Someone here is bound to have some experience - I can’t find any commentary elsewhere…
I sometimes teach in a classroom with an overhead projector and a stack of blank 8-1/2 x 11 transparencies. After each class I laboriously clean off each film with water, but it still makes a mess of me and everything around me.
Plus, the films are smaller than the projector panel, so a lot of “area” gets wasted.
It occured to me that an improvement would be to mount a roll of full-width film on the front of the projector and have it feed a take-up reel at the back, then just swab it with a sponge when the roll runs out and you’re rewinding.
I went to the 3M (projector manufacturer) web site and what do you know, they had exactly what I was looking for as an attachment for their machines.
Wow. I haven’t seen roll-fed OH projector film in 25 years. More accurately, I haven’t seen the stuff actually used in about 30 years, but our projectors had the brackets for it.
You’d need to re-wind it back in screen-sized bits - wash and dry, roll it in, wash and dry, roll it in, lather, rinse, repeat.
You may have better results with dry-erase pens, as they’d just need scrubbing off with a towel or a whiteboard eraser as you rewind the roll.
This is exactly what was used in all the lecture halls at my alma mater. Even the smallest classrooms had a pair of overhead projectors, while the largest had four of them projected on large screens. I think the professors used grease pencils and would roll the transparency during the lecture. (We used to wonder who had the job of cleaning all of those rolls.)
Yeah, I have to get the sheet film bone dry before I can stack it. I figured I could rig up a multi-fingered squeegee with three or four dry towels after a wet leading edge, but I’m worried that it really also needs a few moments to air dry, as gotpasswords indicates.
The rolls have 100 feet of film on them, so I’m hoping it’s practical to use the whole roll before the clean/rewind step, but I’m concerned that the wet-erase marker ink might start to bond if it sits too long uncleaned.
I’ll have to experiment with dry-erase markers and grease pencils.