Glossary of terms

Acid, Acid-free, Acid Migration , Acrylic, Alkaline , Alpha cellulose , Buckram , Buffer , Calcium Carbonate , Cellulose , Chemical Stability , Conservation , Deacidification , Deckled Edge, Encapsulation , Fibre content , Fibreboard , Lamination , Lignin , Micron, Mylar® & Melinex®, Neutral , Permanence , PlexiGlas® , Point , Polyester , Polyethylene , Polypropylene , Polyvinyl Acetate (PVA) , Polyvinyl Chloride (PVC) , Preservation , Pressboard , Reversibility, RH, Sizings, Solid Board , Stability, UV Filter, Vinyl

Acid

In chemistry, a substance capable of forming hydrogen ions when disolved 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 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. Some-times 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 or pH neutral material. This may occur directly, when the two materials are in intimate contact. For instance, acid may migrate from boards, endpapers, and protective tissues, as well as the paper covers of books and pamphlets, to the less acidic paper of the text.

Acrylic

A plastic noted for transparency, light weight, weather resistance, color fastness and rigidity. In addition to these qualities, acrylics are important in preservation because of their stability, or resistance to chemical change over time, a characteristic not common to all plastics. Acrylics are available in sheets, films, and resin adhesives. Some common trade names for the sheet form are: Perspex®, Lucite® and PlexiGlas®.

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 counteracting acids that may form in the future. A buffer may be added during 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.

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.

Buckram

Commonly used to cover books, buckram cloth is a hardwearing cotton or linen cloth. It can withstand heavy use and is resistant to tearing, it is also water resistant and can be wiped clean.

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 otherwise modified chemically. This is a desirable characteristic for materials used in preservation, since it suggests an ability to resist chemical degradation (such as the embrittlement of paper), over time and/or upon exposure to various conditions during use or storage. Other terms used loosely as synonyms: inert, stable, chemically inert.

Conservation

The treatment of library or archive materials, works of art, or museum objects to stabilize them chemically or strengthen them physic-ally, sustaining their survival as long as possible 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 the time of treatment, not to the deposit of a buffer. For this reason, 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. See also pH.

Deckled Edge

A deckled edge is the feathered or uneven edge produced in traditional/hand-made paper making methods where the edges are shuttered with a 'deckle'. The deckled edge is formed of the fibres from the slurry which have seeped under the deckle frame. In modern paper making, deckled edges are generally machine created.

Encapsulation

A form of protective enclosure for papers and other flat objects; involves placing the item be-tween two sheets of transparent polyester film that are subsequently sealed around all edges. The object is thus physically supported and protected from the atmosphere, although it may continue to deteriorate in the capsule. Because the object is not adhered to the polyester, it can be removed simply by cutting one or more edges of the polyester.

Fibre content

A statement of the 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.

Fibreboard

Paperboard made of laminated sheets of heavily pressed fiber. Inert See Chemical Stability.

Lamination

A process of reinforcing fragile paper, usually with thin, translucent or transparent sheets. Some forms of lamination are considered unacceptable as conservation methods because of potential damage from high heat and pressure during application, instability of the lamination materials, or difficulty in removing the laminated item, especially long after the treatment was performed.

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.

Micron

Unit of thickness one mm is equal to 1000 micron.

Mylar® & Melinex®

Brand names for archival polyester produced by DuPont. See Polyester.

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. See also Acid; Alkaline.

Permanence

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

PlexiGlas®

Trade name for acrylic sheet material made by Rohm and Haas. See Acrylic for other trade names.

Point

A unit of thickness of paper or board; one thousandth of an inch. For example, .060” equals sixty points. See also Micron.

Polyester

A common name for the plastic polyethylene terephthalate. Its characteristics include transparency, colorlessness, and high tensile strength. In addition, it is useful in preservation because it is very chemically stable. Commonly used in sheet or film form to make folders, encapsulations and book jackets. Its thickness is often measured in mils. Common trade names are Mylar® by DuPont and Melinex® .

Polyethylene

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

Polypropylene

A stiff, heat resistant, chemically stable plastic. Common uses in preservation: sleeves for 35mm slides or films, containers.

Polyvinyl Acetate (PVA)

A plastic usually abbreviated as PVA. A colourless transparent solid, it is usually used in adhesives, which are themselves also referred to as PVA or PVA adhesive. There are dozens of PVA adhesives, some are “internally plasticized’’ and are suitable for use in conservation, due to greater chemical stability among other qualities.

Polyvinyl Chloride (PVC)

A plastic, often abbreviated as PVC. It is not as chemically stable as some other plastics, since it can emit hydrochloric acid (which in turn can damage library materials) as it deteriorates, and therefore has limited application in the preservation of books and paper. Some plastics called vinyl may be polyvinyl chloride.

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 Conservation.

Pressboard

A tough, dense, highly glazed paperboard, used where strength and stiffness are required of a relatively thin (e.g. .030”) board. It is almost as hard as a sheet of fiberboard, and is commonly used for the covers of notebooks. See also Solid board, Fibreboard.

Reversibility

Ability to undo a process or 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.

RH

Stands for 'Relative Humidity' and is important when setting up storage environment.

Sizings

Chemicals added to paper that make 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 paperboard made of the same material throughout. Distinct from a combination board where two or more types of fiber stock are used, in layers. See also Fibreboard, Pressboard.

Stability

See Chemical stability.

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 and more is present in sunlight and fluorescent light than in incandescent light. Removing UV radiation from storage, use, and exhibition spaces can reduce the rate of deterioration of library materials stored there. Usually a UV filtering material is placed over windows or fluorescent light tubes, or over glass used in framing, or in 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, Polyvinyl acetate, Acrylic.