Library Preservation Glossary

The glossary that follows contains some of the most common technical words used in the literature of library preservation, and the way they are used in this program. Wherever possible, an attempt has been made to describe these words in non-technical, more easily understood terms. You are likely to encounter alternative definitions of some of these terms in the conservation literature as definitions change and are interpreted differently in different areas of conservation. You will also find that some terms are used differently from country to country, and even in different regions in the same country.

The glossary that follows 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 p14-15

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

Acid (adj. acidic)
In chemistry, a substance capable of forming hydrogen (H+) ions when dissolved in water. Acids can damage cellulose in paper, board and cloth, by weakening or breaking their molecular bonds leading to embrittlement. Acids may be introduced during the manufacture of library materials, or may be present in the raw material. Acids may also be introduced by migration or from atmospheric pollution. They can be neutralised by an alkali to form a salt
Acid deterioration
The weakening of paper structure by an acid through hydrolysis or other means, resulting in a breaking down of the chain length of the material , and a subsequent loss of strength. This can become so severe that the paper has almost no residual strength and is 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. Sincecellulose is damaged by acids, acid free materials are desirable in library 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 staining.
Acrylic
A plastic material noted for its transparency, weather resistance, colour fastness and transparency. 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 the sheet form 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.
Adhesive
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. Pressure sensitive or 'sticky' tapes should not be used for materials intended for long term preservation, since the adhesive degrades and yellows and the adhesive residues can become impossible to remove.
Alkali (adj: alkaline)
In chemistry, a substance capable of forming hydroxyl (OH-) ions when dissolved in water. Alkaline materials may be added to materials to neutralise acids or as 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 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. Leaves an acidic reserve in the paper. Alum/rosin sizes were used extensively in the past, and have contributed significantly to the brittle book problem.
Ambient conditions
The existing conditions of temperature and humidity in any building or room.
Archival quality
An imprecise 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 exists that describe how long an 'archival' material will last. The word permanent is sometimes used to mean the same thing.
Backing
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.
Bleaching
The cosmetic whitening or reduction of coloured substances 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 preservation.
Bleeding
The loss or spreading of colour when coloured paper or ink comes in contact with water or other solutions.
Blocking
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. 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
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 smooth, flat tool made of animal bone or plastic 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 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 not dry flat unless subjected to some force or pressure.
Buffer/buffering
A process sometimes used in conjunction with deacidificationor 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.
Cellulose
Chemically, a complex carbohydrate. 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. The traditional Western plants providing cellulose for paper were cotton and linen ('rag' paper). Wood is the major source of papermaking fibres today.
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 pigment etc) in order to improve its finish in terms of printability, smoothness, opacity. Coated papers usually have a glossy appearance and are sometimes called 'art papers. Clay coated papers have a tendency to block when they are exposed to high relative humidity or become wet.
Conservator
A person professionally responsible for the physical preservation of collection items or their informational content.
Conservation
The use of procedures to preserve and repair the physical structure of an item. All processes ideally should be reversible.
Deacidification
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.
Deterioration
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 filming 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 should 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.
Durability
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.
Encapsulation
A 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 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.
Environmental control
The maintenance of safe levels of light exposure, humidity, temperature, air pollution, air movement, dirt inside a building.
Facsimile
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.
Foxing
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 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.
Fumigation
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.
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 materials. Keeping the relative humidity below 70-80% and providing good air movement is the best way to control the growth of mould.
Fungicide
A substance capable of destroying or preventing the growth of fungi. Fungicides do not provide any residual protection from future mould growth.
Glue
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.
Grain
In machine made paper and board, the direction in which the fibres predominantly lie. Grain direction needs careful consideration in bookbinding and paper conservation treatments.
Groundwood paper
See: Paper
Head
The top of a book as it sits upright
Hot melt adhesive
An adhesive which is liquid when hot but solid at room temperature. Hot melt adhesives are extensively used in paperback bindings, but are generally inflexible and can become brittle and yellow. Pages become easily detached when this happens.
Humidity
The moisture in the air. See also: Relative humidity
Hydrolysis
A chemical action involving water - decomposition in which a compound is split into other compounds by taking up water.
Hygrometer
See: Psychrometer
Hygrothermograph
See: Thermohygrograph
Inlaying
A technique used to repair and strengthen documents, whereby they are adhered into a frame of paper whose dimensions are slightly smaller than the document itself.
Inert
See: Chemical stability
Interleaving
A process of using sheets of paper or other material to separate items. Buffering paper is often recommended to be put between acid materials to prevent acid migration
Insecticide
A pesticide used to kill insect life.
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 recorded information contained in it.
Lamination
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.
Lignin
A component of the cell walls of plants, 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. There can be large amounts of lignin present in pulp made form wood. It is not removed in the production of mechanical pulp, but using chemical processes, it can be optimally removed.
Medium/media
The material on which information is recorded. Sometimes also refers to the actual material used to record the image.
Microfiche
A sheet of flat photographic film, usually 4 x 6 inches in size, containing rows of images with an eye legible title.
Microfilm
Photographic film used in micrographics, usually in roll form 35mm or 16mm wide. 35mm format is preferred for preservation microfilming.
Microform
A term to describe both microfilm and microfiche formats.
Micrographics
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
Mylar
See: Polyester
Neutral (adj: neutralise)
In chemical terms, having a pH of 7; neither acid nor alkaline.
Oxidation
A chemical process where a compound combines with oxygen to form a different compound.
Pamphlet
A book composed of less than 100 pages (typically) and usually given only a paper cover.
Paper
In general, matted or felted sheets 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. Japanese paper is made by traditional methods from a variety of plant fibres - valued for its properties of flexibility, strength and permanence.
 
Paste
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 may be added to give an adhesive combining its fast drying and strength with the working qualities of paste where long term reversibility is not required.
Permanence
The stability of a material and its ability to resist chemical deterioration - not a quantifiable term.
Permanent
See: Archival. A permanent paper is one which conforms to an agreed standard, is usually acidfree and made to resist changes to a greater degree than is usual in other papers.
pH
In chemistry, pH is a measure of the concentration of hydrogen ions in solution, which is a measure of acidity or alkalinity. 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.
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.
Phase box
A simple, economical box designed to provide a good degree of protection to its contents without undertaking full conservation treatment. Initially developed to provide intermediate protection to materials awaiting further treatment.
Photochemical degradation
Damage caused or increased by exposure to light.
Plasticiser
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'.
Point
A unit of measuring the thickness of paper. One point equals 1/1000th on an inch.
Polyester
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, and book jackets. Trade names include Mylar and Melinex. Used in web form ('Reemay')to support paper during wet treatments, and as a relatively nonstick surface through which moisture can pass during mending, drying etc.
Polyethylene
In its pure form, a chemically stable plastic material. Used in film form to make sleeves for photographic materials and other uses. A cheaper alternative to polyester film.
Polymer
In chemistry, a large organic compound made up of a series of smaller repeating units joined together by chemical bonds in a regular
Polypropylene
In its pure form, a chemically stable plastic material. Used in film form to make sleeves for photographic materials and other uses. Used in sheet form for boxes, folders and such. A cheaper alternative to polyester film.
Polyvinylacetate
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 or 'white glue'. They have a milk like appearance, but dry clear.
Polyvinylchloride
Plastic usually abbreviated as PVC, or sometimes 'vinyl'. Not as chemically stable as some other plastics. It can emit acidic components which damage cellulosic materials. Added chemicals called plasticisers are also used to make PVC more flexible. These also damage library materials.
Preservation
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 adhesivetape that attaches to a surface when pressure is applied. The adhesive frequently degrades leaving a brown residue which stains and embrittles paper. Not recommended for materials intended for long term preservation.
Psychrometer/sling psychrometer
A simple instrument used to measure temperature and relative humiditySling psychrometer's are relatively inexpensive to purchase compared to a thermohygrograph, but are very accurate when used properly.
Pulp
Raw material from which paper is made. Fibrous materials, generally from plant materials including trees, made ready for use in the manufacture of paper or board. Mechanically or chemically prepared mixtures obtained from wood or vegetable fibres to be used in the manufacture of paper and board. Groundwood pulp, which is produced by mechanical methods contains lignin and has poor durability. Chemical pulp has a considerable amount of non cellulosic material removed during processing, and paper made from it has, as a result has a higher durability than groundwood paper. Permanent papers and boards can be made from chemical pulp.
PVA
See: Polyvinylacetate
PVC
See: Polyvinylchloride
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.
Reprography
A range of processes used to copy or produce reproductions of items by optical or photographic means - including photography, photocopying, and microfilming.
Reproduction
See: Facsimile. A copy of an original item, not necessarily in the same form.

Reversibility

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 which 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 permanentpapers are alkaline.
Slipcase
A well fitting open ended case into which a book may be slipped or pushed for protection, leaving the spine displayed.
Spine
The back edge of a book; opposite to the fore-edge.
Surrogate
A copy of the information content of an original item in another medium, usually one which is more durable. See also: Reproduction and Facsimile.
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.
Thermohygrograph
A machine which records temperature and relative humidity. 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 dataloggers are preferable.
Ultraviolet light (UV)
Light having a shorter wavelength and higher energy than visible light. Ultraviolet light is potentially damaging to library, archive and museum objects. Removing UV light can reduce the rate of deterioration. Certain acrylicsheets 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 not considered archival.
Water tear/torn
Pulling paper apart along a moistened line to produce soft, feathered edges. Used in paper/paste repairs.