Chemical methods of “restoring” faded tripack dyes.

These processes were regularly recommended in the past and there is some literature relating to the theory but the practice is exceptionally difficult. The Editor has experimented with the techniques but, not surprisingly, has never been permitted to carry out the processes on real archival film of any value by an archive! The processes generally work but a fundamental reason why they cannot be recommended is that they are impossible to control, and it is not possible to know the long term effect of the procedures on the film treated, and for these reasons the following are summarised for interest but are not advised.

One chemical process is to reconstruct the original dyes from the breakdown products that remain in the emulsion by “reprocessing” film in various solutions. Cyan dyes seem to respond to this chemical process but yellows are not so responsive. All the formulae for the tests carried out by the Editor were from verbal sources! Some of the past literature mentions that manufacturers publish chemical formulae for this procedure but none are known to the authors and certainly Eastman Kodak do not recommend this. In any case, specialised solutions are difficult handle as they need to be located in a processing machine to treat long lengths of cine film.

The only procedure that can be in any way recommended is to reprocess faded film in a modern process similar to that originally used - a negative process using CD3 [e.g. ECN2] for a faded negative film - a print process using CD2 [e.g. ECP2] for a faded print. The temperatures should be reduced to about 25C to avoid excessive emulsion softening. There is some unpredictable beneficial effect on faded cyan dyes of old Eastman and Gevaert colour print films but little effect on faded negative film.

A more effective, but drastic, chemical treatment of faded print film is to intentionally destroy a proportion of the magenta dye until a low contrast but more neutral image is achieved. Azomethine magenta dyes are very stable but are susceptible to acids. The film can be held in a 3% [about 1N] sulphuric acid solution for up to 3 hours during which time the magenta dye diminishes. Once treated until the balance is about right the film contrast is now too low and must be copied onto a high contrast internegative film to restore a print of the original contrast. This method does work - however is messy, very difficult to carry out on a long film length, can damage processing machinery and can be uneven in effect. It also seriously softens the film emulsion and it is a race against time to achieve the right degree of magenta fading before the emulsion falls off. This is also not recommended.