If it's mold, I don't have a solution for you. Let it dry (put some other
books ontop so it does not warp), see what happens. But in general, I've
found that a lot of the smell comes from dust that's on the old books from
just sitting on the shelves for a long time. So, the first thing I do to
an antique or even just an older book when I bring it in - I vacuum it.
You got to be really careful doing it though - very easy to damage a book
if you just take a vacuum hose to it. I use a small brush attachment that
helps lifting the dust and (probably even more importantly) limits the
cross-section so the suction is not as great. Most of the dust is on the
head - the top edge - 'cause books stand upright most of their lifetime.
For some reason I also find a lot of dust and dirt between the end sheets
(first page behind the front cover or one before the back cover). There is
usually considerable amount behind the spine if it's not a perfect bound
(as in paperback) book. But look around the particular one you got - there
could be some other places you may want to pay close attention to,
depending on how the book was stored.
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