I read somewhere that you can use OHPs for sun printing – print a design on them, layer them over fabric painted with silk paints, leave them somewhere warm and come back to find the design printed on the fabric.
I did have doubts about whether it would. Sun printing works by evaporation, and I suspected the liquid wouldn’t evaporate under a sheet of plastic, whether it was printed or not., only round the edges. I should have trusted my instinct. It would probably work if I cut stencils from the OHPs, so I may try again later. It does prove, though, that it’s warmth that makes the print, not light.
I do have 4 rectangles of fabric with paler centres and a darker frame, so it’s not entirely wasted.