Foxing is the term for the scattered reddish-brown spots and blotches that appear on old paper, including books, prints, maps, drawings, watercolours and documents. The name is often said to derive from the rusty, fox-like colour of the stains. The word is also used loosely in the trade to describe the spotting and clouding that develops on the silvering of antique mirror glass.
The causes of foxing on paper are not fully understood, but it is generally attributed to a combination of fungal activity and the oxidation of iron or other metallic impurities in the paper, encouraged by damp and fluctuating humidity. Nineteenth-century papers are particularly susceptible. Light foxing is common and accepted on many antique prints, but heavy foxing can detract significantly from an image and from value. A qualified paper conservator can often reduce foxing by washing and careful treatment, though bleaching should only be undertaken by a specialist. Prevention is the best approach: framing with acid-free mounts, avoiding damp walls and keeping works in stable conditions. In mirrors, gentle foxing to the original plate is often appreciated as a sign of age and authenticity rather than a defect.
