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CARR McLEAN - Glossary Of Archival Terms
Glossary Of Archival Terms  
Acid is a substance capable of forming hydrogen ions when dissolved in
water. It can weaken cellulose in paper, board, and cloth, leading to
discolouration and embrittlement. Acids may also be introduced by migration
from other materials or from atmospheric pollution. See also pH and ACID

Acid-free materials have a pH of 7.0 or higher. Such materials may be
produced from any cellulose fiber source including cotton and wood, if
measures are taken during manufacture to eliminate active acid from the

The transfer of acid from an acidic material to a less acidic or pH neutral
material. This may occur directly, when two materials are in close contact.

Alkaline substances have a pH over 7.0. They may be added to material to
neutralize acids or as an alkaline reserve or buffer for the purpose of
counteracting acids that may form in the future. A number of chemicals may
be used as buffers; the most common are magnesium carbonate and calcium

American National Standards Institute. Sets national materials standards.
ANSI establishes criteria for storage enclosures and a wide variety of media
including paper, microfilm, etc.

Archival is a non-technical term that suggests a material or product is
permanent, durable, or chemically stable and is therefore suitable for
preservation purposes. Archivally safe materials are for the most part
inert and non-reactive. For example, plastic envelopes usually have
heat-sealed seams which eliminate problems associated with off gassing from
adhesives. Archival quality products are available in a wide array of
formats and materials including polyester, polyethylene and polypropylene.

An alkaline chemical used as a buffering agent in papers and boards.
Neutralizes acidic material.


It is the main component of many fibrous plant products, including paper and
some cloth.

The treatment of archival materials, artwork, or museum objects to stabilize
them or strengthen them physically, ensuring their survival as long as
possible in their original form. See also PRESERVATION.

A conservation treatment that neutralizes acids in materials such as paper.

In the encapsulation process, an item is enclosed between two sheets of
polyester film and sealed on all four sides with either double-sided tape or
a special polyester-welding machine. Encapsulation is useful for protecting
fragile documents, especially if they are torn. Polyester film is optically
clear and allows for easy viewing of the artifact.

Embedded in the cellular structure of plants, Lignin contributes to their
strength and rigidity and is found naturally, along with cellulose. It is
thought that Lignin contributes to chemical degradation. To a large extent,
it can be removed during manufacture.

The International standard SI (système internationale) for measuring visible
light such as sunlight and incandescent lighting. A unit of illumination
equal to one lumen per square meter, uniformly one meter distant from a
point source of one candela. One lux is equivalent to .0929 footcandle. The
only difference between lux and lumen is that lux takes into account the
area over which the luminous flux is spread.

A mil is a unit of thickness equaling one thousandth of an inch (.001").


Having a pH of 7, neither acid nor alkaline.

Ability of a material to resist chemical deterioration. Permanent paper
usually refers to a durable alkaline paper that is manufactured according to
ANSI Standards. See ANSI.

pH is a measure of the concentration of hydrogen ions in a solution, which
is a measure of acidity or alkalinity. Seven is pH neutral; numbers below 7
indicate increasing acidity with 1 being most acid. Numbers above 7 are an
indication of 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 8.5.

The test reveals whether storage enclosures such as boxes, envelopes, file
folders or canisters will damage photographs, negatives, slides, and motion
picture films. It can be used to assess potential photographic activity
caused by components including adhesives, inks, paints, labels, and tape.


An odourless, nontoxic, transparent, water-insoluble thermoplastic resin
used in emulsion paints and adhesives for sealing porous surfaces. Also
called PVA.

A plastic, often abbreviated as PVC. It is not as chemically stable as
other plastics, and emits hydrochloric acid as it deteriorates. Therefore,
it has no application in the preservation of books and paper.


Preservation is considered a broader term than Conservation. It includes
activities associated with maintaining library, archival, or museum
materials for use, either in their original physical form or in some other
format. The goal of preservation management is to slow down or minimize
physical change caused by use or storage over time.

The amount of water vapour in the air, expressed as a percentage of the
maximum amount required to saturate it at the same temperature. Ratio of
actual water vapour pressure to saturation vapour pressure.

Respect the guiding principle of conservation. Do not do anything that you
cannot undo. Conservators are the ones most qualified to repair valuable
artifacts. They have the expertise and knowledge to assess the condition of
an artifact and recommend a suitable course of action. For example, paper
conservators abide by the mender¹s rule; they do not use materials that are
either weaker or stronger than the items being mended.

Material used to screen out ultraviolet (UV) rays from visible light.
Ultraviolet radiation is potentially damaging to library, archival, and
museum collections and is present more in sunlight and fluorescent light
than in incandescent light. Removing UV radiation from storage and
exhibition spaces reduces the rate of deterioration and prolongs the life of
materials found there. Certain acrylic sheet materials have UV filtering
properties as well.

Van¹t Hoff¹s Rule states that chemical reactions double with every increase
of 10° C in temperature.