Colouring the emulsion using a solution of an aniline or similar dye dissolved in water.

These dyes could be applied to the print after processing and the film was immersed in the aniline dye solution for several minutes to achieve the right result. However there was also a market in unexposed film that had already been dyed so that laboratories could use this film to make prints. The dyes used for this purpose had to be fast and inert to the subsequent processing solutions.

In France, Pathe used the same nine colours that were used for stencilling, probably using the same dyes as well - not surprising, as the chemical requirements for stencilling and tinting are much the same. A list of 16 dyes used for early films in the USA for tinting, stencilling or application by brush are listed by R Ryan [see bibliography]. The various publications of the 1920's in both US and Europe list more than 100 in all. Ryan also lists a further 10 dyes that could be used for tinting sound film prints without impairing the quality of the optical sound. These are listed in the tables below.

In practice, the emulsion was tinted by winding the film to be coloured onto a wooden frame or roller that was then immersed in a dye bath. The worker agitated the frame for about three minutes, and then removed it from the bath when the desired colour was achieved and immersed it in a water wash for about another two minutes. The film was dried on the frame. Once they were dry, the various scenes of the film were ready to be edited. Tinting reduces the visual contrast so that when the positives were made it was recommended that the contrast be increased to compensate. This does not always seem to be the case in practice.

One problem with this system was that the colours were never perfectly consistent because, depending on what level the section of film was on the wooden frame, and depending on the solution concentration and the time of treatment, the colour could be more or less intense. One instruction from the National Aniline and Chemicals Co. in the USA recommends a 50 US gallon tank {with concentrations as in the table above] and suggests that between 20,000 and 40,000 feet of film could be dyed. Presumably, the first racks of film came out more deeply dyed than the last!

It is recorded in the literature that even when tinting began to be done on continuous machines the results were never perfectly uniform. Pathe was still using batch tinting in 1929 so perhaps continuous tinting hardly ever occurred. The main laboratories in the US seemed to have available about nine different colours at any one time.