' filters blues are rendered far brighter than before, as are also artificial greens, by virtue of their large blue-green content. Exposures are also very much shorter. On the other hand, grass and foliage green are reproduced in the resultant two-color image as a bronze brown. Upon my introduction to the theory of the process it was explained to me that this browning of natural greens when using the 'light' series filter set was due to the green content passed by the orange filter, but the explanation was fallacious ; the true reason of the difficulty having to be sought in the swamping action of the additional greenish-blue rays passed by the green filter, as was speedily proven by experiment. The problem then remaining for solution was how to obtain a set of two-color filters as light as possible, so as to allow of very short exposures (a necessity in the Kinemacolor system of cinematography) and at the same time give renderings of foliage shades which were at least green and not brown. The solution was found to be in the employment of a small proportion of pure blue, or even blue-violet, light in the form of a restricted transmission band in the green filter wherewith to make the necessary records of blue objects, at the same time cutting out the offensive blue-green rays from little b to ¥l/2G or thereabout."
It is open to argument whether Bennett was right as to the swamping action of the additional blue-green and greenish-blue, as the emulsion is least sensitive to these colors, and the reflection spectrum from the average foliage is only 50 per cent of the incident light between E and F, which contains the above colors. And bearing in mind that the Kinemacolor pictures were additive and not subtractive on the screen, the bronzing of the greens would be due to insufficiency of action in the negative, which would mean greater density in the positive and consequent suppression of