My proposal is to get liquid emulsion, covering large surfaces, and then testing natural found shutters.
Ex: Opening a door, walking through it, and shutting the door again is a natural shutter. The capture happens if the room I exit is lit and the room I enter is dark, and the wall opposing the doorway in the dark room has an emulsion surface.
A motion sensor light that times out after a while is a natural shutter.
The sun rises and sets is a natural shutter.
I think something standardized might be nice if I wanted to compare things in a type. I think something I mixed & applied myself would not be standardized enough, and I might have to buy something premade, but this might not work with scale.
I am looking at other things like natural dyes and cyanotypes (anything light sensitive), I will be doing media studies & trying to get down cost.