Just out of curiosity, I wonder if there is any special chemical one could use to increase performances of expired film.
Let's suppose two situations:
1 old film exposed long time ago
2 old film recently bexposed
Is there something I could do to reduce fog and other issues that come with long expired films?
Thanks!
Consider increasing development time, because old film has likely lost quite a bit of speed and contrast. An initial test would run a short, unexposed test clip through the process with CD time extended to 5 or even 6 minutes, then run tests with KBr added to CD until fog is under control, with typical steps of +1 g/l. Since you will see off colors anyway, you can freely experiment with extra restrainer.
My experience is that overexposing is enough to deal with expired unused film, 2 stops for example, you can get some color shifts but perfectly usable images with standard C41 processing. I found "old" latent image (film exposed long time ago) to be far more problematic, perhaps the extended development is the way to solve it but I have never tried.
Over expose to burn through the fog. I tend to lean on a slightly longer development. You'll end up with some color shifts, weird stripes, pinholes and extra grain but that can be fixed in post generally.