Paints are dynamic systems which are in an almost constant state of change throughout their whole life. These changes are evident from the time of manufacture and througout storage when the liquid paint can undergo major rheological changes due to binder adsorption, crosslinking or, with waterborne systems, biological attack, as well as associated problems such as pigment instability. When in service the dried film also exhibits progressive changes. These occur in both surface properties by erosion, loss of gloss colour change, and also in bulk properties by, for example, embrittlement. Both are often due to structural changes within the cured film and can be due to a variety of external causes such as solar radiation, oxidation or chemical attack.