> One other comment: the very old books will probably be around for a few centuries more after the newer ones have turned to dust.

Future historians will curse the 19th and 20th centuries for switching to acidic paper. Thankfully more and more books are printed on acid free paper via ISO 9706.

From my experience this seems to be an American thing. I have US-printed books that I bought brand new about 15 years ago that look 100 years old today. On the other hand the Brazil- or France-printed books are still good as new. The paper color they use in Brazil is also very different (white as opposed to yellowish brown).

This isn't every US book though, seems to be mostly the fiction kind. The tech books I have are US-printed and are holding up perfectly.

But yeah the acidic paper thing is real and a big problem. The book I’m currently reading has these rust-like vertical streaks covering every single page. I don’t know how to recover or preserve them.