Here's the story. I have a composition notebook that I used to write some of my math proofs in that I want to keep. In my home, the wall of the window grew a lot of mold over the winter in areas that we were unaware of. The notebook was very close to this wall (as some other things were). This notebook now has a yellowish (almost old age) tint to the pages that are near the exterior edges. To note: There was also the same type of composition notebook in the area as well (very close) but it has no yellow tint. This one is slightly older than the composition notebook that got tint on it. This leads me to believe that something happened to the younger, but similar composition notebook in almost identical places (off by a few inches). My question is, is this MOLD or is this OLD AGE? The speed at which this occurred is roughly Months to a year. I've had this notebook for about 2-3 years, but only saw tint in it in the last 6 months. The speed at which this occurred leads me to think that this is some sort of MOLD residue from the infestation. But the look/appearance makes it feel like it is just old age or something else (maybe cat pee? It doesn't smell tho...) If it is mold, should I get rid of it? Thanks for opinions.