During the capturing of the film a beam-splitter in combination with filters in the camera divided the incoming light into a red and a green separation negative on black-and-white stock. When projected in the cinema the two images were combined simultaneously by additive mixture through corresponding red and green filters into one picture consisting of red and green colored light. The reduction of the whole color range to two colors (and their additive combinations) was necessary because of the complex optical arrangement.
The first subtractive 2 color process introduced by Technicolor captured the incoming light through a beam splitter with red and green filters also. However, in contrast to the first Technicolor process, the two b/w images were recorded on one negative strip. This was achieved by the pull-down of two frames simultaneously, a process that required the double speed in the camera. These two frames were arranged in pairs, whereby the green record was inverted up-side down (see image).
The third Technicolor process used the same camera as process no. II to combine a pair of frames of the red and green record respectively on the b/w negative (see image). In contrast to the former process, however, the two images were printed on one side of the positive by the dye transfer or imbibition process.
Knowing Men (GB 1930, Elinor Glyn), negative. Credit: Courtesy of BFI National Archive. Photograph by Barbara Flueckiger.
Technichrome, three-color print of bi-pack negatives, 1948. Credit: Gert Koshofer Collection. Sample No. 89. Photograph by Barbara Flueckiger
The beam-splitter prism. Source: Coote, Jack H. (1993): The Illustrated History of Colour Photography. Surbiton, Surrey: Fountain Press.
The Phantom of the Opera (USA 1925, Rupert Julian). Credit: UCLA Film & Television Archive. Photographs of the nitrate print by Barbara Flueckiger.
King of Jazz (USA 1930, John Murray Anderson). Credit: Library of Congress. Photographs of the Technicolor No. III dye-tranfer nitrate print from 1930 and 1931 by Olivia Kristina Stutz, ERC Advanced Grant FilmColors.
Credit: Image courtesy of the Academy Film Archive. Film: Gone with the Wind (USA 1939, Victor Fleming). Photograph by Barbara Flueckiger.
Written on the Wind (1956). Credit: Harvard Film Archive, item no. 3663. Photograph by Barbara Flueckiger.
Source: Ryan, Roderick T. (1977): A History of Motion Picture Color Technology. London: Focal Press.
Pénichon, Sylvie (2013): Twentieth Century Colour Photographs. The Complete Guide to Processes, Identification & Preservation. London, Los Angeles: Thames & Hudson, p. 30.
Source: Jacobson, Egbert (1942): The Color Harmony Manual and How to Use It. Chicago: Color Laboratories Division, Container Corp. of America. Credit: Faber Birren Collection, Yale University. Photograph by Barbara Flueckiger.
Source: Hübl, Arthur Freiherr von (1904): Die Dreifarbenphotographie mit besonderer Berücksichtigung des Dreifarbendruckes und der photographischen Pigmentbilder in natürlichen Farben. Halle a. S.: Druck und Verlang von Wilhelm Knapp. Photograph by Martin Weiss, ERC Advanced Grant FilmColors.
Credit: Illustration by Sarah Steinbacher, Multimedia & E-Learning-Services, University of Zurich. Source: Ryan, Roderick T. (1977): A History of Motion Picture Color Technology. London: Focal Press.
Credit: Cinémathèque française, conservatoire des techniques, Paris. Film: Test for Jour de Fête.