In contrast to tinting, toning is not the simple immersion of a film into a dye bath but involves a chemical reaction converting the silver image. In this reaction the neutral silver image in the emulsion of the positive film is replaced by one consisting of colored metal compounds. These were usually iron ferrocyanide (Prussian Blue) for blue, copper ferrocyanide for red/brown, silver sulfide for sepia or rarely uranium ferrocyanide for reddish brown. Toning had been used in still photography before. But since film was projected on the screen it required translucent toning compounds.
For tinting, the positive print is immersed into a variety of dye baths, scene by scene. To this end, the print has to be cut into the corresponding fragments and reassembled after the dyeing process. The dye homogeneously attaches over the entire image’s gelatin including the perforation area. Usually synthetic dyes were dissolved in a weak acid solution to form a chemical bond with the gelatin.
“In 1898 William Friese-Greene, a professional portrait photographer by trade, demonstrated in London ‘the first process of true natural-color cinematography.’ His program consisted of ‘a series of animated natural-color pictures,’ and although this demonstration aroused considerable interest at the time, Friese-Greene was unable to exploit this system on a profitable basis. Undaunted, he eventually developed a total of four different color methods.”
Kinemacolor was an additive process operated with alternating red and green filters that were applied to the shutter in front of the camera and in front of the projector. With at least 32 fps the frame rate was double the minimal frame rate of 16 fps. Time parallax with small differences between the red and green record resulted in color fringes that became visible when objects or scenes were moving.
The Kodachrome process was invented in 1913 by John G. Capstaff for still photography and subsequently adapted to motion pictures. For the process two frames were advanced simultaneously, one located above the other. The light passed either through two lenses or through a beam-splitter, fitted with red and green filters. The release print was exposed through a beam-splitter whereby the alternate frames were projected onto either side of double-coated stock. After development by a usual b/w process, the film was tanned to harden the exposed areas. The soft areas were dyed red-orange and blue-green respectively.
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.