This glossary defines some of the most common technical words used in the literature of library and archive preservation. Where possible, non-technical, easily understood terms have been used.

You are likely to encounter alternative definitions of some of these terms in the conservation literature as definitions change and are interpreted differently in various areas of conservation. You will also find that some terms are used differently in some countries; in different regions in the same country; and even between professionals in the same organisation.

The glossary is derived from several sources including:

  • Glossary of basic archival and library conservation terms, ICA Handbooks series, volume 4, Saur, Munich, 1988
  • Glossary of selected preservation terms, ALCTS Newsletter, vol 1 no 2, 1990 pp14-15

However, other preservation glossaries have also been consulted and adapted. Since some terms are defined in similar ways in many glossaries, it is difficult to acknowledge the originator of many terms given in this glossary.

For specific definitions of book related terms, the online glossary in CoOL by M Roberts and D Etherington should be consulted. The Conservation Online web site CoOL has a general listing of other glossaries, word lists etc at which is particularly useful for electronic and digital preservation terms.

In the glossary entries, terms in green are linked to their own glossary entry.

Copyright Wendy Smith 1992-2003. E-mail address:

Conservation Resources gratefully acknowledges the support of Wendy Smith of the Australian Library and Information Association

Acid (adj. acidic)

In chemistry, a material that can form hydrogen (H+) ions when dissolved in water. Acids damage cellulose in paper, board and cloth by weakening or breaking molecular bonds which leads to embrittlement. Acidic materials can be introduced during the manufacture of library and archive materials, or may be present in the raw material. Acids can also be introduced by migration or from atmospheric pollution. Acids can be neutralised by an alkali to form a salt.

Acid deterioration

The weakening of paper or board structure by an acid, through hydrolysis or other means. This results in breaking down the chain length of the material with a subsequent loss of strength. This can become so severe that the paper may have almost no residual strength left. It is then said to be brittle.

Acid free

In chemistry, materials that have a pH of 7(neutral) or higher (alkaline). Acid free paper is often alkaline buffered. Since cellulose is damaged by acids, acid free materials are desirable in library and archive preservation.

Acid migration

The transfer of acid from an acidic material to a less acidic, neutral, or alkaline material. This may occur when two materials are in direct contact or indirectly by vapour transfer. It can cause staining, weakening and embrittlement. The actual mechanisms of acid migration are not well understood, and the term is sometimes erroneously applied to any transfer of a stain to an adjacent surface.


A plastic material noted for its transparency, weather resistance and colour fastness. Acrylics are important in preservation because of their stability and resistance to chemical change. Acrylics are available in sheets, films and resin adhesives. Some common trade names for sheet acrylics are Perspex, Lucite and Plexiglas. Ultraviolet absorbing acrylic sheet is used in preference to glass for glazing framed materials because it is less likely to break and the additional ultraviolet absorbers protect the framed objects from light damage.


A substance used to join two materials together, by chemical or mechanical action. Generally applied as a liquid, or as a solid activated by heat or pressure. A desirable characteristic of adhesives used in conservation is reversibility.

Adhesive tape

Paper or fabric tape with an adhesive layer applied. The adhesive layer is generally activated by pressure, or by the application of heat or water. Ordinary pressure sensitive or 'sticky' tapes should not be used for materials intended for long term preservation, since the adhesive can degrade and yellow and the adhesive residues can become impossible to remove. Some archival adhesive tapes are safer to use, but caution should still be exercised especially on very valuable materials.

Alkali (adj: alkaline)

In chemistry, a material that can form hydroxyl (OH-) ions when dissolved in water. Alkaline materials are sometimes added to conservation materials to neutralise acids or to provide an alkaline reserve or buffer for the purpose of counteracting acids which may form in the future. While a number of chemicals may be used as alkaline buffers, the most common ones used in paper conservation are magnesium carbonate or calcium carbonate. Alkalis can be neutralised by an acid to form a salt.

Alum / rosin size

Chemicals commonly used to size paper. Alum/rosin sizes were used extensively in the past, and have contributed significantly to the brittle book problem because they leave an acidic reserve in the paper.

Ambient conditions

The existing conditions of temperature and humidity in any building or room

Archival quality

A term suggesting that a material, product or process is durable and/or chemically stable; that it has a long life; and can therefore can be used for preservation purposes. The phrase is not quantifiable; no standards exist that describe how long an 'archival' material will last. The word 'permanent' is sometimes used to mean the same thing. Some organisations, for example ANSI, are now using the term life expectancy (LE) - LE = 100 years, LE = 500 years etc.


Application of an additional layer to an item to provide support. Sometimes called lining. Backing is a conservation treatment used on weakened sheet paper items.


The cosmetic whitening or reduction of coloured substances in an object by the chemical action of an oxidising or reducing agent. The process is likely to weaken paper, and is rarely recommended to be used in library and archive preservation.


The loss or spreading of colour when coloured paper or ink comes in contact with water or other solutions. Even very high humidity can trigger bleeding in some materials, including digital images printed on some bubblejet ‘photographic’ papers.


The joining together of pages of a book to form a solid block. Likely effect of water damage or high humidity on some coated papers. Blocking is less likely to be a problem with modern coated papers.

Blotting paper

Soft, unsized paper or board used to absorb moisture. Blotting paper used in conservation should not be coloured.

Board, cardboard

A general term for various pulped or laminated fibrous materials made into large, flat sheets, thicker and more rigid than paper. Cardboard is the term in more general use.

Bone folder

A very useful small smooth, flat tool made of animal bone or plastic and used to remove air bubbles, smooth, flatten crease or ensure adhesion between two materials. Bone folders are typically 150-200mm long, 2 or 3 mm thick, with one pointed and one rounded end.

Brittle / brittleness

A property or condition of paper or board that causes failure of the material when it is deformed by bending. Paper is said to be brittle when a corner will not withstand two complete double folds.

Buckling / cockling

The warping and twisting in several directions of, for example, the covers of a book; a puckered effect caused by excessive heat or moisture. Wet paper or board will only dry flat if subjected to some force or pressure, otherwise it will remain crumpled.

Buffer / buffering

A process sometimes used in conjunction with deacidification or during manufacture, when an alkaline material is deposited in paper in order to neutralise future potential acidity

Calcium carbonate

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


Chemically, a complex carbohydrate. Cellulose is the chief constituent of the cell walls of plants, and consequently the chief constituent of many fibrous plant products such as paper and board, and cotton, linen and rayon cloth. Traditional Western plants providing cellulose for paper were cotton and linen ('rag' paper). Wood is the major source of papermaking fibres today. The quality of wood pulp papers can vary from very high to very low, depending both on the methods of extraction of the cellulose fibres and manufacturing methods.

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 paper embrittlement, over time and/or exposure to varying conditions during use or storage. Sometimes described as chemically inert.

Coated paper

Paper with a surface coating (adhesives, clay or other pigments etc) that is added to improve its finish in terms of printability, smoothness or opacity. Coated papers usually have a glossy appearance and are sometimes called 'art papers’. Older clay coated papers have a tendency to block when they are exposed to high relative humidity or become wet.


The use of procedures to preserve and repair the physical structure of an item. All processes ideally should be reversible.


A person professionally responsible for the physical preservation of collection items in order to retain and maintain their evidential or informational content.


A common term for a chemical treatment that neutralises acid in a material such as paper, and that may deposit an alkaline buffer to counteract future acid attack. While deacidification may increase the chemical stability of paper, it does not restore strength or flexibility to brittle materials.

Dehumidifier (adj: dehumidification)

Equipment that reduces the humidity in the atmosphere by the use of refrigeration, desiccants or absorbent drying agents.


Damage caused to an item by physical, chemical or biological means.

Diazo film

A type of microform in which the active component is a light sensitive diazo dye. It is recommended for duplication and use copies of microfilm since it is less expensive than silver halide film. However, it is not considered archival and original microfilming should be undertaken using silver halide film

Disaster plan

A document setting out procedures to be followed by an organisation to prevent or minimise the risk of a disaster occurring, and to describe actions to be taken should a disaster occur. Such a plan will normally include provisions for the prevention of a disaster; salvage procedures in case a disaster should occur; and replacement/restoration measures to be taken. More correctly should be called a disaster preparedness plan.


The degree to which a material retains its physical properties while subjected to stress: such as heavy use, or adverse environmental conditions. To say a material is durable suggests that it has high initial strength, and will last a long time under normal conditions of use.


A recommended form of protective enclosure for paper and other flat objects. It involves placing the item between two sheets (or one folded sheet) of clear plastic film (usually polyester), that are subsequently sealed with adhesive tape or by heat welding or sewing around the edges. The encapsulated object is thus physically supported and protected from the atmosphere, although it may continue to deteriorate within the package. A sheet of buffered paper or board is sometimes included. The object can simply be removed by cutting one or more edges of the plastic film. If the objet need to be removed frequently then not all edges need be sealed. An alternative form of encapsulation sees the back sheet of polyester replaced by a rigid sheet of cardboard or plastic. Encapsulation should not be confused with lamination.

Environmental control

The maintenance of safe levels of light exposure, humidity, temperature, air pollution, air movement and dirt inside a building where collections are housed.


A reproduction or copy of an original work that is similar in appearance to the original.

Fore edge

The front edge of a book; the edge of a book that opens; the side opposite the spine.

Form / format

The physical medium in which information is recorded or carried - paper, microfilm, photograph, computer disc, machine- readable record.


Discolouration on paper, generally in the form of random rust coloured spots. Believed to be caused by one or more of the following; fungus or mould, impurities in manufacture, high humidity or dampness, airborne acids. The removal of foxing is not generally recommended in library and archive preservation since methods of removing foxing almost always will cause further damage to the object.

Freeze drying (vacuum)

A method of removing water from wet books or other material. The material is first frozen and then placed in a high vacuum, so that the water (ice) vaporises in the vacuum (sublimes) without passing through the liquid state.


The exposure of materials to the vapour of a volatile substance or toxic chemical in a closed container or chamber in order to destroy fungi and/or insects or animal pests.

Fungus / fungi / mould

Fungi are types of microscopic plant materials that are very numerous and occur in many different forms. Their spores, or reproductive bodies are everywhere and await only proper conditions of moisture and temperature to germinate, grow and reproduce. Fungi cause staining and weakening of most library and archive materials. Keeping the relative humidity below 70-80% and providing good air movement is the best way to control the growth of mould.


A substance capable of destroying or preventing the growth of fungi. Fungicides do not provide any residual protection from future mould growth.


An adhesive made from protein derived from the collagen in animal products such as hides and bones. Animal glues become yellow and brittle with age.


In machine made paper and board, the direction in which the fibres predominantly lie. Grain direction needs careful consideration in book production, bookbinding and paper conservation treatments.

Groundwood paper

See paper


The top of a book as it sits upright

Hot melt adhesive

An adhesive that is liquid when hot but solid at room temperature. Hot melt adhesives were extensively used in paperback bindings. They are generally inflexible and can become brittle and yellow as they age. Pages become easily detached when this happens.


The moisture in the air. See also relative humidity


A chemical action involving water - decomposition in which a compound is split into other compounds by taking up water.


See psychrometer


See thermohygrograph


See chemical stability.


A technique used to repair and strengthen documents, whereby they are adhered into a frame of paper whose inner dimensions are slightly smaller than the document itself.


A pesticide used to kill insect life.


A process of using sheets of paper or other material to separate items. The use of buffered paper is often recommended when interleaving acidic materials.

Intrinsic value

Historic or other value of an item that means it must be retained and preserved in its original form - the value that the item has beyond the value of the recorded information contained in it.


A process of reinforcing fragile sheet material, usually using transparent or translucent sheets of plastic or paper. Some forms of lamination such as those using cellulose acetate are considered unacceptable as preservation methods because of high heat and pressure during application, instability of lamination materials or difficulty in removing lamination from the item, especially a long time after the lamination was performed. Lamination should never be used on items of long term value. Commercial laminating films are only suitable for material of short term or ephemeral value.


A very small portion of the electromagnetic spectrum of radiation, covering the wavelengths from approximately 400 - 700 nanometres(nm) for visible light, and 300-400 nm for ultraviolet light. The energy of light radiation can damage collection materials by causing photochemical damage. The amount of damage is proportional both to the intensity and the duration of exposure to light.


A component of the cell walls of plants. Lignin is largely responsible for the strength and rigidity of plants, but its excessive presence in paper and board is believed to contribute to chemical degradation. There can be large amounts of lignin present in pulp made from wood: it is not removed in the production of mechanical pulp, but it can be removed almost completely in chemical papermaking processes to produce ‘archival’ quality paper.

Medium / media

The material on which information is recorded. Sometimes also refers to the actual material used to record the image.


A sheet of flat photographic film, usually 4 x 6 inches in size, containing rows of images with an eye legible title.


Photographic film used in micrographics, usually in roll form 35mm or 16mm wide. 35mm format is preferred for preservation microfilming.


A term to describe both microfilm and microfiche formats.


See also microform / microfilm / microfiche. The use of photographic processes to produce very small images of original materials. Types of microformat include the above.

Mould / mold

See fungus.


See polyester

Neutral (adj: neutralise)

In chemical terms, having a pH of 7; neither acid nor alkaline


A chemical process where a compound combines with oxygen to form a different compound.


A short book composed typically of less than 100 pages and usually given only a paper cover.


Paper is a matted or felted sheet of predominantly cellulose fibres, formed on a fine screen from a water suspension of the fibres. Papers can be hand or machine made. Traditional Western papers were made from cotton or linen rags. Modern papers are made from wood fibres. The type of wood pulp used to make the paper will influence its expected lifespan - alkaline papers are usually more stable than acidic papers; groundwood papers contain high amounts of lignin and have a short lifespan. Chemical wood pulp papers can be made to very high standards of quality. Japanese or oriental papers are made by traditional methods from a variety of plant fibres - they are valued for their properties of flexibility, strength and (sometimes) permanence.


An adhesive made from starch or flour such as rice or wheat, generally prepared by heating together a mixture of starch and water and subsequently cooling the resulting product. This in turn may be diluted with water to produce the required texture. PVA can be added to the paste to give an adhesive with fast drying and strength where long term reversibility is not required.


The stability of a material and its ability to resist chemical deterioration - not a quantifiable term.


See archival. A permanent paper is one that conforms to an agreed standard, is usually acid free and made to resist changes to a greater degree than is usual in other papers.


In chemistry, pH is a measure of the concentration of hydrogen ions in solution, which indicates the acidity or alkalinity of the solution. The pH scale runs from 0 to 14, with each number indicating a 10 times differential. 7 is pH neutral, numbers below 7 indicate increasing acidity and above 7 increasing alkalinity. Alkaline buffered storage materials used in libraries and archives typically have a pH above 7 and below 9.

Phase box

A simple, economical ‘4 flap’ wrap-around box designed to provide an acceptable degree of protection to its contents without undertaking full conservation treatment. Initially developed to provide intermediate protection to materials awaiting further treatment, but now used as a preservation procedure in its own right.

Phased preservation

Collections maintenance activities such as the provision of simple boxes, folders or protective enclosures, rehousing and other preventive preservation procedures, while establishing priorities for future treatment.

Photochemical degradation

Damage caused or increased by exposure to light.

Photographic Activity Test.

To ensure its suitability for the storage of photographic materials, ProLong® Archival Paper passes the Photographic Activity Test ISO 14523:1999(E).

The Photographic Activity Test (PAT) was developed by the Image Permanence Institute in the USA to test the quality of photographic storage materials.

Materials that pass the PAT provide the highest degree of protection for photographs. As such, ProLong® Archival Paper is safe to use in direct contact with stored or displayed photographs.


A chemical added to another material to give it increased flexibility. In some plastics such as PVC, plasticisers leach out in time and leave the material brittle. Adhesives for use in preservation should be 'internally plasticised'.


A unit of measuring the thickness of paper or board. One point equals 1/1000th on an inch, sometimes referred to as a ‘mil’. Metric based measurements are based on the micron. 4 mil is equivalent to 100 microns.


The common name for the plastic polyethylene terephthalate. Its characteristics include transparency, lack of colour, high tensile strength, and chemical stability (when made with no coatings or additives). Used in sheet or film form to make folders, encapsulations, protective pockets and book jackets. Trade names include Mylar and Archival Polyester. Used in web form ('Reemay') to support paper during wet treatments, and as a relatively non-stick surface through which moisture can pass during mending, drying etc.

Polyethylene (PE)

In its pure form, a chemically stable plastic material. Used in film form for a variety of purposes, including film negative holders and page protectors. A cheaper alternative to polyester film.


In chemistry, a large organic compound made up of a series of smaller repeating units joined together by chemical bonds in a regular way.

Polypropylene (PP)

In its pure form, a chemically stable plastic material. Used in film form as for polyethylene. Used in sheet form for boxes, folders and such. Cheaper alternatives to polyester film and archival cardboards.

Polyvinylacetate (PVA)

A plastic usually abbreviated as PVA. A colourless, transparent solid, it is used in adhesives which are themselves also referred to as PVA or PVA adhesive. There are many varieties of PVA adhesives. The types referred to as 'internally plasticised' have greater chemical stability, and are preferred for use in preservation. PVA adhesives are often used in an emulsion form such as the commonly used woodworking or craft 'white glue'. They have a milk-like appearance, but dry clear.

Polyvinylchloride (PVC)

A plastic usually abbreviated as PVC, or sometimes 'vinyl'. Not as chemically stable as some other plastics, and can break down to emit acid components that damage susceptible materials such as paper. Added chemicals called plasticisers are used to make PVC more flexible. These also damage library and archive materials.

The Polyweld process

It is important that the sealing of the polyester is as permanent as the polyester itself, which is why each product is hand-made on the patented Polyweld machine. Polyweld is a method of sealing the edge of the polyester sheets without using any adhesives, solvents or additives of any kind. Through heat, this method 're-extrudes' the polyester to provide a seal that is as strong as the original material, with a unique smooth, rolled edge.


Activities associated with maintaining library, archival or museum materials for use, either in original physical form or in some other format. Preservation is a broader term than conservation: conservation activities form part of a total preservation program. Preservation includes both activities taken to repair or treat damaged materials (retrospective) and activities taken to prevent or delay material becoming damaged (preventive preservation).

Pressure sensitive tape

Sometimes called 'sticky' tape. An adhesive tape that attaches to a surface when pressure is applied. The adhesive frequently degrades leaving a brown residue that stains and makes paper brittle. Not recommended for materials intended for long-term preservation. Some archival adhesive tapes are safer to use, but caution should still be exercised especially on very valuable materials.

Preventive preservation

All the management activities undertaken to prevent or delay material becoming damaged, including control and monitoring of the environment; disaster response planning; and staff and user education

Psychrometer / sling psychrometer

A simple instrument used to measure temperature and relative humidity. Sling psychrometers are relatively inexpensive to purchase compared to dataloggers and thermohygrograph, but are very accurate when used properly.


Fibrous materials, generally from plant materials including trees, used in the manufacture of paper or board. Groundwood pulp, which is produced by mechanical methods, contains high amounts of lignin and has poor durability. Groundwood pulp is typically used to produce newsprint, which is not intended to have a long expectancy. Chemical pulp has a considerable amount of non-cellulosic material including lignin removed during processing, and the resultant paper has a higher durability than groundwood paper. Permanent papers and boards can be made from chemical pulp.


See polyvinylacetate.


See polyvinylchloride.


The process of converting information from one form to another - see also reprography andsurrogate. Reformatting is usually undertaken when the long-term survival of information can no longer be guaranteed in its current format. Reformatting or information migration is increasingly being used for electronic and digital information as existing hardware and software becomes obsolete.

Relative humidity (RH)

The percentage of moisture contained in air as compared with that required to completely saturate it at a given temperature. A low relative humidity of around 40% is considered ideal for paper storage, but is very difficult to achieve in the humid tropics. Mould growth becomes a serious problem above 70% relative humidity.


A range of processes used to copy or produce reproductions of items by optical or photographic means - including photography, photocopying, and microfilming.


See facsimile. A copy of an original item, not necessarily in the same form.


The ability to undo a process or treatment with no or minimal change to the object. Reversibility is an important goal of conservation treatments, but it must be balanced against other treatment goals or options. Full and total reversibility is an ideal that is impossible to achieve.

Silver halide film

Photographic film in which the light sensitive ingredient is a silver halide emulsion. Properly processed and stored, silver halide film can be considered archival, and should be used for master microform production.

Size ( sizing)

Chemicals added to paper and board during manufacture to make it less absorbent, so that inks will not bleed, and the image will have better definition. Sizing can also be used to strengthen weak papers. Rosins, gelatin, starches and synthetic resins are used as sizing agents. Sizes used in permanent papers are alkaline.


A well fitting open-fronted case into which a book may be slipped or pushed for protection, leaving the spine displayed.


The back edge of a book; opposite to the fore-edge


A copy of the information content of an original item in another medium, usually one that is more durable. See also reproduction and facsimile.

Thermohygrograph (THG)

A piece of equipment that records temperature (thermo) and relative humidity (hygro). Sometimes called a hygrothermograph. Usually the results are plotted instantaneously on a chart recorder. To be effective thermohygrographs need to be well maintained and frequently calibrated against a standard measuring instrument such as a sling psychrometer. Automatic computer-based dataloggers are preferable, being cheaper and more versatile than thermohygrographs.

Tipping in

The attachment of one leaf or sheet of paper to another by means of a narrow strip of adhesive along one edge of the leaf.

Ultraviolet light (UV)

Light having a shorter wavelength and higher energy than visible light. Ultraviolet light is potentially very damaging to library, archive and museum objects. Removing UV light can reduce the rate of deterioration. Certain acrylic sheets have UV filtering chemicals built into them.

UV filter

A material used to filter the ultraviolet rays out of visible light.

Vesicular film

A type of microform in which the image consists of tiny bubbles or vesicles in a polymer binder and is developed by heat. It is used mainly for duplication of master microfilm. It is less expensive than silver halide film, but is nor considered archival.

Water tear / torn

Pulling paper apart along a moistened line to produce soft, feathered edges. Used in paper/paste repairs.