I will be glad to see a fresh and authoritatively updated copy.
A useful reference work could be made from the combined posts in Mudcat of Malcolm Douglas (and of course Bruce O and others).

The browning is the result of sulf(ph)ur in the paper and leads to disintegration and eventual loss of the book unless costly conservation treatment is applied. I can't recall when paper manufacture entered this phase but I think it mostly affected material between 1860 and 1940 that was made with the cheaper sulfur-whitening process. Newer book papers are free (mostly) of this problem.