|
GLOSSARY
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | R | S | T | U | V | W
P
paper
A man-made substance, generally 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 composed of fibres from cotton or linen rags.
Modern papers are mostly made from wood pulp. The treatment given to the wood pulp affects the properties of the paper. Paper produced from an alkaline process are usually more stable than those produced from an acidic one. Acidic paper containing a high concentration of groundwood-for example, newspapers and hence a high lignin content-are very unstable.
Many Japanese papers are made by traditional methods from a variety of plant fibres. These are valued for their flexibility, strength and permanence.
paper fillers
See Filler.
paper-based material
Books, documents, art works, photographs and other objects produced on paper.
papermakers' alum
Aluminium sulphate, widely used in the papermaking industry to improve the flow of pulp through papermaking machines, and to fix rosin size to paper. See also Alumrosin sizing.
papyrus
A writing material made from the pith of a giant sedge found in the region of the Nile and used by the ancient Egyptians, Greeks and Romans. It was made by placing strips of pith-the nearer the centre the higher the quality-in a row and then overlaying them with another row placed at right angles to the first. These were moistened and beaten or pressed: a process which released natural gum and provided adhesion. The earliest recorded specimen was found in a tomb of around 3000 B.C.
parchment and vellum
Parchment and vellum are untanned animal skins. The skins are stretched and treated with lime, and scraped to remove fats and hair from the skins. They are dried and stretched. Because of the processing with lime, vellum and parchment are not particularly susceptible to acid deterioration.
Vellum and parchment are very moisture-sensitive. In high humidity conditions, the skins absorb moisture and can distort and cockle. As they dry in low-humidity conditions they become less flexible and distortions and creases can become set into the skin. Correct storage is important.
particulate matter
Solid particles suspended in the air. These solid particles may settle on surfaces depending on whether rain and wind is present. If the particles form the nucleus for the condensation of liquids, they are called aerosols. If particles settle on surfaces in still air, they are referred to as dust or grit.
passivating layers
Protective layers which form on particular metals; caused by oxide films which coat the surface and act as 'insulating' barriers to slow the rate of corrosion to acceptable levels. This type of passivation occurs with copper and aluminium.
paste papers
Papers on which the decorative designs have been made with paste to which colouring matter has been added.
pasteboard
In popular use, a term often applied to any stiff board or cardboard of medium thickness. It originally meant boards formed by laminating or pasting together a number of sheets of waste paper. In bookbinding, it is usually encased in a fabric or leather to make the cover of a book.
patina
The effect of the environment or artificial chemical and/or physical systems affecting the surface appearance of a work of art. For metals, this usually takes the form of a film of corrosion on the object, usually as a result of exposure to the elements. Many patinas are prized for their aesthetic value-for example on bronzes-or protective properties-for example on lead, tin or pewter.
perfect binding
A technique developed in the late 19th century for binding books without stitching or sewing their sections. It consisted of single leaves held together by means of a rubber solution applied to their back edges. This type of binding was a predecessor to the modern adhesive bindings now widely used for paperback books. Other types of adhesive are now used: mostly various kinds of PVA.
permanence
The stability of a material and its ability to resist chemical deterioration. It is not a quantifiable term.
permanent display
Continuous display of objects for an extended period. This is often made a condition of bequests, irrespective of the conservation needs of the objects, which might require periodic resting, that is, rotating from display to storage.
Perspex
An optically clear, thermoplastic resin, polymethyl methacrylate, used as a substitute for glass in certain applications-such as some picture frames. Perspex is a brand name; a similar product has the brand name Plexiglas.
pesticide
A general term for any material designed to kill pests. Pesticides include specific substances for killing insects-insecticides; fungi-fungicides; plants-herbicides; rats and mice-rodenticides; and other pests. There are two general categories of pesticides: biological pesticides which use growth regulators and pheromone attractants; and general pesticides which tend to use chemicals. See also Fungicide; Pheromone attractants.
pH
A scale of measurement ranging from 0-14 for identifying the level of acidity of solutions-the hydrogen ion H+ concentration. Pure water has a pH of 7 which is considered neutral, whereas acidic solutions fall below 7 and alkaline solutions have pH values exceeding 7.
phase box
A four-flap box originally invented to meet the immediate, short-term protection needs of an item within a phased conservation program-hence the name-established by the Library of Congress. This type of box is easy to make and is used widely to protect fragile volumes.
phased preservation
Collection maintenance activities such as the provision of simple boxes, folders or protective enclosures, rehousing and other preventative preservation procedures, while establishing priorities for future treatment.
pheromone attractants
Pheromones are chemical substances produced by insects to communicate messages. The pheromones that serve as food or sex signals are used as lures in insect traps.
photochemical, photochemistry
The effect on chemical reactions and the rate at which they proceed in the presence of electromagnetic radiation. Photochemistry is the branch of physical chemistry which studies the effects of light on chemical reactions.
photochemical deterioration
Deterioration reactions initiated by visible and ultraviolet light and sometimes infrared. Photochemical deterioration is a major cause of deterioration for paper-based material and textiles.
photochemical reactions
Chemical reactions initiated, assisted or accelerated by exposure to light. For example, hydrogen and chlorine combine explosively on exposure to sunlight, but only slowly in the dark.
photographic quality
Of such a quality that processing, materials and techniques will actively protect photographic prints from damage and will ensure the maximum life span for the photographic prints.
photographic-quality mountboard
Mount/mat board manufactured without additives or elements damaging to photographs, that is, boards which are acid- and sulphur-free. See also Mounts, mats.
physical damage
Damage to objects including that caused by mechanical rather than chemical means and resulting in cracks, chips, splits, tears, dents, punctures, breaks, scratches, scuffs and abrasions, as well as soiling, wear and tear, warping, shrinkage, separation of layers of composite materials, graffiti and insect attack.
pigment
Dry coloured substance in granular state which is mixed, usually ground, with a liquid binding agent such as drying oil, egg white or gum to form a paint.
Pigments usually give body as well as colour to the paint-unlike dyes, which do not add body. The principal characteristic of a pigment which distinguishes it from a dye is that it is insoluble in the medium in which it is used, whereas a dye is completely dissolved in its medium. There are numerous instances in which the same chemical product serves as either a dye or a pigment. See also Dye.
Plastazote, Evazote
Polyethylene foams made of relatively inert materials which will not deteriorate or give off harmful gases, used for padding storage boxes and rolls-this is a trademark/brand name.
plastic memory
The tendency of a material which has been stretched or warped to return to that shape, even after corrective measures have been taken.
plasticiser
A chemical added to another material to give it increased flexibility. In some plastics such as PVC, plasticisers leach out in time leaving the material brittle. Adhesives for use in preservation should be internally plasticised.
Plexiglas
See Perspex.
plinth
A low, raised base usually square and rising only a few inches from the ground, which surrounds a display stand. Plinths are used to form a protective barrier so that visitors cannot get too close to an object on display.
pollutants
Gases and airborne particulate matter usually resulting from combustion or venting of chemicals associated with human, industrial or other activities. Pollutants are one of the major causes of deterioration of museum objects.
polyester
The term polyester refers to a class of plastics, only some of which are suitable for use in conservation. In a conservation context it usually refers to a clear, plastic sheet made from polyethylene terephthalate. It is noted for its crease resistance, strength, durability and resistance to moisture and chemicals. Mylar and Dacron are polyester products used widely in conservation work. See also Myalr, Mylar D; Dacron.
polyethylene
A chemically inert, stable, highly flexible, transparent or translucent thermoplastic material. It is fungi-resistant and used in preservation as a protective liner, enclosure, or stable plastic bag. Tyvek is a polyethylene product.
polymer
A large organic compound made up of a series of smaller repeating units-monomers-joined together by chemical bonds in a regular pattern. The molecular size of the polymer helps to determine the mechanical properties of the plastic material and ranges from a few hundred of the basic units to hundreds of thousands.
polypropylene
A plastic polymer of propylene, similar to polythene but stronger; as a plastic sheet it is softer than polyesters such as Mylar. In a conservation context, it is used commonly to make sleeves for slides, linings for photographic storage boxes, protective transparent covers for book dust jackets, and Copysafe storage sleeves. See also Polyester; Mylar, Mylar D.
preservation
All actions taken to slow deterioration of, or prevent damage to, cultural material. Preservation involves controlling the environment and conditions of use, and may include treatment in order to, as nearly as possible, maintain an object in an unchanging state. In the case of archival material, moving image and sound, this may include transfer to another medium. See also Conservation; Restoration.
Preservation is a broader term than conservation: conservation activities form part of a total preservation program. Preservation includes activities carried out to repair or treat damaged materials and activities taken to prevent or delay material becoming damaged-preventative preservation.
pressure sensitive tape
Sometimes called 'sticky tape'. Adhesive tape that adheres to a surface when pressure is applied. The adhesive frequently degrades leaving a brown residue, which stains and makes the paper brittle. Some conservation grade pressure sensitive tapes are available but they are not recommended for use on original materials.
preventive conservation
All actions undertaken to prevent the deterioration of cultural materials and collections. See also Preservation.
printing-out paper
Light-sensitive photographic paper which was printed in direct contact with a negative and exposed to sunlight. There was no chemical development involved in the production of printed-out images. See also Developing-out paper.
Protecta Foam
See Cellair.
provenance
The proven or documented place of origin, use, history and ownership of an object.
psychrometer/sling psychrometer
An instrument used to measure temperature and relative humidity. Sling psychrometers are relatively inexpensive compared to thermohydrographs. They provide accurate instant readings but do not permit the recording of temperature and relative humidity over time.
pulp
The mechanically and/or chemically prepared fibrous mixture used in the manufacture of paper and board. Mechanical pulping separates the wood fibres, while chemical pulping purifies them by removing lignin and other undesirable agents.
PVA, polyvinyl acetate
A thermoplastic with good ageing characteristics, sometimes used as a fixative or sealing agent. PVA is a polymer emulsion and forms a generally insoluble film much like emulsion paints. When applied to a surface, PVA is liquid, but as it dries it forms a continuous solid film. The use of this substance in book repairs is limited because it is not readily reversible. See also Acid-free PVA.
PVC, polyvinyl chloride
A polymer of vinyl chloride. This plastic is not chemically stable and produces hydrochloric acid as it deteriorates. It should not be used for conservation purposes.
Plasticisers are used to make PVC more flexible. These leach out over time and cause significant damage. See also Chlorinated hydrocarbons.
|
