foxing

Foxing is a discoloration phenomenon in which brown, orange, or reddish spots appear on paper and paper-based objects. It is most commonly observed on old books, manuscripts, photographs, and drawings. The spots vary in size and shape and can coalesce into larger stains. Foxing is not a single disease but the result of multiple interacting processes.

Most researchers regard foxing as the result of a combination of biological and chemical factors. Fungi and other microorganisms may colonize paper in the presence of humidity, temperature fluctuations, and limited air circulation. In addition, paper can contain trace metal ions, such as iron and copper, which can catalyze oxidation reactions that darken fibers. The precise interplay is debated, and foxing can occur on papers of different ages and manufacturing methods.

Wood-pulp papers and those with high lignin or acidic sizing are particularly susceptible, though foxing can occur in other papers under favorable conditions. Environmental factors such as dust, poor ventilation, water damage, and mold growth can worsen the appearance of foxing.

Prevention focuses on stable environmental conditions: moderate temperatures, relatively low and stable humidity, and good air circulation; storage in acid-free, buffered, or lignin-free materials; and protection from mold sources and water exposure.

Treatment is typically limited to professional conservation. Methods may include careful surface cleaning, deacidification, and, in some cases, whitening or bleaching, but these interventions carry risks and are not guaranteed to remove all foxing. In many cases, stabilization and proper storage are prioritized to prevent further deterioration.