What Is Foxing? — Understanding the Brown Spots on Old Paper
Foxing is the term used to describe the brown, reddish-brown, or yellowish-brown spots and stains that develop on the pages of books, prints, and other paper-based materials over time. The word has been used in the book trade since at least the mid-nineteenth century, and its etymology is debated — it may refer to the fox-like color of the spots or derive from an obsolete use of “fox” meaning “to become discolored.”
What Foxing Looks Like
Foxing presents as spots of varying size and intensity scattered across the paper surface. The spots can range from tiny pinpoints barely visible to the naked eye to blotches several centimeters across. They are typically darker at the center and fade at the edges. Foxing tends to concentrate in the margins and on blank leaves, though it can appear anywhere on a page.
Under magnification, foxing spots often show a halo effect — a darker central area surrounded by a lighter ring where the staining has diffused through the paper fibers.
Causes
The exact cause of foxing has been debated for over a century, and scientific research supports multiple contributing mechanisms:
Metallic Impurities
Iron and copper particles embedded in the paper during manufacture act as catalysts for oxidation. Under humid conditions, these metallic particles oxidize and produce the characteristic brown iron-oxide staining. Electron microscopy has identified iron particles at the center of many foxing spots.
Fungal Activity
Microscopic fungi colonize paper surfaces, particularly in humid conditions. The metabolic byproducts of fungal growth discolor the paper. Some researchers have identified specific fungal species associated with foxing, including species of Aspergillus, Penicillium, and Chaetomium.
Combined Mechanism
The prevailing scientific view is that foxing typically results from both mechanisms working together — metallic impurities create local conditions (moisture attraction, chemical reactivity) that favor fungal colonization, and the resulting biological and chemical activity produces the visible staining.
Contributing Factors
Foxing is promoted by:
High humidity — the most significant environmental factor. Relative humidity consistently above 65% dramatically increases the risk of foxing.
Temperature fluctuation — cycling between warm and cool conditions causes condensation on paper surfaces, providing the moisture that foxing requires.
Paper composition — papers with higher concentrations of metallic impurities, certain sizing agents, or residual manufacturing chemicals are more susceptible. Nineteenth-century papers are particularly prone because of the industrial manufacturing methods used during that period.
Poor air circulation — stagnant air around stored books creates humid microclimates conducive to foxing.
Impact on Collecting
Condition Assessment
Foxing is a common condition issue that dealers and collectors assess on a spectrum:
“Light foxing” or “occasional foxing” — a few small spots, typically confined to margins or blank leaves. This is considered a minor defect for most pre-twentieth-century books.
“Moderate foxing” — more widespread spots affecting text pages. This is a more significant condition issue that moderately reduces value.
“Heavy foxing” — dense spotting that obscures text or affects illustrations. This is a serious condition problem that substantially reduces desirability and value.
Period Tolerance
The market’s tolerance for foxing varies by the age of the book:
Fifteenth–seventeenth century books — foxing is expected and tolerated. These books are valued for their historical significance regardless of moderate foxing.
Eighteenth–nineteenth century books — foxing is common and moderately tolerated, though clean copies command premiums.
Twentieth century books — foxing is considered a more serious defect. Collectors of modern first editions expect clean, bright pages, and foxing significantly reduces value.
In Catalog Descriptions
Dealers are expected to disclose foxing in their descriptions. Standard phrasing includes specifying the degree (“light,” “moderate,” “heavy”), location (“to prelims,” “throughout,” “to plates”), and whether it affects the text or illustrations.
Prevention
The most effective prevention is environmental control:
- Maintain relative humidity at 45–55%
- Keep temperature stable at 65–70°F (18–21°C)
- Ensure good air circulation around stored books
- Avoid storing books against exterior walls, in basements, or in attics
Treatment
Treatment of foxing should be performed by a qualified paper conservator. Methods include aqueous washing, chemical bleaching, and enzyme treatment. Home remedies (bleach, lemon juice, sunlight) are likely to cause more damage than the foxing itself.
Foxing is one of the inevitable realities of collecting objects made from organic materials. It cannot always be prevented, and it cannot always be removed. But for collectors, it is one more aspect of condition assessment — a factor to evaluate honestly, describe accurately, and weigh alongside the book’s other qualities when making collecting decisions.
When buying a foxed book, examine whether the foxing affects the text or plates (more serious) or only the margins and preliminary pages (less serious). Marginal foxing on otherwise Fine copies is a common compromise that allows collectors to acquire important titles at significant discounts.