Old educational film strips and Tru-vue rolls.

I've got some educational film strips and Tru-vue stereo rolls from the 40s.
The pictures were taken late 30s - early 40s.
They have a thick film base which is yellow towards amber. It's marked Kodak safety film.
Is that color normal for film of that age? Perhaps it was toned that way deliberately?

I wonder if they used hardener or some special thick film base? Or some kind of lamination even.
Now that I do a lot of reversal I'd like to make my own half frame strips so I'm especially interested in hardeners or ways to make the film resilient to handling.

Looks like just old nitrate film turned yellow, maybe.

The film base is marked "Safety Film", so it isn't nitrate stock. From more recent examples which I've seen (and had to watch, back in the day) the base could be either clear/grey, or occasionally tinted/printed instead of being made photographically. Are the films you have still flexible enough to be wound without cracking?

Is it about 35mm - the sort of thing that would be hand-scrolled through a simple projector with a gate attachment in place of a slide-changer? If so, how hard it is on the film depends on how well the roll passes through the 'gate-and-rollers thing', between the condensers and the lens mount of the projector. It would be worth getting that sorted out, to avoid abrasions or excess pressure on the film.

To create your own filmstrip-positive would mean shooting your roll (of ortho?) and home reversing it, which you are obviously well capable of doing. Does a hardener have a noticeable effect on modern emulsions ? And where could you put it in the reversal process? <--- rhetorical questions for someone who knows what they are doing, as I clearly don't with reversal-processes....

are they in colour?many of the early Eastman colour print films turned yellow and had colour fading as they aged.