Yup, lith film. Thanks for the info. I developed a sheet just now for 7 mins in Ilfosol-S and it's wicked high contrast, not exactly two tone but pretty damned close.
I'll see if I can salvage the rest in dilute dektol or something.
Since you have identified it as ortho-litho, you can develop it under red safelight, if you didn't already know that. Soup till it looks good under the red the red light and let it go that amount of time again. I have had moderate success taming the beast with super dilute Rodinal. When you get it to work right, its some tight stuff.
Yeah, I did that. I didn't have my paper trays out but once I figured it out I pulled 'em and the dektol out. It immediately became obvious why they didn't need notches and why there's a brown backing - it's easy to see which side is up under safelight.
Got a couple that almost looked continuous tone (1:3 of my normal paper dilution of dektol) but very little shadow details. Not surprising given I exposed it for ISO 100 (give or take - I was using a homemade lens board and a hacked together lens without a shutter, so I probably shot it more for ISO 50 or 25 as it was overcast, not quite dark enough for my handheld shutter).
Got one neg that will suit a recent cyanotype project I've been working on, so I'm actually pretty happy; I would have gone out and shot this shot exactly like this anyway if I'd known what kind of film I was shooting
I've tried it with dilute HC-110, 1+64 instead of the usual 1+32 dilution B. The stuff seemed a little slower. Dektol at about 1+7 or 1+9 is what I'm aiming to try next time around. I'll add that I'm not exposing this stuff in camera, but rather making interpositives for enlarged negatives suitable for contact printing.