Fresco means painting in pigments alone on to a damp fresh lime mortar. A chemical reaction takes place; calcium hydroxide (lime putty) combines with carbon dioxide (in the air) and form calcium carbonate (limestone). The pigments are locked into the lime in Buon Fresco. This technique produces the most enduring form of wall decoration. Mezzo fresco and Secco painting are additional techniques to enable the painter to continue work once the mortar starts to carbonate.
A fresco is structurally part of the fabric of the building. Because the lime mortar can "breath" moisture in the building can escape and condensation in the air can be absorbed without the usual destructive side effects to the building and painting. There is no need to varnish and therefore the problems associated with varnish, ageing and reflections are absent.
The tradition is not confined to Italy. It is seen throughout Europe and Asia. In Britain, the temples and palaces created under Roman rule always contained them. The medieval period also boasted highly colourful and decorated interiors both in secular and religious buildings but the Reformation signalled a decline in the prominence of fresco painting. Attempts to rekindle the art in the UK has not been successful a lack of expertise and conviction has meant such rebirths have been short-lived.
But now, at last, the circumstances are ripe for a revival. Its source: the growing awareness of the destructive impact of modern construction materials and methods when applied to old buildings. In recent years this greater sensitivity has seen resurgence in the use of lime mortar and with this shift the interest in fresco painting has rekindled. It has even extended to modern building sites.