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 http://palimpsest.stanford.edu/lex/ 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: firstname.lastname@example.org
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
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.
The weakening of paper or board structure by an acid,
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.
In chemistry, materials that have a pH
of 7(neutral) or higher
). Acid free paper is often alkaline buffered
. Since cellulose
is damaged by acids, acid free materials are desirable in library and
The transfer of acid from an acidic material to a less
, 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
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
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
to provide an alkaline reserve or buffer
for the purpose of counteracting
may form in the future. While a number of chemicals may be used as alkaline
, 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
The existing conditions of temperature and humidity
in any building or room
A term suggesting that a material, product
or process is durable
chemically stable; that it has a long life; and can therefore can be
used for preservation
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
Blocking is less likely to be a problem with modern coated papers.
Soft, unsized paper
used to absorb moisture.
Blotting paper used in conservation should not be coloured.
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.
A very useful small smooth, flat tool made of animal bone
or plastic and used to remove air bubbles, smooth, flatten crease or
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
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
chemical used as a buffer
in paper and
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 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.
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.
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
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
to counteract future acid attack. While deacidification may increase
the chemical stability of paper, it does not restore strength or flexibility
Dehumidifier (adj: dehumidification)
Equipment that reduces the humidity
in the atmosphere by the use of refrigeration, desiccants or absorbent
Damage caused to an item by physical, chemical or biological
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
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
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
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.
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.
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
Discolouration on paper, generally in the form of random rust
coloured spots. Believed to be caused by one or more of the following; fungus
, impurities in manufacture, high humidity
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
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
made from protein derived from the collagen in animal
products such as hides and bones. Animal glues become yellow and brittle
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.
The top of a book as it sits upright
Hot melt 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.
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
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
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
. 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
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
. The use of
photographic processes to produce very small images of original materials.
Types of microformat include the above.
Mould / mold
Neutral (adj: neutralise)
In chemical terms, having a pH
of 7; neither
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
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
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
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
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.
. 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
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
used in libraries and archives typically have a pH above 7 and below
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.
Collections maintenance activities such as the provision
of simple boxes, folders or protective enclosures, rehousing and other
preventive preservation procedures, while establishing priorities for
Damage caused or increased by exposure to light.
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.
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.
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
In chemistry, a large organic compound made up of a series of
smaller repeating units joined together by chemical bonds in a regular
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
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.
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
Pressure sensitive tape
Sometimes called 'sticky' tape. An adhesive
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.
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
during processing, and the resultant paper has a higher durability than
groundwood paper. Permanent
papers and boards can be made from chemical
The process of converting information from one form to
another - see also reprography
. 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
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,
. 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
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
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
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
Automatic computer-based dataloggers are preferable, being cheaper and
more versatile than thermohygrographs.
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.
A material used to filter the ultraviolet rays out of visible
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.