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Glossary of Preservation Terms

Acid

In chemistry, a substance capable of forming hydrogen ions when dissolved in water. Acids can weaken cellulose in paper, board, and cloth, leading to embrittlement. Acids may be introduced in the manufacture of library materials and may be left in intentionally (as in certain sizing) or incidentally. Acids may also be introduced by migration from other materials or from atmospheric pollution. Also see pH and Acid migration.

Acid-Free

In chemistry, materials that have a pH of 7.0 or higher. Sometimes used incorrectly as a synonym for alkaline or buffered. Such materials may be produced from virtually any cellulose fiber source (cotton and wood among others), if measures are taken during manufacture to eliminate active acid from the pulp. However free of acid a paper or board may be immediately after manufacture, over time the presence of residual chlorine from bleaching, aluminum sulfate from sizing, or pollutants in the atmosphere may lead to the formation of acid unless the paper or board has been buffered with an alkaline substance.

Acid Migration

The transfer of acid from an acidic material to a less acidic of pH neutral material. This may occur directly, when the two materials are in intimate contact. For instance, acid may migrate from boards, end papers, and protective tissues, as well as the paper covers of books and pamphlets, to the less acidic paper of the text.

Alkaline

Alkaline substances have a pH over 7.0. They may be added to a material to neutralize acids or as an alkaline reserve or buffer for the purpose of counter-acting acids that may form in the future. A buffer may be added during manufacture of during the process of deacidification. While a number of chemicals may be used as buffers, the most common are magnesium carbonate and calcium carbonate.

Alpha Cellulose

A form of cellulose derived from cotton. The presence of alpha cellulose in paper or board is one indication of its stability or longevity. Non-cellulosic components of wood are believed to contribute to the degradation of paper and board.

Buffer

See Alkaline.

Cellulose

The chief constituent of the cell walls of all plants. Also, the chief constituent of many fibrous plant products, including paper and some cloth.

Conservation

The treatment of library materials to stabilize them chemically or strengthen them physically, sustaining their survival as long as possible in their original form. Also see Preservation.

Deacidification

A common term for a chemical treatment that neutralized acid in a material such as paper and deposits an alkaline buffer to counteract future acid attack. The term is being slowly replaced with the more accurate phrase "neutralization and alkalization". While deacidification increases the chemical stability of paper, it does not restore strength or flexibility to brittle materials.

Durability

The degree to which a material retains its physical properties while subjected to stress, such as heavy use. To say that a material is durable suggests that it has a high initial strength.

Fiber Content

A statement of types and percentages of fibers used in the manufacture of a paper, board, or cloth. Important because the quality of the fiber significantly affects both the durability and chemical stability of the material.

Lignin

A component of the cell walls of plants that occurs naturally, along with cellulose. Lignin is largely responsible for the strength and rigidity of plants, but its presence in paper and board is believed to contribute to chemical degradation. It can be, to a large extent, removed during manufacture. No standards exist for the term "lignin-free" and additional research is needed to determine the precise role of lignin in the durability and permanence of paper.

Neutral

Having a pH of 7; neither acid nor alkaline.

pH

In chemistry, pH is a measure of the concentration of hydrogen ions in a solution, which is a measure of acidity or alkalinity. The pH scale runs from 0 to 14, and each number indicates a ten-fold increase. Seven is pH neutral; numbers below 7 indicate increasing acidity, with 1 being most acid. Numbers above 7 indicate increasing alkalinity, with 14 being most alkaline. Paper with a pH below 5 is considered highly acidic. Buffered storage materials typically have a pH between 7 and 9.

Preservation

Activities associated with maintaining library, archival, or museum materials for use, either in their original physical form or in some other format.

This information was taken from ALCTS Newsletter, Vol. 1, No. 2, pp 14–15.

11/15/03