As photographic film ages it degrades. In simplistic terms, the film’s apparent sensitivity to light decreases over time. Theoretically, the degradation starts to becomes evident after the expiration date set by the manufacturer. So, it would be nice if there was a formula which could prescribe the proper compensation required for any roll of expired film. I naïvely started to work out a formula, but having limited data points, the task was futile. Instead, I decided to compile results based upon a system of rules of thumb, which are listed below.
After sharing my findings here, others have in turn shared their findings with me. With permission of the inventors, I am re-sharing their techniques, and any data they were able to provide. If you have a technique that isn’t already covered and would like to share it, then send me an email at email@example.com and I will add it to the list.
For each film I would guess at a rule for how many years it would take for that type of film’s performance to degrade one stop. In the formula that rule will be called the degradation factor, or simply the factor. Then, I would calculate the age of the film in years. Finally, simply divide the age by the factor. The result is the number of stops to decrease the expired film’s speed by.
The formula is: ((YYYY + NN/12)-(ZZZZ + MM/12))/FACTOR, where:
YYYY is the current year
NN is the current month
ZZZZ is the year the film expired
MM is the month the film expired
FACTOR is the number of years needed to drop 1 stop (e.g. 1 stop / 25 years => FACTOR = 25).
For a film with a factor of 30, which expired 10/1998 and is to be shot 7/2023, the formula would be ((2023 + 7/12) - (1998 + 10/12)) / 30. The result of that calculation would be 0.825. In this case I would round down from 4/5 of a stop to 2/3 of a stop, though using a full stop could also make sense.
These rules of thumb apply to film with an unknown storage history, and assumes the film was probably not stored properly. They will be be updated as new data points are recorded.
Panatomic-X — no compensation because it’s a miracle film.
The following examples were shot in the last 2 years (2021-2023).
AgfaPhoto APX100, expired 2009 — EI 50
Efke KB25, expired 2013 — EI 20
Efke KB100, expired 2012 — EI 25
Efke KB100, expired 2012 — EI 32
Efke R50, expired 2013 — EI 16
Efke R50, expired 2013 — EI 20
Kodak Panatomic-X (FXP120), expired 1989 — EI 32
Kodak Tri-X pan 400 (TX120), expired 2004 — EI 160, 6½ minutes in HC-110 Dilution B (1+31) @ 68℉
Kodak Verichrome Pan (VP120), expired 1989 — EI 50
Kodak Verichrome Pan (VP127), expired 1966 — EI 25
Kodak Verichrome Pan (VP620), expired 1964 — EI 25
ReraPan 127, expired 2014 — EI 64
A few helpful notes:
It seems that the Efke films [mentioned above] either had exaggerated speed ratings when manufactured, were mislabeled when the lots were purchased, or have aged poorly. They were frozen since 2015 but their speeds were terrible.
Benzotriazole reduces fog. The only way to really use it is to pre-dissolve it in a 1% solution of water, and add to your tank. But it does slow sensitivity of the film (no free lunch) even further. Also I ran a test with identical exposures, cut the roll in half, developed one half with benzotriazole and one without. After scanning, correcting for the base fog level, the images were indistinguishable. I think benzotriazole was more useful in the optical printing days - I guess even today if you are printing that way. I think with scanning, it’s much easier just to “scan through.”
I used to extend development time on expired film in an attempt to get back some of the lost dynamic range. Again, I think that might have been useful in optical printing. The grain really suffers though, so that for a scanning workflow, normal development and aggressive or two stage curves layers are a better bet.
Even Pan-X can be wrecked. I bought an 8 roll lot of 120, and the boxes were in perfect pristine condition. When I loaded the first roll I did notice that the ink on the wrapping paper looked faded. Anyway, the roll was completely cooked, either by heat or radiation. Second roll, the same, as was the third. Aside from this lot, every roll of ancient pan-x has worked out perfectly.