"Foxing" is a mildew spore caused by changes in relative humidity ie; damp, and accellerated by (F)errous (OX)ide (iron) in the paper and ink.
From the late 18th century paper manufacturers have been adding chemicals to the paper in it's pulp state, chemical wood pulp as opposed to mechanical wood pulp.
1st edition Dickens are notoriously famous for it's foxed plates and clean text as both types of paper were used.
The course of action often depends on the severity of the of the foxing, in the case below there are other stains involved that need to be identified to determine how many baths are needed and how this will affect the integrity of the structure of the paper and the media involved.
Period Fine Bindings have developed a unique aqueous formulae that neutralises the spore and removes it without any detrement to the paper or ink.
For more information Contact Paul Tronson at: