Nature has a short blurb about chemical treatments to neutralize copper in medieval iron gall inks . This ink was the major ink used for centuries for treaties and drawings. The iron preparations used to make the ink also contain copper, along with the trace metals manganese and chromium. These metals generate free radicals which then attack the parchment. The new results suggest that the minor metals are even worse than the known effects of iron.
The antioxidant treatment, combined with alkali (to reduce acidification), is dissolved in heptane and ethanol. Since it is not water-based, it will not cause the books to swell and won't dissolve most inks.
A general history of Iron Gall inks is here. A link to the Metals-In-Paper conservation effort is here. A recent abstract from the Slovenia group is here.