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Acid Substance which when dissolved in water gives a pH below 7.
Acid-free Term used to describe a neutral or slightly alkaline pH.
Albumen White of egg. Emulsion layer in most 19th century photo prints.
Alkali Substance which when dissolved in water gives a solution with a pH above 7.
Ambient conditions Natural prevailing conditions within an area or location.
Biocide Substance used to kill plants and/or other organisms.
Bleed Staining normally on paper and textiles when water or solvents are applied to dyes, etc.
Blueing Colouring of iron metal either by chemical means or by heating.
Bronze disease Corrosion of bronzes producing pustules of bright green spots on the surface (not a patina).
Carcinogen Cancer producing substance.
Collagen Protein found in bones.
Collodion A solution of pyroxylin in ether, used in photography and surgery.
Crizzled A condition of some glassware which is usually identifiable as a network of minute fractures. This unstable condition is not always visible to the naked eye.
Delamination Separating of layers of an objects or substance (see Exfoliation).
Desiccant A substance which removes moisture from the air and thereby lowers the relative humidity.
Direct light Daylight or artificial light source which falls directly on an object.
Efflorescence Crystallisation of salts on the surface of an object exposed to air or low relative humidity.
Ethnographic Material relating to people and/or cultures.
Exfoliation Coming off in scales or layers.
Fibrils Miniature fibres or strands of fibres.
Foxing Red-brown spots that appear on paper, prints, watercolours, etc. No certain cause is known although mould and impurities are the most likely.
Friability The tendency of a material to crumble into a fine sand or powder.
Gelatin Substance derived from animal skins commonly used in cooking and photography.
Gesso  A solid coating made with a water binder, either glue, casein, or gelatin solution. The dry ingredient is either whiting, chalk, or slaked plaster of Paris. Used as a painting ground or as a putty or modelling material. In the latter case it is made into a stiffer, plastic paste.
Hygrometer Term used to describe an instrument for measuring humidity.
Hygroscopic material Material which absorbs water vapour from the atmosphere at high relative humidity levels and releases it at low relative humidity levels.
Hyphae Filaments of fungi; strand-like.
Infra-red (IR)  Light having a longer wavelength and lower energy than visible light. It produces a heating effect when it shines on an object. Sometimes referred to as radiant heat.
Inhibitor A substance which slows down the rate at which a particular chemical reaction occurs. Generally refers in this text to substances which slow down the attack of acids on metal.
Keratin Sulphur-containing protein forming the basis of horns, nails, hair, etc.
Micro-climate Climate produced in a small space (such as in plastic bag, display case and like) which may be quite different from the climate in the rest of the room.
Microcrystalline  A substance composed of crystals which are very much smaller than normal.
Miscible Liquids which are capable of being mixed together. For example, alcohol and water are miscible but oil and water are immiscible.
Oxidation Chemical change produced by a reaction with oxygen or the same change produced by other means.
Oxidising agent Any substance which is capable of causing oxidation.
Patina  The ‘skin’ or layer of corrosion products which forms on the surface of metal artefacts. The term is most commonly used in reference to bronze and copper objects.
Photochemical Damage which is caused or accelerated by light (UV, visible, or IR) falling
degradation on an object.
Polymerise The joining together of a large number of small molecules (monomer units) to form a few much larger molecules (polymers).
Precipitation  The opposite process to dissolution; the formation of two separate phases from one phase. For example, when air temperatures fall the relative humidity increases until it reaches 100 %. If the temperature falls further the air can no longer contain all the water vapour and the excess precipitates as droplets of water (dew, rain or snow).
Reagent  Substance used to cause a chemical reaction or to detect another substance.
Refractive index The extent to which light rays are bent when they pass through the material.
Repatinate  The formation of a replacement patina on an object. Generally done either to improve the appearance and/or to protect metal.
Sherds Fragments of ceramic which result when a vase or other object is broken.
Silica gel   A crystalline substance that is used to extract moisture from the air.
Thermohygrograph Instrument for measuring temperature and relative humidity and recording it on a graph, usually over seven days or one month periods.
Ultra-violet (UV)  Radiation that has a shorter wavelength and a higher energy than visible light. Can be very damaging to museum objects and should be eliminated whenever possible.
Vitrify To heat to the point of glass formation.
White light Light giving the same appearance to objects as does natural sunlight, but preferably without the ultra-violet and infra-red components of natural light.
W/V Weight to volume ratio. Used to specify the concentration or strength of a solution by specifying the weight of a substance dissolved in a particular volume of another substance.
W/W   Weight to weight ratio. Used to specify the concentration or strength of a solution by specifying the weight of a substance dissolved in a particular weight of another substance.
X-ray diffraction   A process in which a beam of X-rays is passed through substance. The substance scatters the X-rays at various angles and by recording these scattered X-rays the arrangement of atoms within the substance can be determined and its chemical structure determined.