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 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, aluminium 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, 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 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.
Archival (Archival Quality) – This non-technical term suggests that a material or product is permanent, durable or chemically stable, and that it can therefore safely be used for preservation purposes. The phrase is not quantifiable; no standards exist that describe how long an ‘archival’ or ‘archival quality’ material will last.
Buffering – Paper and paperboard products are divided between buffered and unbuffered. Calcium carbonate is the preferred buffering agent of preservation professionals. The buffering agent helps neutralize acids in the environment and helps to prevent those acids from attacking collections. Because of concerns over the affect of buffering agents on certain animal-based products such as wool, leather and silk, hair, feathers, bone etc., unbuffered storage products are recommended for these materials, and also for certain rare photographic collections including dye transfer and cyanotypes. Note: Unbuffered materials can absorb acids from the environment and can, eventually become acidic themselves.
Calcium Carbonate – An alkaline chemical used as a buffer in papers and boards.
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.
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 fibre significantly affects both the durability and chemical stability of the material.
Grain Direction – This represents the orientation of fibres in paper. Paper has a natural tendency to fold ‘with the grain’ usually making it easy to determine the grain direction you are working with. Grain direction can be considered either short or long, depending on whether it runs parallel to the long or short side of the paper dimensions.
Inert – See chemical stability.
Lignin (Lignin-free) – Lignin is a naturally occurring substance found in plants that provides rigidity. In some circles, lignin is thought to contribute to the early degradation of paper and is often removed during the pulping process to create higher-grade paper.
Micron – Unit of thickness one mm is equal to 1000 micron.
Mylar® & Melinex® – 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.
pH (presence of Hydrogen) – In chemistry, pH is a measurement of the concentration of Hydrogen ions, which is a measure of acidity or alkalinity. The pH scale runs from 1 to 14, with 7 being pH neutral; numbers below 7 indicate increasing acidity with 1 being most acidic, numbers above 7 indicate increasing alkalinity, with 14 being most alkaline. Each number away from 7 represents a ten-fold increase. Paper with a pH below 5 is considered highly acidic. Buffered storage materials typically have a pH between 7 and 9.
Photo Activity Test (PAT) – The PAT is an accelerated aging test that predicts the affects a material may have on photographic images. In essence, it predicts the type of interaction between an enclosures and photographic materials, and determines if any of the enclosures’ components, including adhesives, inks, paper and plastic, will adversely effect a photograph, negative, or other photographic materials.
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.
Point – A unit of thickness of paper or board. One point equals one thousandth of an inch. For example, 0.060” equals 60 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 soft, 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.
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.
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.
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.