Separation methods from coloured originals - two-colour subtractive films.

Subtractive two-colour films [Cinecolor, bi-packs and DuPacs etc.] of the period from 1920 to 1950 pose a special problem. Firstly they are generally metallic colorants or basic mordant dyes, quite unlike incorporated coupler colour films, and they fade by darkening and/or changing colour. This poses real problems if it is not known what the original primary colours were or looked like. Some restorers ignore this aspect and make three RGB separations from which an intermediate colour negative [on Eastman Colour Intermediate] can be made. This copies the faded original, using modern three-colour technology, but allows some variation in saturation to be made by varying the contrast of the final colour print. As the forensic study of early colour films improves, the original colours of these two-colour primaries will be known - where they are, they are considerably more saturated than originally believed - and better methods will become available. One technique that has only been tried experimentally is to make two separations to record just the two original dyes. These separations are then printed one after the other [like A rolls and B rolls] onto modern colour print film each exposed to produce a colour corresponding to the original two colour primaries. This is an extension of the Desmetcolor method used for simulating tinting and toning.