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Technique

In the history of murals, several methods have been used:

A fresco painting, from the Italian word affresco which derives from the adjective fresco ("fresh"), describes a method in which the paint is applied on plaster on walls or ceilings.

The buon fresco technique consists of painting in pigment mixed with water on a thin layer of wet, fresh, lime mortar or plaster. The pigment is then absorbed by the wet plaster; after a number of hours, the plaster dries and reacts with the air: it is this chemical reaction which fixes the pigment particles in the plaster. After this, the painting stays for a long time up to centuries in fresh and brilliant colors.

Fresco-secco painting is done on dry plaster (secco is "dry" in Italian). The pigments thus require a binding medium, such as egg (tempera), glue or oil to attach the pigment to the wall.

Mezzo-fresco is painted on nearly-dry plaster, and was defined by the sixteenth-century author Ignazio Pozzo as "firm enough not to take a thumb-print" so that the pigment only penetrates slightly into the plaster. By the end of the sixteenth century, this had largely displaced the buon fresco method, and was used by painters such as Gianbattista Tiepolo or Michelangelo. This technique had, in reduced form, the advantages of a secco work.