Stains, specks, spots and blotches in paper. The cause or causes of foxing, which usually occurs in machine-made paper of the late 18th and the 19th centuries, are not completely understood, but in all likelihood, it is fungoid in nature.¶ Two signi

Stains, specks, spots and blotches in paper. The cause or causes of foxing, which usually occurs in machine-made paper of the late 18th and the 19th centuries, are not completely understood, but in all likelihood, it is fungoid in nature.

¶ Two significant differences between foxed and clean areas of a paper are the higher proportion of acid and iron in the former, although there does not seem to be any clear and definitive relationship between iron and foxing. Insofar as the acid is involved, it is not clear whether this is produced chemically or as a byproduct of the life function of the organisms present.