I cannot remember where I got the idea from! To paint on x-raysheets. I think I didn't have any canvasses on hand at that time and the only thing just as useful as a canvas, was a pack of x-raysheets on my bookshelf. So, why not try them?
The smooth surface worked excellent, especially when using a palette knife tot paint with. Here are examples of my paintings on x-raysheets. I sold many of them. I prefer to frame them and also mount them. Then I know they are protected and will last forever! A matt glass in front is nessecary.
One wonderful advantage is that x-raysheets are available from hospitals, your own cupboards or from friends! No cost at all!