At least two reasons why you should use sandwich paper, not just for sandwiches!
Sandwich paper (wax paper, parchment paper, or any other type of semi transparent paper) can also play a useful role in photography!
I recently opened the back panel of my Diana, affixed sandwich paper to the inside, threw a dark jacket over my head, opened the shutter (holding down or locking the shutter release open on the “B” setting), and discovered the world as my camera sees it. Occasionally I do it again, to compare in particular what is captured through the lens with the view through the viewfinder – this will save you many a misjudged shot and also allow you to directly compare different lenses and different focused distances with each other!
Since I already had the sandwich paper adhered to the inside of the camera, I wondered how well it would work as a frame. So I carefully tore away at the center of the square. I had thought the ripped paper would result only in a frayed border, but development revealed that the sandwich paper still let some of the light through, creating a very special semi-transparent effect around the main image!
The sandwich paper should be well adhered to the camera – In the end, my mask was ripped off and pulled into the roll during spooling. Luckily, all the pictures were already shot!