Glossary

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 various library materials and may be left in intentionally (as in certain sizings) or incidentally. Acids may also be introduced by migration from other materials or from atmospheric pollution. See also 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 (e.g.cotton and wood), if measures are taken during manufacture to eliminate active acid 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 atmospheric pollutants 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 or 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 materials to neutralize acids or as an alkaline reserve or buffer for the purpose of counteracting acids that may form in the future. A buffer may be added in manufacture or during the process of deacidification. While a number of chemicals may be used as buffers, the most common are magnesium carbonate and calcium carbonate.

Archival, Archivally Sound

A non-technical term suggesting a material or product is permanent or chemically stable and can be used safely for preservation purposes. The phrase is not quantifiable; no standards exist that describe how long an "archival" or "archivally sound" material will last.

Archival Polyester

A common name for the plastic polyethylene terephthalate. Its characteristics include transparency, colorlessness, and high tensile strength. Chemically inert, it is useful in preservation. Often used in sheet or film form to make folders, encapsulations and book jackets, its thickness is measured in mils. Common trade names are Mylar® and Melinex®.

Buffer

See Alkaline

Calcium Carbonate

An alkaline chemical used as a buffer in papers and boards.

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.

Chemical Stability

Not easily decomposed or modified chemically. This is a desirable characteristic for materials used in preservation, suggesting an ability to resist chemical degradation (such as paper embrittlement) over time and/or upon exposure to various conditions during use or storage. Other synonymous terms: inert, stable, chemically inert.

Conservation

Treatment of library or archive materials, works of art, or museum objects to stabilize them chemically or strengthen them physically, prolonging their life in their original form. See also Preservation.

Deacidification

A common term for a chemical treatment that neutralizes acid in a material such as paper and deposits an alkaline buffer to counteract future acid attack. Deacidification technically refers only to the neutralization of acids present at time of treatment, not to the deposit of a buffer. The term is being replaced with the more accurate phrase "neutralization and alkalization." While deacidification increases chemical stability of paper, it does not restore strength or flexibility to brittle materials. See also pH.

Encapsulation

Protective enclosure of papers and other flat objects. Involves placing the item between two sheets of transparent polyester film and sealing all edges. The item is thus supported and protected from the atmosphere, although it may deteriorate in the capsule. Because the item does not adhere to the polyester, it can be removed simply by cutting the edges of the polyester.

Fiberboard

Paperboard made of laminated sheets of heavily pressed fiber.

Friable

Easily crumbled.

Inert

See Chemical Stability

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 aid chemical degradation. It can be extensively removed during manufacture. No standards exist for the term "lignin-free" and more research is needed to determine the precise role of lignin in the durability and permanence of paper.

Mil

Unit of thickness equalling one thousandth of an inch (0.001").

Melinex®

See Archival Polyester

Mylar®

See Archival Polyester

Neutral

Having a pH of 7; neither acid nor alkaline.

pH

In chemistry, pH-the measure of the concentration of hydrogen ions in a solution-determines 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. See also Acid; Alkaline.

Permanence

Not quantifiable: the ability of a material to resist chemical deterioration. Permanent paper usually refers to durable alkaline paper manufactured according to ANSI Standard Z39, 48-1984 Permanence of Paper for Printed Library Materials. Even so-called permanent materials depend upon proper storage conditions for longevity. See also Chemical Stability.

Point

A unit of thickness of paper or board; one thousandth of an inch. E.g. 0.060" equals sixty points. See also Mil.

Polyethylene

A chemically inert, highly flexible, transparent or translucent plastic. Used in preservation to make sleeves for photographic materials, among many other uses.

Polypropylene

A stiff, heat-resistant, chemically inert plastic. Common uses in preservation include sleeves for photographic materials.

Polyvinyl Acetate

A plastic usually abbreviated as PVA. A colorless transparent material often used in adhesives, also referred to as PVA or PVA adhesive. While there are dozens or PVA adhesives, some are "internally plasticized" and are suitable for use in conservation, due mainly to greater chemical stability.

Polyvinyl Chloride (PVC)

A plastic, often abbreviated as PVC. It is not as chemically stable as some other plastics, and will emit hydrochloric acid (which, in turn, can damage library materials) as it deteriorates. It has no application in the preservation of books and paper

Preservation

Activities associated with maintaining library, archival, or museum materials for use, either in their original physical form or in some other format. Preservation is considered a broader term than Conservation. See also Conservation.

Pressboard

A tough, dense, highly glazed paperboard. Used where strength and stiffness are required of a relatively thin (e.g. .030") board. Almost as hard as a sheet of fiber board, it is commonly used for the covers of notebooks. See also Fiberboard.

Reversibility

Ability to undo a process of treatment with no change to the object. Reversibility is an important goal of conservation treatment, but it must be balanced with other treatment goals and options.

Sizings

Chemicals added to paper making it less absorbent so that inks applied will not bleed. Acidic sizings can be harmful and can cause paper to deteriorate, but some are not acidic and are expected to be more chemically stable.

Solid Board

A paper board made of the same material throughout. Distinct from combination board where two or more types of fiber stock are used in layers. See also Fiberboard and Pressboard.

UV Filter

A material used to filter the ultraviolet (UV) rays out of visible light. Ultraviolet radiation is potentially damaging to library, archival and museum objects. More is present in sunlight and fluorescent light than incandescent light. Removing UV radiation throughout library space can reduce the rate of deterioration of materials. A UV filtering material can be placed over windows, fluorescent light tubes, or glass used in framing and exhibition cases. Certain acrylic sheet materials have UV filtering properties built in.

Vinyl

The word vinyl is imprecisely used to refer to any of a number of plastics, many of which are not appropriate for use in preservation. For specific safe plastics, see Polyester, Polypropylene and Polyvinyl Acetate.

Reprinted with permission from ALCTS Newsletter, Vol. 1, No. 2, pgs. 14-15.