Lowest possible fog developer for *very* expired black-and-white film?

I've been meaning to ask this for ages: I have a project where I'm shooting 16mm black-and-white stocks from the 1920s and 30s. Needless to say the age fog is usually very, very high. I often rate these stocks down below ISO 1 to compensate for the age, then pull-process.

Both with paper up to 75 years old and with film I've had lots of experience success using benzotriazole for anti-fog, often alongside potassium bromide. I've never used AF-2000, but if it or other obtainable effective anti-fogging agents could be used alongside additively, I'd be glad to know. Or, if there are developer ingredients I should be avoiding that are detrimental I'd appreciate knowing this as well.

My main question is: mixing from scratch, what would an ideal developer recipe look like to be most amenable for inhibiting fog on century-old materials like this? With enough light, speed loss is relatively unimportant, but the developer should at least produce a pictorially normative tonal scale.

Photo of a 1930s 100ft load of Eastman Ciné-Kodak panchromatic stock -- an example of the films I like to use.

It's simple to run some tests to determine the existing amount of fog in the film -- using 6 inch strips, or whatever's easy.

Start with an unexposed strip, undeveloped, but fixed. That gives you the base.

Then an unexposed strip, developed (at whatever time you want) & fixed. That gives you the base + fog

Then repeat with a small amount of benzotriazole (or whatever).

Keep repeating, adding benzotriazole (or whatever) until adding more doesn't help.

That will give you your development time. Run some exposure tests to determine the ISO. You can adjust the development time to get the contrast you want.

Thanks Xkaes, I know. I do a strip test and check base+fog with every ancient roll I purchase. But rather than discuss ad hoc testing, I'm asking in some sense about formulating a black-and-white developer recipe that presumes massive fog as a starting point, and potentially uses something beyond benzo.

The proper way of doing the tests is to estimate development rate: the ratio of maximum density to the fog density as a function of development time. The curve has a shape of a gentle hump. The optimum development time is near the maximum.

If you are after a practical solution, use HC-110 in dilution B or more concentrated. Develop at low temperature (below 18 C) to avoid uneven development. This is my approach with very expired film. I doubt that a perfect developer for expired film is going to achieve any noticeable improvement over HC-110.

Do you reverse your film or develop as negative?

Thank you, good advice. I've watched that "hump" happen live under night vision, when the fog begins to overtake the image density rate, and can sometimes get a feel for it well-enough to estimate for next time, even without plotting data.

I love reversal with 16mm Tri-X and 3378E, and do this a lot with students so we can project. But with very old stocks, I've always dev'd as a negative to avoid complication, then, I scan and invert.

I do have a pint of older HC-110 that I can try, though partly for economy I'm still curious as to whether there's a superior "cocktail" of anti-fog ingredients that could be mixed.

Over the past decade, I've also collected several dozen shot but undeveloped rolls of film from Bolexes. Trying to coax an image out of those found rolls is another scenario for why I'm interested in the best possible starting point, since it precludes the luxury of uninvasive testing.

I am not an expert in photographic processes but I understand that silver forming fog is indistinguishable from silver forming the image. Thus, it will require some sort of magic to reduce fog without affecting the image. Once again, it is just me guessing on how things work in photographic world.

From an economic perspective HC-110 is hard to beat especially when fancy anti-fogging agents are involved.