Foxing is a term describing the age-related spots and browning seen on vintage paper document

Document

The term document has multiple meanings in ordinary language and in scholarship. WordNet 3.1. lists four meanings :* document, written document, papers...

s such as book

Book

A book is a set or collection of written, printed, illustrated, or blank sheets, made of hot lava, paper, parchment, or other materials, usually fastened together to hinge at one side. A single sheet within a book is called a leaf or leaflet, and each side of a leaf is called a page...

s, postage stamp

Postage stamp

A postage stamp is a small piece of paper that is purchased and displayed on an item of mail as evidence of payment of postage. Typically, stamps are made from special paper, with a national designation and denomination on the face, and a gum adhesive on the reverse side...

s, certificates, and so forth. The name may derive from the fox

Red Fox

The red fox is the largest of the true foxes, as well as being the most geographically spread member of the Carnivora, being distributed across the entire northern hemisphere from the Arctic Circle to North Africa, Central America, and the steppes of Asia...

-like reddish-brown color of the stains, or the rust chemical ferric oxide which may be involved. Paper so affected is said to be "foxed."

Although unsightly and a negative factor in the value of the paper item for collectors, foxing does not affect the actual integrity of the paper.

Foxing also occurs in biological study skins or specimens, as an effect of chemical reactions or mold

Mold

Molds are fungi that grow in the form of multicellular filaments called hyphae. Molds are not considered to be microbes but microscopic fungi that grow as single cells called yeasts...

 on melanin

Melanin

Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...

.

Other causes of age-related paper deterioration include destruction of the lignin

Lignin

Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...

 by sunlight and absorbed atmospheric pollution, typically causing the paper to go brown and crumble at the edges, and acid-related damage to cheap paper such as newsprint

Newsprint

Newsprint is a low-cost, non-archival paper most commonly used to print newspapers, and other publications and advertising material. It usually has an off-white cast and distinctive feel. It is designed for use in printing presses that employ a long web of paper rather than individual sheets of...

, which is manufactured without neutralising acidic contaminants.

Causes of foxing

The causes of foxing are not well understood. One theory is that foxing is caused by a fungal growth on the paper

Paper

Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....

. Another theory is that foxing is caused by the effect on certain paper

Paper

Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....

s of the oxidation of iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

, copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

, or other substances in the pulp

Wood pulp

Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fibre crops or waste paper. Wood pulp is the most common raw material in papermaking.-History:...

 or rag from which the paper was made. It is possible that multiple factors are involved.

High humidity may contribute to foxing.

Repairing foxed documents

There are products available which were specifically designed to remove foxing. The problem with using proprietary bleaches to remove foxing is that they invariably affect the integrity of the paper and the paper has to be subsequently resized

Sizing

Sizing or size is any one of numerous specific substances that is applied to or incorporated in other material, especially papers and textiles, to act as a protecting filler or glaze....

.

Using laser-based techniques to remove foxing stains from old paper is a potential solution to the problem. The use of lasers however, at longer wavelengths, is usually accompanied by side effects, since the affected area requires higher laser energieshttp://www.eie.gr/nhrf/institutes/tpci/researchteams/pn/pn-services-en.html to be cleaned.

Depending on how valuable one's print or map is, one could try lightly dabbing 3% hydrogen peroxide

Hydrogen peroxide

Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...

 onto the affected area using a cotton swab

Cotton swab

Cotton swabs or cotton buds or ear buds consist of a small wad of cotton wrapped around one or both ends of a short rod, usually made of either wood, rolled paper, or plastic...

 or cotton bud. This process is effective but one should test the paper in a less critical area first. It doesn't take much and one should not soak the spots; the hydrogen peroxide will bleach the ink just as it will bleach the foxing. Patience and repeated applications are best. Scan a yellowed or foxed page using the text-enhanced mode for best scanning results.

Foxing in biological specimens

It is generally not advisable to repair study specimens, except perhaps for mechanical damage. Type specimens should, if by any means possible, not be altered in any way. If foxing affects the study value of a specimen (e.g. in bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

 or mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

 skins or in insects, where it might affect diagnostic coloration), this might rather be remarked on the specimen label. Color standards can provide a means of documenting coloration before or in the early stages of foxing.