Foxing on Books — What Causes Those Brown Spots and Can They Be Removed?

Foxing is the term for the scattered brown or reddish-brown spots that appear on the pages of old books, prints, and other paper objects. The name has nothing to do with foxes — it likely derives from the fox-brown color of the spots, or possibly from the old English verb “fox,” meaning to deteriorate. Whatever its etymology, foxing is one of the most common condition problems in rare and antiquarian books, affecting everything from 18th-century novels to 20th-century first editions.

What Causes Foxing?

Despite centuries of observation and decades of scientific study, the exact causes of foxing remain incompletely understood. Two leading theories, which are not mutually exclusive, account for most cases:

The Fungal Theory

Many researchers have identified fungal activity as a primary cause of foxing. Microscopic examination of fox spots frequently reveals fungal hyphae (the thread-like structures of fungi) within the paper fibers. The fungi metabolize components of the paper, producing the characteristic brown discoloration.

Supporting evidence:

• Fungal species (particularly Aspergillus and Penicillium) have been cultured from fox spots.
• Foxing is more prevalent in humid environments, consistent with fungal growth requirements.
• The scattered, circular pattern of fox spots matches the growth pattern of fungal colonies.

The Metallic Impurity Theory

An alternative or complementary explanation attributes foxing to tiny metallic particles — particularly iron — embedded in the paper during manufacture. These particles oxidize over time, creating localized brown stains.

Supporting evidence:

• Chemical analysis has detected elevated iron content in some fox spots.
• The presence of metal particles is consistent with the manufacturing processes used for hand-made and early machine-made papers.
• Some fox spots occur in patterns consistent with particles distributed during paper manufacture rather than biological growth.

The Combined Explanation

Current scientific consensus leans toward a combined explanation: metallic impurities in the paper create localized chemical conditions favorable to fungal growth, and the fungi then accelerate and extend the discoloration. This explains why foxing varies so much between papers — different manufacturing processes introduce different levels of metallic contamination, and different storage conditions promote or inhibit fungal activity.

Types and Appearance

Foxing varies considerably in appearance:

Light foxing — Scattered small spots, pale brown, barely noticeable unless you look closely. This is the most common form and the least damaging to value.

Heavy foxing — Dense concentrations of darker spots that significantly affect the visual appearance of the page. Heavy foxing can make text difficult to read and illustrations unpleasant to view.

Marginal foxing — Spots concentrated in the margins, away from text. Less objectionable than foxing that affects the text area.

Plate foxing — Foxing on illustration plates, often caused by the interaction between the plate paper and adjacent text pages. This is particularly concerning in illustrated books, where the plates are the primary attraction.

Tide-line foxing — Brown staining that follows the edge of a previous dampness intrusion, sometimes combined with scattered spots. Strictly speaking, this is water damage rather than true foxing, but the terms are sometimes conflated.

How Foxing Affects Book Value

The impact of foxing on value depends on severity, location, and the overall desirability of the book:

Minimal impact:

• Light, scattered foxing in an 18th-century or earlier book is expected and typically has modest impact on value.
• Foxing confined to preliminary leaves or endpapers is less concerning than foxing throughout the text.

Moderate impact:

• Foxing throughout a 19th-century first edition reduces value by 20–40% compared to a clean copy.
• Foxing on illustration plates in an illustrated book is more damaging than foxing on text pages.

Significant impact:

• Heavy foxing throughout a 20th-century book, where clean copies are available, can reduce value by 50% or more.
• Any foxing on a book described as “fine” or “near fine” contradicts the condition grade.

Context matters: Foxing in a book where clean copies are common (e.g., many Victorian novels) is a significant defect. Foxing in a book where virtually all surviving copies show it (e.g., many Keats first editions, printed on paper prone to foxing) is a recognized characteristic that buyers accept.

Can Foxing Be Removed?

Professional Conservation Treatment

Professional paper conservators can reduce or remove foxing through several methods:

Aqueous washing — Immersing the paper in deionized water (sometimes with mild bleaching agents) can lighten fox spots. This is one of the safest treatments when performed by a trained conservator, though it requires careful handling and may not be appropriate for all papers.

Chemical bleaching — Controlled application of mild bleaching agents (hydrogen peroxide, chloramine-T, or sodium borohydride) can lighten spots. This carries more risk than aqueous washing and must be performed by an experienced conservator.

Localized treatment — Individual spots can be treated with swabs or tiny applications of bleaching agents, allowing targeted treatment without subjecting the entire page to chemicals.

Important caveats:

• Treatment can lighten spots but rarely eliminates them entirely.
• Improperly performed bleaching can weaken paper, alter its color, or cause further damage over time.
• Treatment of foxing in rare books should only be performed by a qualified conservator, and the treatment should be disclosed to future buyers.

What NOT to Do

Do not attempt home remedies. Common advice found online — using household bleach, lemon juice, sunlight, or eraser treatments — is almost universally harmful. These methods damage paper, remove sizing, and can cause far worse problems than the foxing itself.

Do not iron foxed pages. Heat can set stains permanently and accelerate paper degradation.

Do not store affected books in sealed containers with desiccants in an attempt to “dry out” the fungus. Extreme dryness makes paper brittle.

Prevention

Environmental Control

Humidity is the single most important factor. Fox spots develop and spread in humid conditions. Maintaining relative humidity between 30–50% significantly reduces the risk of foxing and slows the progression of existing spots.

Temperature — Cooler storage temperatures slow both chemical oxidation and fungal growth. Room temperature (65–72°F / 18–22°C) is adequate for most collections; rare material benefits from cooler storage.

Air circulation — Stagnant air promotes moisture buildup and fungal growth. Ensure bookshelves are not pressed against exterior walls (which can be damp) and that air circulates around stored books.

Isolation

Books that show active foxing (spots that appear to be spreading) should be separated from clean books. While foxing is not directly “contagious,” the fungal spores that contribute to it can spread to adjacent volumes in humid conditions.

Paper Quality

Some papers are inherently more susceptible to foxing than others. Papers manufactured with high levels of metallic impurities, papers with high lignin content, and papers sized with organic materials are more vulnerable. This is why foxing is common in certain periods and publishers but rare in others.

Foxing in Condition Descriptions

When describing a book’s condition, foxing should be noted with specificity:

• “Occasional light foxing” — A few small, pale spots.
• “Scattered foxing to preliminaries” — Spots on front matter but not throughout.
• “Foxing throughout” — Spots present on most or all pages.
• “Heavy foxing to plates” — Significant spotting on illustrations.
• “Some foxing as typical of this title” — Acknowledges that the condition is normal for the specific edition.

Honest, specific foxing descriptions are expected from reputable dealers. Vague descriptions or omission of significant foxing is a red flag.