Fresco is a mural painting technique that involves painting with water-based paint directly onto wet plaster so that the paint becomes an integral part of the plaster.
Developed in Italy from about the thirteenth century and fresco was perfected during the Renaissance.
Two coats of plaster are applied to a wall and allowed to dry. On the second the design is drawn in outline. To make the painting, an area of the wall corresponding to a day’s work is freshly plastered and the design retraced joining up with the uncovered parts. This area is then painted on while still wet, using water-based paint. The paint is absorbed into the wet plaster thus making it a durable mural technique. Some touching up can be done when the plaster is dry but a whole fresco painted on dry plaster is liable to flake off.