yellowing
Discolouration that affects the whole surface of an item – e.g. an entire sheet of newspaper or the entire varnish layer of a painting - and that has a yellow tinge.
warping
Results in changes to the object’s original dimensions; often occurs along lines of stress within the material. More often applied to wood and other more solid constructions than to thin materials such as paper. See also distortion.
vinegar syndrome
A condition of acetate film decay characterised by shrinkage, embrittlement and the generation of acetic acid vapour, which smells like vinegar.
tidemark
Localised discolouration that forms at the edges of liquid stains, on drying. The staining material may have been within the liquid or the object; both will be carried to the edge of the evaporating liquid and “pinned” in place by surface tension, causing the characteristic pattern.
tenting
Delamination of paint layers above a crack or network of cracks, where the delaminating material lifts upwards to resemble a peaked tent.
tear
Separation between or across the fibres of canvas, paper or textile objects, usually beginning at the edge of the object and often following areas of weakness (e.g. folds) and initiated by physical damage.
tarnish
Discolouration of a metal surface due to the formation of a thin film of oxide, sulphide or some other corrosion product. Used most often to describe the black corrosion product that forms on silver.
sweating
In plastics, where various additives (e.g. plasticisers, stabilisers and fire retardants) leach out of the plastic and cause the surface to become moist and tacky.
surface dirt
Dirt and grime transferred to a surface through air currents, humidity and handling. Some surface dirt can be greasy or ingrained, making it difficult to remove.
stain
A localised discolouration, often caused by splashes of liquid or by contact with an acidic material, such as an adhesive or ink.