Likely slow speed orthochomatic film used for making printing plates. Comes in a 9" width; might be deisgned to allow printing of 8.5" final copy with edges of the material held in the printing frame.
Might be very thick gelatin silver mix, expose to UV, and the wash the unhardened gelatine off, then further harden the remaining gelatin in formadehyde, and use it fp photomechanical offset plates.

These are wild guesses. Pull some out in the aboslute dark, snip off a bit. Put some in paper developer for say 5 minutes in the dark, fix after dev, then lights on, to see how fogged it is.
Second part fix directly to see how dark the base is.

After that, expose a next snip to incandescant light for measuresd reproducable amounts under the enalrger - start with something like f/4 30 seconds, to see if you can put any back exposure onto it.

Go from there - scientific method. Hypothesis, test, adjust, iterate.