Wear at the edge of the paper can generate fine paper particles. This wear can occur as paper rubs camera edge guides or the edge flanges of film spools. Any winding or tracking misalignment can increase wear on the edges of the paper. Paper tears can generate larger paper particles. Again, these particles can accumulate in the camera and be a source of shadow images.
Interchangeable backs require dark slides and light traps to facilitate changing backs.
Light traps can trap foreign materials. Repeated insertion and removal of the dark slide can generate dust and dislodge loose fibers. Regardless of the source, foreign materials may be attracted to the film surface during film advancing due to static charges. Because photographers often open sheet-film cameras in the working environment, the most common sources of shadow images are dust and dirt. To prevent this from occurring, clean these areas regularly.