Yeah, I guess I omitted that step as I'm not entirely sure how the actual lithography was performed. I remember a large "camera" where the negative would go into the top and the sheet would lie underneath. It looked vaguely like the reverse of an old acetate overhead projector.
How the image was etched in that process I simply don't remember, but I do remember the sheet going through a number of chemical baths and washings (and being reminded to stay clear of the chemicals as a child).
So there may have been some phase where the sheet was treated with a photosensitive chemical before going into the camera, I simply don't remember the detail.
This link [1] seems to have some details.
It looks like the plates run for a little over $1/plate for the smaller ones. [2]
Guessing it was something like an Agfa photostat camera. We had one of those at my first job. We used it both for making camera-ready art for ads (we were a tiny business) or positive film to send off to the PCB house to get boards made.
IIRC, the film was standard Kodak 8.5x11 size negatives and the processing was pretty simple. I would do everything from initial tape & wax puppets to the final artwork. Not what I expected to be doing in my first engineering job, but it was fun.
I took a printmaking class sometime later. I think the litho "stone" is made photosensitive and etched, but that aspect of the process is fuzzy. Most of the class was about positive prints and I spent most of my time doing intaglio and lino block printing.
How the image was etched in that process I simply don't remember, but I do remember the sheet going through a number of chemical baths and washings (and being reminded to stay clear of the chemicals as a child).
So there may have been some phase where the sheet was treated with a photosensitive chemical before going into the camera, I simply don't remember the detail.
This link [1] seems to have some details.
It looks like the plates run for a little over $1/plate for the smaller ones. [2]
1 - http://www.offsetprintingtechnology.com/sub-categories/offse...
2 - https://www.valleylitho.com/acatalog/Valley_Litho_Supply_Pla...