Visual Arts Question:

Photographic film and photographic paper can display an image after a super prolonged exposure. This is because light has the ability to separate the silver salts (silver halogens) that makeup the light sensitive coat that is common to film and photo papers. You can demonstrate this for yourself. Best if you procure some black & white photo paper and a black & white film negative that displays an image. Place the photo paper outside in the sunlight and tape the film negative on its surface. No negative? Place leaves or coins on the paper. The natural action of the sunlight will cause the paper to darken. Same if you substitute film for the paper.