Named after the reddish-brown color of its blemishes, foxing is a form of deterioration that marks paper documents and photographs with rust colored splotches, spots, and specks. While foxing can negatively impact the value of collectible paper documents, it doesn’t directly affect the integrity of the paper.
While foxing is widely believed to be caused by a fungal growth, another plausible explanation is the oxidation of materials found in the pulp from which the paper was made. In either case, exposure to humidity is the common denominator.
Humidity, or water vapor in the air, can supply enough moisture for the growth of fungi and mold, which can lead to foxing. To prevent this from occurring, indoor relative humidity (RH) should be kept below 60%; ideally between 30% and 50%.
While some collectors appreciate foxing for the patina it adds to an old document, others seek to remove it (and prevent it) altogether.
Foxing Prevention Tips
Old books, photographs, and other paper documents should always be stored in a cool, dry environment. Paper is hygroscopic, meaning it absorbs and releases moisture. Even the smallest variations in temperature and humidity will cause paper to contract and expand, causing foxing and other visible damage to occur.
To prevent such damage from occurring, here are some simple, cost effective practices you can implement at home.
- Maintain and monitor a relative humidity level between 30% and 50% at all times.
- Set your AC to a consistent, year-round temperature.
- Do not store paper documents in a room with windows or doors that open to the outside. Not only does outside air contribute to fluctuations in temperature and humidity, it also contains damaging dirt and dust particles.
- Do not display or store paper documents in areas that receive direct sunlight.
- Store old books and paper documents away from heating and air vents, radiators, and other areas that may be subject to fluctuating temperatures.
- Always use acid-free, archival materials to wrap, store, or mount paper documents.
While foxed paper can be repaired, the following techniques should only be conducted by a professionally trained conservator-restorer.
Experts may choose one of two approaches to reverse foxing, with each method posing potential risks to the paper and/or ink:
- Treat the paper with a mild reducing agent, such as sodium borohydride. This agent is mild enough that it doesn’t need to be rinsed off the paper following treatment, but may not be strong enough to completely remove the foxing.
- Treat the paper with a stronger oxidizing agent, such as sodium tetraborate. Stronger and more aggressive than reducing agents, an oxidizing agent must be rinsed out of the paper following treatment.
In either treatment, the weight of the paper will dictate how the agent is mixed and applied; hence another reason to use the services of a conservator.
While these are methods used by professionals to remove and mitigate foxing, there are unscrupulous (or uneducated) dealers that will use bleach to remove foxing. The use of bleach will cause the paper to quickly degrade. Application of bleach will be marked by its odor, wrinkled paper, and possible ink bleeds.
Due to the risks posed by foxing removal techniques, many antique book and ephemera dealers and collectors simply choose to leave foxing alone. Instead, they focus on foxing prevention techniques that halt further damage.