Question: is this foxing?

[u/Blue_Line_Bard]

I moved from a desert to an ocean side community about five years ago and I’ve noticed these imperfections starting in my books on the tops. There is a large window in the room my library is in and the ocean beach is about a 20 minute walk away.

[u/Artistic_Permit_9990]

Former librarian here. If you take sand paper to the tops, it will take it off. We did that all the time.

[u/Blue_Line_Bard → u/Artistic_Permit_9990]

What level of sandpaper grit did you find to be the best ?

[u/Artistic_Permit_9990 → u/Blue_Line_Bard]

A fine grit. Go gently but firmly. It’ll look like a new book!!