I'm thinking this would work with blank newsprint, but I haven't tried yet. Newsprint fades from exposure to the sun, causing a variety of different colors to appear on what was white paper. I've been curious as to whether this effect could be used for a very-long-term exposure, and I guess the answer is "maybe" lol
From what I was able to find on Google, the paper is treated with a stop/fix/develop process prior to exposure... Is this correct. Then apparently the image is actually captured of the paper with a scanner?