Glossary of Terms
"In principle, papers which contain no free acid and have
a pH value of 7.0 or greater. In practice, papermakers consider
a paper having a pH value of 6.0 or greater to be acid free.
Such papers may be produced from cotton fibers, rags, esparto,
jute, chemical wood pulps, or virtually any other fiber, with
special precautions being taken during manufacture to eliminate
any active acid that might be present in the paper pulp. However
free of acid the paper may be immediately after manufacture,
the presence of residual chlorine from bleaching operations,
aluminum sulfate (alum) from sizing, or sulfur dioxide in the
atmosphere, may lead to the formation of hydrochloric or sulfuric
acid unless the paper has been buffered with a substance capable
of neutralizing acids."
Electronic edition of Roberts, Matt,
and Etherington, Don, Bookbinding and the conservation of
books: a dictionary of descriptive terminology. 1982, Library
of Congress, Z266.7.R62 686.3'03 810607974 ISBN O-84440-0366-O
AACR2, prepared by Walter Henry, Preservation Department, Stanford
University Libraries, Spring, 1994.
A substance is labeled "acidic" when it measures lower
than a 7 on the pH scale. The lower the number the more "acidic"
the substance is. The pH scale is logarithmic which means that
each unit along the scale is logarithmically not linearly, larger
or smaller than the number next to it. So, changes in pH from
one number to the next are very significant.
Also known as a "base", an alkaline substance measures
higher than a 7 on the pH scale. The higher the number the more
"alkaline" the substance is. The pH scale is logarithmic
which means that each unit along the scale is logarithmically
not linearly, larger or smaller than the number next to it. So,
changes in pH from one number to the next are very significant.
An early photograph in which the image is made by underexposing
an image onto a wet collodion coated glass plate. The image was
made to appear positive by placing it over a dark background.
This term is used loosely to describe a material that has been
made for long- term stability. There is no official definition
of the term, and it can be used to mean anything from "neutral
at the time of manufacture" to "acid-free, lignin-free,
sulfur-free, optical brightener-free".
Bone china: Bone china was developed in England in the
18th century to imitate and compete with Chinese porcelain. It
combines animal bone ash with hard paste porcelain and fired
Materials can be buffered by incorporating an alkaline additive,
like calcium carbonate, into their structure during manufacture.
The alkaline additive, sometimes called an alkaline reserve,
is designed to neutralize any acids that are formed by the base
material during aging. . Buffered products should not be used
around protein-based materials like silk, wool, some photographs,
leather, parchment, or vellum.
An inert solid material formed when slaked lime (calcium hydroxide)
combines with carbon dioxide in the air. Calcium carbonate is
used in conservation to polish silver. It is also used as a buffering
Cellulose is the main complex carbohydrate polymer found in plant
fibers. It is used in the manufacture of fibrous products such
as paper, textiles, and explosives.
Composition or "compo" is used to decorate wooden frames.
Compo can be made of a variety of mixtures such as wood pulp
and adhesive; calcium carbonate and adhesive; plaster; or paper
pulp and adhesive. It is usually cast or pressed into molds to
form elaborate elements and then glued to the wood frame where
it is varnished, painted or gilded.
A conservator is an individual who, through formal training and
practical experience cares for historic and artistic works. They
provide direction and advice on the preventive care of collections
including display, environmental control, storage, handling,
packing, and shipping. Conservators also are specialists in the
treatment of objects and the identification of materials and
techniques that are used to make objects and works of art. See
Conservation is the profession dedicated to the preservation
of historic and artistic objects. Conservation aims to preserve
all aspects of the object's original materials through documentation,
treatment, and preventive care and through research and education.
Conservation Assessment: The Conservation Assessment is a tool designed
to help institutions learn about their current ability to preserve
their collections. Practices are measured against current professional
best practice standards. The Conservation Assessment provides
a report on the policies, practices, and conditions within an
institution and focuses on the following areas: general institution
overview, staffing, building and facilities, environmental control,
collection and collection policies, exhibition, storage, security
and safety, and emergency preparedness. The IMLS Conservation
Assessment Technical Assistance Program, managed by Heritage
Preservation, Inc. offers this technical assistance on a first
come first served basis. Visit their website at http://www.heritagepreservation.org/CAP/index.html.
Crazing: Minute cracks in the surface of glaze, glass,
or painted surfaces.
Fine surface cracks in ceramic glazes (similar to crazing) and
An early type of photograph in which the image is exposed directly
onto a copper plate coated with a highly polished silver surface.
The copper plate is made sensitive to light using iodine fumes
and is exposed in a camera. Unlike later photographic processes,
the daguerreotype is a direct positive-image process with no
Electronic or battery-powered instruments that record environmental
conditions such as temperature, relative humidity, and light
levels over periods of time. Data loggers are connected to a
computer terminal and proprietary software is used to download
the recorded data and produce needed reports.
Water that has been treated to remove ions, microorganisms, and
most other impurities.
Water that has been treated to remove all impurities such as
solid materials, inorganic, and organic materials.
Earthenware is a porous ceramic body that is made of a mixture
of materials including potash, feldspar, sand, and clay. It is
very porous due to its low biscuit firing (first fire) at temperature
around 1000ºC. Due to its high porosity, earthenware is
water permeable must be glazed to keep it watertight. Common
forms of earthenware include slipware, creamware, terracotta,
Feldspar is the name of a group of rock-forming crystals. It
is usually used as an ingredient for earthenware and other ceramic
bodies often with sand and clay.
A ferule is the metal or plastic casing on a brush between the
handle and the brush hairs. It holds the bristle portion to the
In framing, a fillet is a thin, inner frame placed between the
paper and the glass to prevent contact between the two.
Easily breakable; crumbles; reduced to powder; occurs with organic
and inorganic substances (paper, leather, glass, textiles, ceramics,
A foot-candle is a non-metric unit of measurement used to describe
light intensity. It is defined as the amount of light received
by 1 square foot of surface placed a distance of 1 foot from
the light source.
Small, irregular yellow-brown spots/stains found on paper objects
and works of art on paper. Conservators believe these marks are
caused by mold or metal impurities in the paper.
Fugitive colors: Dyes and colorants that are unstable
and easily dissolved by water or faded by light or other atmospheric
a thin transparent or semitransparent paper often times used
in wrapping, packing, and interleaving photographs, illustrations,
books, and fine works of art. Acid-free glassine paper is commonly
used in the storage of photographs and negative films. The use
of acid-free glassine paper is highly discouraged in the storage
of photographs for it may become embedded in the photographic
emulsions on the photographs, especially in humid conditions.
A coating of gold applied to a substrate through a variety of
methods including electrolytic deposition, application of leaf,
application of paint, and burnishing.
High Efficiency Particulate Air filter. The filters are designed
to remove 99.97% of all air pollutants that measure 0.3 micron
or larger at a specified flow rate of air. A HEPA filter is essential
for use in the cleaning of mold, asbestos, pesticide, lead, insect
eggs, soot, or any other contaminants from heirlooms and museum
Heritage Health Index: The Heritage Health Index is the first comprehensive
survey ever conducted of the condition and preservation needs
of our nation's collections. The projects was conceived and implemented
by the non profit organization Heritage Preservation, Inc. in
partnership with the federal Institute for Museum and Library
Services and other funders. To learn more about the survey and
its findings visit http://www.heritagepreservation.org/HHI/index.html.
An instrument that is a used to measure relative humidity in
the air. It contains a moisture absorbing and releasing element
that dimensionally changes according to humidity changes. The
dimension changes can be recorded.
An instrument that is used to measure relative humidity in the
air. It records temperature and relative humidity levels on a
chart for a set period of time (one day, one week, one month,
or two months).
An inert substance does not readily react; is chemically stable.
To replace missing areas of an object with similar material for
support. The related noun in "fill" which described
the material used to fill in a loss.
Infrared is a form of electromagnetic radiation. It is adjacent
to the visible light spectrum, just beyond the longer wavelength
red region. The energy of infrared radiation can break the chemical
bonds in materials leading to the degradation of artifacts and
works of art. It is detected by humans as heat.
To add colored or textured media to fills, repairs, or areas
of loss in order to create a sense of continuity in a work of
art or artifact.
Japanese Haké brushes: A wide brush used in Japan
to apply damp sheets of paper on to a drying surface. The bristles
are made of horse or other animal hair or plant fibers and are
very absorbent and soft.
A component of the cell walls of plants. It is unstable, light
sensitive, and as it ages, breaks down into acid components.
It contributes to the degradation of paper products, and it can
be largely removed during the paper making process.
lux is the international standard unit of measurement to describe
light exposure. It is defined as the amount of visible light
per square meter illuminated on a surface. One lux = 0.093 foot-candles.
Marvelseal® is a material made of layers of aluminized polyethylene
and polypropylene film. It is resistant to the transmission of
water, water vapor, and other atmospheric gasses making it suitable
for humidity controlled shipping or in the fabrication of storage
bags. Marvelseal® is ideal for lining shipping crates, exhibit
cases, and shelving to reduce the amount of off-gassing from
exposed wood surfaces. It is available from most conservation
A microclimate is a smaller, self-contained environment within
a larger environment. A microclimate can constitute an advantageous
change from the ambient environment (buffered RH changes) or
a detrimental change (condensation in an enclosed space).
Microcrystalline paste wax: A paste wax made with microcrystalline waxes
of differing melting points, a solvent (usually Mineral Spirits),
and other additives. Paste wax recipes are customized for the
intended use. For example a paste wax recipe for an outdoor sculpture
in Alaska will have a different formulation than a paste wax
recipe for use in Las Vegas.
Microcrystalline wax: Microcrystalline wax is a refined, paraffinic
wax that is crystalline in structure. It is colorless, odorless,
and translucent and is a by product of the petroleum refinement
Trademark name for inert sheets of clear polyester. Mylar is
often used in the storage of fragile objects such as paper or
photographs. It is available from most conservation and archival
suppliers. Conservation grade polyester materials include Mylar
D by DuPont and Melinex 516 by ICI.
Scientists consider a solution to be neutral when its pH level
is 7. This means the solution is neither alkaline nor acidic.
Nitrate Film: Film
made from nitrated cellulose polymers. Highly nitrated film base,
used for movie film and early photographic negatives, can be
chemically unstable and has been known to spontaneously ignite
Nitrile gloves are synthetic gloves that have low resistance
to friction, are easy to slide on, have a higher degree of flexibility,
and solvent resistance.
Emitting volatile chemicals, often acids and pollutants.
The change in appearance of an object's surface that may be seen
as a different color, saturation, or texture. On metals, it is
a form of corrosion or oxidation. On organic materials, it is
often caused by oxidation and by use wear, where skin oils and
other materials are deposited on the surface. Patina can be natural
or artificial; desired or disfiguring.
Allows water (or gasses) to pass through.
is the measure of hydrogen ion activity in a solution. The scale
ranges from 0 to 14. Each number increment specifies a ten fold
increase in hydrogen ion activity. Acidic solutions range from
0 to 7, with 1 being the most acid. A pH of 7 is neutral. Alkaline
solutions range from 8 to 14, with a maximum alkalinity of 14.
The pH can be measured, always in water, with pH strips or with
a pH meter.
Photographic Activity Test (PAT): PAT is an internationally recognized standardized
test for the safety photographic storage materials (ISO Standard
The yarn or supplementary threads (in velvet and/or rugs, for
example) that stand up from the plain of the weave.
An inert plastic that is recognized as being safe for storage
of artifacts. It is frequently used in making plastic sleeves,
folders, and encapsulations. Conservation grade polyester materials
include Mylar D by DuPont and Melinex 516 by ICI.
An inert plastic that is recognized as being safe for the storage
A chemically stable plastic recognized as being safe for the
storage of artifacts.
Polyvinyl Chloride (PVC): PVC is a chemically unstable plastic and
is not recommended for the storage of objects. PVC degrades as
it ages and emits compounds that form hydrochloric acid that
can be very damaging to paper-based collections.
Porcelain is a hard, translucent ceramic body that is vitreous
or semi-vitreous and is made with feldspathic minerals. Hard-paste
porcelain is fired around 1450ºC while soft-paste porcelain
is fired around 1200ºC. It is a hard, non-porous, waterproof
ceramic body. Porcelain fused intimately with applied glazes.
Material that contains many small, interconnected holes (pores)
that allow water, air, or other materials to pass through them
Potash: Potash is potassium carbonate often derived from
wood ashes. It is used in the manufacture of glass, soap, and
as a fertilizer.
Preventive Conservation: Preventive conservation is an applied form of
conservation that seeks to delay the natural or accidental degradation
of cultural objects through proactive measures that address safe
conditions for management, storage, use, transportation, or exhibition
Pre-washed fabrics have been washed prior to purchase. To pre-wash
fabric at home, wash the fabric in a clothes washer with a gentle
detergent, such as Ivory Snow©. Do not use bleach, fabric
softener, or any other laundry additive. Use the extra rinse
cycle, if it is available. Dry the fabric with no fabric softener.
A psychrometer is an instrument used to measure the moisture
content of the air. It compares the readings between a wet-bulb
thermometer and a dry-bulb thermometer to determine the relative
humidity or used electronic means to do the same.
term used to describe paper or paper products made from fabric
linen or cotton fibers. Traditionally, before the 1840's, actual
discarded rags were cleaned and degraded and used to make paper
pulp. Rag pulp paper is of high quality and is acid free and
Relative Humidity (RH): The amount of water that the air can hold at
a specific temperature. It expresses the relationship between
moisture in the air to the maximum amount of moisture that could
be present in the air at a given temperature. RH is expressed
as a percentage.
Reversibility is an important tenet in conservation. It is the
ability to undo a treatment procedure without negatively altering
the work of art or artifact.
Safe fabrics include pre-washed white or unbleached 100% cotton,
100% linen, or a 100% cotton/linen blend. Some dyes are unstable
over time or can interact with certain materials such as silver.
Dyed fabrics should be avoided. Some polyester and nylon fabrics
can be safe if they are not dyed or coated with harmful chemicals
such as fire retardants and surface finishes. It is best to check
with a conservator before selecting polyester and nylon fabrics.
Safe solid foams:
Safe solid foams are generally made of safe polymers or are made
using inert materials so that they do not emit harmful chemicals
upon aging. They include polyethylene and polypropylene foams
that are made without aggressive catalysts. Some common brand
names are Ethafoam© (dow.com) and Volara© (voltek.com).
Safe plastics are plastics that do not emit harmful chemicals
upon ageing. They are safe for the storage of heirlooms. They
include acrylic polymers, polyethylene, polypropylene, Teflon©,
polycarbonate, polystyrene, and polyester (Mylar D©). They
can be made into solid sheets, film, or plastic bags. Generally,
food grade polyethylene and polypropylene bags and boxes are
safe. Look for the symbols 1: PETE (polyethylene terephthalate),
2: HDPE (high density polyethylene), 3: LDPE (low density polyethylene),
4: PP (polypropylene), and 5: PS (polystyrene) and in the recycling
triangle on the bottom of boxes and other containers.
A solvent is a liquid that is capable of dissolving or dispersing
a solid or other liquid. Conservation solvents are volatile solutions
such as acetone, Mineral spirits, alcohols, etc. that can be
used to remove a compound from an object surface or used to aid
in penetrating a thick or solid material. They have serious health
affects and should be used with great care following all safety
Stoneware is a type of ceramic body that is vitreous or semi-vitreous.
It is a hard, strong, impermeable ceramic body. Stoneware is
fired between 1200ºC and 1350ºC. It is often used for
industrial and exterior applications.
A text block is the stack of leaves or gatherings of paper that
are to be bound into a book. The text block does not include
the endpapers or boards that are added during binding.
A tintype is a positive image on a sheet of thin iron coated
with black lacquer The iron is coated with a wet collodion solution
and placed in the camera. The late was immediately processed
Ultraviolet (UV) is not visible to the naked eye. The wavelengths
are shorter and more powerful than those in the visible and infrared
regions. UV light rays are longer than X rays. UV rays can be
very damaging to works of art and artifacts.
Unbuffered material contains no alkaline chemical additives to
counteract the formation of acids. Unbuffered storage materials
are preferred for items with proteins such as wool, silk, and
"Wet" clean: To clean by immersion in water or with a water-based
Microcrystalline structures that can trap acid gasses, oxidizing
gases, and atmospheric pollutants. These are used in clumping
kitty litter and were developed for the shrimp farming industry
to absorb and hold the acids produced in tanks by shrimp.
Recommendations in this website/pdf/video
are provided as a public service for guidance only. Neither inclusion
nor exclusion of products or providers constitutes endorsement
or lack thereof. The Gerald R. Ford Conservation Center does
not assume responsibility or liability, expressed or implied,
for any resulting activities involving any collections or objects.