ANSI - Abbreviation for the American National Standards Institute.

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Acid-free - In chemistry, materials that have a pH of 7.0 or higher. Sometimes used incorrectly as a synonym for alkaline or buffered. Such materials may be produced or buffered. They may be produced from virtually any cellulose fiber source (cotton and wood, among others), if proper measures are taken during manufacture. Active acid from bleaching, aluminum sulfate from sizing, or pollutants in the atmosphere may lead to the formation of acid unless the paper or board has been buffered with an alkaline substance.

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Archival - A non-technical term that suggests that a material or product is permanent, durable, or chemically-stable, and that it can therefore safely be used for preservation purposes. The phrase is not quantifiable: no standards exist that describe how long an "archival" or "archivally-sound" material will last.

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Beveled Edge - An edge tapered at an angle to make a more gradual transition between an upper and a lower surface. The beveled edge of a mat inclines about 60 degrees.

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Buffering - The addition of alkaline agents such as calcium or magnesium carbonate during the papermaking process in order to counteract the effect of acidic contamination. The degree of buffering (usually 2-3%) is measured by percentage of paper weight. See alkaline.

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Calcium Carbonate - An alkaline chemical used as a buffer in papers and boards.

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Chromogenic dyes - Dyes or color produced in a color print by a colorless dye pre-cursor embedded in the photographic emulsion combined with a dye coupler in the developer solution. The interaction of the two after the exposure to light produces a color print. Prints are produced from color negatives.

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CRI rating - Abbreviation for Color Rendering Index. Represents a numerical rating (95 being the standard) for overall brightness and evenness of a viewing light field, as in that of a light table.

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Deacidification - A common term for a chemical treatment that neutralizes acid in a material such as paper and deposits an alkaline buffer to counteract future acid attack. While deacidification increases the chemical stability of paper, it does not restore strength or flexibility to brittle materials. See also pH.

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Dessicant - Any agent--particularly a silica gel--that removes gaseous water from the air and reduces relative humidity. Desiccants can be used in sealed enclosures to protect photographs from humidity. Since silica gels can be made to give up their absorbed moisture by heating, desiccants may be reused.

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Emulsion - The light-sensitive coating on photographic film or printing paper.

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Encapsulation - A form of protective enclosure for papers and other flat objects which involves placing an item between two sheets of transparent polyester film that are subsequently sealed around all edges. The object is thus physically supported and protected from the atmosphere, although it may continue to deteriorate in the capsule. Because the object is not adhered to the polyester, it can be removed simply by cutting one or more edges of the polyester. Fiber-Base Paper - Printing paper whose base material is a high-quality paper.

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Lignin - An acid organic substance found in wood pulp. It is removed in the chemical pulping process, but it is not removed in the manufacture of low-grade papers made of ground wood pulp, such as newsprint.

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Melinex (polyester) - A Dupont trade name for a clear, flexible polyester plastic sheet that is often used to cover prints. Melinex has been extensively tested and is approved for photographic use.

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Nitrate-based film - Film base for emulsions popular in the 1920s and 1930s. Composed of cellulose nitrate, a somewhat dangerous compound known for its flammability and explosive properties. Requires special storage conditions including a buffered paper environment and/or cold storage.

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Non-buffered - As in non-buffered paper, pulp which is not impregnated with buffering agents such as calcium carbonate. Some buffering agents have adverse effects on various types of photographic prints.

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PAT (Photographic Activity Test) - Accelerated aging test using a specialized photo-emulsion in contact with a paper sample at elevated temperature and humidity levels to simulate the natural aging process. It is used to check the archival quality of various papers and paper products.

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pH Neutral - Exhibiting neither acid nor alkaline qualities. 7.0 on the pH scale.

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PVC (Polyvinyl chloride) - A plastic, often abbreviated as PVC. It is not as chemically stable as some other plastics, since it can emit damaging hydrochloric acid as it deteriorates, and therefore has limited application in the preservation of books, photographs, and paper. Some plastics called vinyl may be polyvinyl chloride.

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Ply - Layers of paper laminated together to make heavier sheets - i.e., museum board, conservation board, etc.

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Polyethylene (high- and low-density) - A chemically stable, highly flexible, transparent or translucent plastic with a low melting point. Used in preservation to make sleeves for photographic materials, when made with no surface coatings or additives.

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Polypropylene (extruded and cast) - A stiff, heat resistant, chemically stable plastic. Common uses in preservation are sleeves for photographs, slides or film; containers. Polypropylene has better clarity than polyethylene and less static charge than polyester.

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Polyvinylchloride (PVC) - Resembles polyethylene but contains volatile plasticizers that are detrimental to artifacts and are considered very unsafe.

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Preservation - Action taken to retard or prevent deterioration or damage.

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Pressure-Sensitive - An adhesive that will adhere to a surface by means of light pressure.

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Rag (Board/Paper) - Board or paper with a high rag content. A term used to describe non-wood products in the manufacturing of paper. Can consist of true rags, cotton, hemp or linen.

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Resin-Coated Paper - Printing papers employing a special base material, treated during manufacture with a plastic "resin coating" which, by limiting water absorption, allows for very rapid processing and reduces drying time. This paper is not archival.

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Slip agents - Photographically-inert substances that prevent plastic from clinging to film. Any material that does not contain slip agents is ideally suited for direct contact with film or negatives.

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Ultraviolet - The common name for the band of short wavelength, high-frequency electromagnetic radiation - bordering on the visible spectrum beyond visible violet light. Ultraviolet causes fading and structural damage to artifacts. Daylight is the most dangerous form. Also damaging are fluorescent lights.

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