Maybe the most ancient painting technique, the affresco (italian for « fresh ») is mural painting made directly on wet lime with mineral pigments diluted in water. It always has been the best way to decorate the walls of churches, palaces and cathedrals and required great technical mastery and a fast but secure execution. Its character and its esthetic are therefore deeply influenced by the surrounding architecture, the shape of the walls and the general colour sheme of the building. The fresco painting requires flat, simple and large forms and should be aiming at a decorative style. There are two ways of fresco painting: the original one, called also « fresco buono » (painting on to the wet mortar) and the « a secco » technique, that is painting on the dried plaster.
The original fresco is always made on a wall surface covered with plaster wich is made of slaked lime, sand, marble pouder and water. Lime absorbs carbonic acid gas from the air and forms a glassy skin on the surface of the painting. This skin incorporates the pigment in the plaster making it absolutely insoluble in water. The most usual proportion, even from the ancient times, of sand and lime (especially in the first coats) is always 1:3. In some ricipes the last coat is richer in lime and leaner in sand. Marble dust can also be found in the upper layers. Other materials used in ancient ricipes include straw, tow and cow hair, all used in order to lessen the danger of cracking. The quality and the proportions of the materials are very important for the succesful realisation of the work. The wall which is to be used for fresco must be absolutely dry and exposed to the air for some time.
The basic steps of the wall preparation are the following: first the roughcast (a mixture of 3 parts of coarse sand and 1 part of lime) is applied on the wall. The mortar is beeing actually thrown to the wall, from top to bottom, until the coating becomes 1,5 cm thick. After about 20 minutes, the second plaster coating may be applied on to the first. Again after about 20 minutes the third coat can be applied, which is made of 2 part of fine sand or marble grit and 1 part lime. One can paint on to this third, rough coat of plaster, especially for work out of doors. But the traditional technique requires one last plaster coating, the so called intonaco, made of 1 part sand or marble dust and 1 part lime. This ground must be smoothened with a wet plane and the it’s ready for painting. One can paint wet on wet on this ground for about 5 or 6 hours, before the intonaco dries. This means that a large scale work must be devided in to several parts: one must cover only this part of the wall that can be finished in a day. Once the day’s work is done, no changes can be made. Therefore, a very detailed preparatory drawing is required, which will be applied on the intonaco by tracing or pouncing. The outlines of the drawing will be incised in the wet plaster so that the artist will not lose the basic lines of his composition. For a very detailed work, a pounce bag can also be used filled with carcoal dust or an earth pigment (usually red ocher). The artist must have a very clear idea of his intentions before he beginns work.
One proceds by applying first the more lighter colours, which correspond to the lighter local tones of every form, and goes on with the modelling of the volumes, gradually applying the more deeper colours, painting from light to dark. The intonaco tone serves as the white of the palette, which means that one must work as with watercolour. The colours themself must be liquid and watery, but must not run down in drops. Another way of painting a fresco is the following: after laying down the contours of the composition, the artist puts down the shadows and then applies the local colour all over the form (human figure, architecture ect). Then he deepens the shadows and finally puts on the high lights. One can also prepare in advance a three tone sheme for the modelling of a one coloured object (draperies), the same way as in tempera. By adding more lime in the colours it is possible to create an impasto effect, very usefull to strenghten the lights. Over this impasto-like fresco colour one can employ glazes and give a more atmospheric effect. Nevertheless, it is important to carry out the work without mixing up differnet tecniques and procedures. Simplicity of execution always remains a basic premise for a succesful result.