Absorption: The action by which a liquid or gas is leaked or drawn into the porous or permeable structure of a solid or fluid. This contrasts with adsorption, where the substances are simply held on the surface of the solid material. See also Adsorb, adsorption.
Accretions: Solid pieces of extraneous or foreign matter attached to the surface of artwork or an object such as dirt or food particles. Should the removal of such matter be required, great care must be exercised during the mechanical dismantling process to avoid tears, holes or similar damage. Where the artwork has any sentimental, historical or financial value a qualified Conservator ought to be consulted.
Acid: In chemistry, a compound that produces hydrogen ions (H+) in aqueous solutions. The resulting concentration and state of hydrogen ions in water is known as acidity.
Acidic paper: Depending on the process used in its production, and the materials it is in contact with, paper can be acidic, neutral or alkaline. Many new papers are acidic and although they may initially be quite strong they will rapidly lose strength if they contain strong acids. This is due to chemical reactions that break down the chain length of the cellulose, the main component of paper. When paper loses most of its strength, it is said to be brittle.
Acid-free: A technical term that describes materials, including boards and papers, that have a reading of 7 pH, or very close to 7 pH. Acid-free materials are more permanent and less likely to discolor over time. The term Archival or conservation quality more accurately describes true acid-free conservation quality matboard.
Acid migration: This refers to the contamination, or transfer of acid from an acidic material to one less so or to an acid-fee one. In picture framing this often occurs when acidic papers or boards are placed in contact with non-acidic artwork thereby staining and damaging it.
Acid rain: Rain, or precipitation, with a pH below 5.7. Caused by oxides of nitrogen and sulphur released into the air through the burning of fossil fuels for transport, heat and power. These oxides are converted into nitric and sulphuric acids and washed down in the rain. Acid rain can be particularly damaging to stone buildings, outdoor metal and stone sculpture.
Acrylic: A class of plastics known for their clear optical properties and durability. Acrylics have good resistance to the effects of sunlight and exposure to the elements over a long period of time. They do not yellow significantly or undergo significant changes in their physical properties. Acrylic sheets are used extensively for glazing in picture frames. Perspex and Plexiglas are trade names of manufactured acrylic sheeting. Acrylic resins are also widely used in binders for adhesives, paints and varnishes
Adhesive: A substance capable of bonding or gluing materials to each other by chemical or mechanical action, or both, and which may be activated by water, non-aqueous solvents, pressure, heat, cold or other means. A desirable characteristic of adhesives used in conservation is reversibility.
Adsorption: The action by which a liquid or gas is stopped or held on the surface or outside of a solid material. This contrasts with absorb and absorption, where a liquid or gas is leaked or drawn into the porous or permeable structure of a solid or fluid. See also Absorb, absorption.
Agency: In picture framing, an Agency is run by an Agent who agrees to have your picture framed but does not actually do it and merely passes the work on to a third party for a fee or commission, much like leaving your clothes to be dry-cleaned at the Newsagent. Agencies were more common in the past, but still exist, particularly in the country. It's preferable though to leave your artwork to be framed personally by the picture framer, or his~her staff, on their premises. Avoid having your artwork double-handled, loaded into trucks and shipped off to strangers who have not talked to you and may not be professional picture framers.
Alkaline buffer:
Chemicals that neutralize acids present in papers or boards as a result of manufacture or the environment. Various agents may be used as alkaline buffers but magnesium or calcium carbonate are the most common. While this is a useful method to decelerate paper deterioration, it can be damaging when in contact with other materials such as leather or older photographs.
Alpha cellulose: The insoluble part of cellulose composites when in a 17.5% solution of sodium hydroxide at 20ˇC under specified conditions. Alpha cellulose is made up mostly of cellulose but may include other materials that are insoluble under test conditions. Because the durability of papers and boards depends to some extent on the absence of non-cellulosic impurities, the determination of true cellulose-alpha cellulose-gives also indicates its stability and permanence. The term alpha cellulose in a paper or board specification generally indicates a high-quality product.
Ambrotype: A 19th century, photographic process that produced a wet collodion negative image onto a glass plate which was coated with black paper or lacquer to give a positive image. A popular photographic portraiture medium during the 1850s.
Aniline Dyes: Today this term refers to any synthetic organic dyes and pigments, regardless of source, as against animal or vegetable colouring materials, natural earth pigments, and synthetic inorganic pigments. Aniline dyes are classified according to their degree of brightness or their light fastness. Basic dyes are known for their extreme brightness, as well as for their lack of colour fastness.
Archival: An inexact term implying materials, products or processes that are durable, chemically stable, of long life and suitable for conservation purposes. The phrase is not quantifiable; no standards exist that describe how long an 'archival' material will last. Permanence and permanent are often used to mean the same thing.However, most reputable manufacturers nowadays produce non-acidic, archival-quality materials can be safely used for long-term display or storage of valuable artwork without causing or adding to degradation. These materials usually have additives that slow down deterioration caused by other factors. Archival-quality papers, cards and boards are mostly made from high-quality cellulose fibres such as those from rags. Archival-quality plastics are inert and allied adhesives are stable without acids.
ATG Tapes: Double-sided tapes used to stick mat boards and other mterials together. Usually used with an
Adhesive Transfer Gun or applicator, available at Art Supply stores.
Auxiliary support:
In picture framing, the structure to which the substratum or support is attached. In a conventional oil painting this is normally a wooden stretcher.