fresco

Mural painting technique using water‐based paint on wet plaster that has been freshly applied to the wall. The technique is ancient and widespread; some of the earliest examples (c. 1750–1400 BC) were found in Knossos, Crete (now preserved in the Archaeological Museum in Heraklion). However, fresco reached its finest expression in Italy from the 13th to the 17th centuries. One of the finest examples of fresco is the ceiling of the Sistine Chapel (1508–12) by Michelangelo, in the Vatican, Rome.

The advantage of fresco over other wall‐painting methods is that it produces an exceptionally permanent result. The colours become incorporated with the substance of the plaster, and if the process is properly carried out, are as lasting as the plaster itself. It is suitable only for dry climates, as damp causes the plaster to crumble. For this reason, fresco was never as popular in watery Venice as it was in other major Italian art centres such as Florence and Rome.

Technique
The plaster is applied to a brick or stone wall in two basic coatings, the first (arriccio), half an inch thick, to the whole wall at once; the second, finer coating (intonaco) only to that portion of the wall which it is intended to paint in any one day so that it may not be dry before receiving the pigments. In drying, a crystal surface of carbonate of lime forms over the plaster, and it is essential that the pigments should be there ready to receive this coating, which is protective to them and gives them clearness. The artist would earlier have made a full‐scale drawing of the picture, called a cartoon. This was transferred to the intonaco by holding it against the wall and either running a stylus around the outlines, indenting the plaster beneath, or dusting charcoal through a series of pin pricks along the outlines (a process known as pouncing). The cartoon was usually cut into sections of varying size, so that each could be used for a day's work. As the joins of each section of plaster remain fairly clearly perceptible, it is possible for art historians to calculate the number of days the artist spent painting the whole work. The colours, principally earths or minerals, which best resist the chemical action of the lime, are ground and mixed with pure water and applied thinly and transparently, rather darker than the desired effect because they become paler in drying. The painter must be skilled enough to work with the utmost decision and certainty, and the whole work must be previously planned with great thoroughness. If the artist made a mistake the only way to make changes was to chip away an area of plaster, replaster it and start again. Buon fresco, the true method, is distinguished from fresco secco (‘dry fresco’), painted on dry plaster. The result of the latter method was far less durable, though fresco secco was sometimes employed to add final touches to work carried out in true fresco.