Shooting and processing of long-expired films

[Anaxagore]

When moving my household between 2 countries, I found 2 films that may have been exposed a few years ago but that I had forgotten and had not had processed since then. Both were already out of date when I would have exposed them using the usual rule of 1 stop over-exposure per 10 years expiration compared to their original sensitivity for color (and 1/3 stop for 10 years for BW). There was one 25ASA BW negative film and one 100ASA slide film.

I brought them to a local lab that processed them and told me they were both empty, which is possible as I did not remember when/where I may have exposed them, but on the other hand why would I have opened the pouch containing these films if not to put them directly into my camera... Something, however, that surprised me is that the slide film came out all greenish (when, to me, an unexposed slide film after being processed correctly would be completely black), and the BW one came out rather grayish than all white..

That triggers a few questions I'd like to ask the community:

1a. Have you ever had slide film (especially areas between frames, which do stay unexposed) turn green after development, maybe due to the age of the film?
1b. If yes, did this happen under specific circumstances?
1c. If no, would that mean that the lab messed up the processing?

2. The +1 stop for 10 years for color negatives is a well-known rule of thumb for expired films that usually works well on color negatives (apart from the color shifts). Nevertheless:
- High-sensitivity films, if I am not mistaken, drop in sensitivity faster than lower-sensitivity films (hence the shorter best-before date when they are bought fresh)
- I suppose that the drop in sensitivity is also dependent on how films were stored (properly frozen, in temperate environments, in environments with many variations of temperature, etc.).
- Color negative films support over-exposure much easier than color slide films, and therefore applying the rule is no problem with color negatives, but could result in over-exposed slides
- I have never found online such a rule for black and white films (negative films... it would become even more complex for BW slides such as Agfa Scala!). I suppose that with fewer layers, black and white films do not need as much exposure compensation for age as color films, and sometimes they seem not to need compensation at all (Around 2010 I shot an old Isopan SS that had expired in the 1970, bracketed exposures, only to find that shooting at nominal speed was still working without problem).

The influence of storage conditions would be too difficult to evaluate for a proper study, but has there ever been a thorough scientific study that found how to make the over-exposure rule of thumb more accurate:
2a. based on initial sensitivity?
2b. based on whether slide or negative?
2c. based on color or BW?
2d. maybe even based on brand (nominal sensitivity is not always true sensitivity)?

If yes I would be very interested in getting the references, if no then I guess that finding a sponsor to pay for the films and processing in controlled conditions would be very hard, university research departments would probably not be interested in running such a study anymore, so I would like to hear from the community here about your experience with these factors (BTW together with Scala, let's also exclude Kodachrome from these questions, based on the number of layers and on the discontinuation of the process anyway. I would lump chromogenic BW together with color negatives).

 

[Donald Qualls]

The grayish B&W film is just a case of age fog. Even slow film, if poorly stored, can fog quite a bit over a couple decades. Faster films usually fog more.

With black and white films, fog is just gray density where the film should be clear (or just the base); with color films, either negative or reversal, the situation is more complex. A slide film with no fog ought to come out black if processed without exposure, but if there's fog, it'll have some color. Depending on which layers have how much fog, the color may range from orange to teal. In your case, you got a greenish color, indicating that the cyan layer likely had the most fog (which happens because, with the other emulsion layers and a filter layer on top of it, it has to be the most sensitive layer, hence more prone to thermal fog), with lesser levels in the overlying magenta and yellow layers.