Tint, tone and other colour processes
Over the years a number of methods have been used commercially to introduce colour to the projected image.
A tint is an even layer of dye added across the image which does not change in colour. Tinting was performed in two ways:
- Early tinted prints (pre 1920s) had the tint added after processing. The dyes used in the tinting solution was either acidic or basic. Acidic dyes were alkali salts of organic acids and basic dyes were chlorides, sulfates etc. of organic bases. A problem noted at the time was that some dyes, if used in concentrations stronger than 1 per cent, would attack the gelatin causing it to become brittle.
- Post early 1920s Kodak produced release print material with the tint incorporated in the base during manufacture.
Post tinting was still used in short runs after the introduction of tinted bases.
Variations on tinting included handcolouring and stencil colouring the image (Pathecolor). These labour intensive processes were in use until the late 1920s.
Toning used a chemical process to alter or replace the silver metal image with an inorganic compound or a dye colourant. Simple examples of this process is a sepia tone where the silver was reacted with sulfides to deliberately form a brownish silver sulfide image.
Occasionally tints and tones were applied to the same piece of film to produce multicoloured results.
Bipack printing used a stock coated on both sides with an emulsion. The original photography was shot on black and white film through complementary filters (an orange/red and green/blue). The emulsion on each side was separately toned by floating the film across the surface of each toning solution,orange/red and green/blue. The two layers toned in complementary colours were able to represent a variety of colours on projection.
Dufaycolor was another popular process and was a variation on the earlier Lumiere Autochrome process. Dufaycolor used a panchromatic black and white reversal film with a reseau, or grid, of fine lines of semi-transparent orange, cyan and green printed onto the film base. The film was exposed through the reseau. After reversal processing the projected image gave a good representation of the colours of the original scene.
Lenticular colour gained a degree of popularity in home movies. A filter with three bands of red,green and blue was fitted to the lens of the camera, (Fig 5.11). The lenticluar film was exposed through the base which was embossed with minute cylindrical strips, lenticles, that acted as lenses. Each lenticle formed an image of the banded filter so that the colour separations of each point of the image were recorded.
To view the full colour record the filter was placed over the projecting lens and the projected image would appear in colour, (Fig 5.12b).
The most commercially successful pre-1950 colour process was dye transfer or imbition printing. This process used three dye layers, one for each colour separation, each applied in register to a film base carrier. The best known example of this process is Technicolor.
Because of the wide range of process and formulations used before beginning any treatment on one of these early colour processes testing needs to be carried out on a test section.