Glossary

Acid : Substance which when dissolved in water gives a solution with a pH below 7.

Acid free tissue : tissue with all acids, lignin, alum and impurities have been removed, and is neutral pH7.

Biocide : Substance used to kill plants and or other organisms.

Desiccant : A substance which removes moisture from the air and thereby lowers its humidity.

Equilibrium moisture content (EMC) : When trees are cut for timber, the moisture which was present in the living wood dries out, until the wood reaches its equilibrium moisture content; this is called seasoning.   EMC is the moisture content at which the wood is neither gaining nor losing moisture. The EMC of a particular piece of wood is dynamic, i.e. it varies according to the relative humidity of its environment.  If the relative humidity increases wood will absorb water and its EMC will rise. The absorption of water causes wood to swell. If the relative humidity decreases, the wood’s EMC drops and it shrinks.

Gesso : A solid coating made with a water binder, with glue, casein, or gelatine solution.  The dry ingredient is either whiting, chalk, or slaked plaster.  It is also used as a painting ground or as a putty or modelling material.

HEPA filter : High-efficiency particulate air filter traps particles very small particles as tiny as 0.3 microns.

Hygrometer : Instrument fo measuring humidity.

Hygroscopic material : A material which absorbs water vapour from the atmosphere at high humidities and releases it at low humidities.

Hyphae : Tube shaped fungal cells that are essentially the filaments of fungi. An individual thread is called a hypha and the network of hyphae is called a mycelium.

Microclimate : Climate produced in a small space (such as in display case) 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.

Mycelium : Hyphae combine to form a mycelium, a stringy, leathery, fluffy, or compact mat which is growth inside a substrate, e.g. soil or wood or any organic matter. In some species of fungi surface mycelium are also formed.

Mylar : Clear, stable polyester sheet used for encapsulating documents.

Oxidation : Chemical change produced by reaction with oxygen.

Patina : is a thin layer that variously forms on wooden furniture / objects sheen produced by age, wear, and polishing; or on the surface of copper, bronze and similar metals (tarnish produced by oxidation or other chemical processes); or any such acquired change of a surface through age and exposure. Patinas can provide a protective covering to materials that would otherwise be damaged by corrosion or weathering. They may also be aesthetically appealing, and are considered as evidence of use to be retained on the object.

Spores : Spores are the reproductive cells for fungi. They are often produced in great quantities, are almost always present, exhibit different shapes and colours. They are small and light weight so that they can easily be carried and spread by the wind. Under suitable conditions the spores absorb water, swell, and germinate, and the resulting germ tubes (Hyphae) initiate colonisation of the wood.

Temperature and Relative Humidity data logger : Device used to record and log the temperature and RH of the room where it is placed (e.g., in an display or storage area of inside a display case).  The times and intervals of data collection are determined by user.  The recorded information can either be downloaded manually or through internet from which the data can be accessed on line.

A picture of data loggers used in museums. (Hanwell UK, http://www.the-imcgroup.com/product/item/ml4000rht-humidity-series)

Tyvek : water resistant, gas permeable, inert polypropylene material; Tyvek is flexible, strong, soft and smooth – and cannot support the growth of fungi or bacteria. Wrapping Tyvek is excellent for use as a protective barrier and in general storage for artefacts.

Tyvek Sheet

UV (Ultraviolet) : Light which has shorter wavelength and a higher energy than visible light.  Can be very damaging to museum objects and should be eliminated whenever possible.