Fresco. Fresco-painting is the art of painting on walls covered with plaster in such a manner that the colour and plaster unite and form a single substance. The colours are mixed with lime before being applied, and lime is also the chief ingredient in plaster, so that only those colours can be used which are able to resist its decomposing influence. These are for the most part natural earths. The use of the term "fresco" properly implies that the painting is executed on a freshly-laid surface which Is still damp; but the art of painting on dry plaster was also known to the Italians under the name fresco secco, so that we meist distinguish between this and the "true" fresco (buonfresco). Frescopainting was practised in Egypt at a very early date, and the Etruscans made use of it in decorating their tombs, which were cut out of tufa. Great progress in the art was made by the Romans, as is shown by paintings on walls in Pompeii, but it afterwards fell into disuse, and was not revived till the 12th or 13th century. The early mediaeval fresco was fresco secco, for the art of painting in - true frespo was not discovered till the latter part of the 14th century. In fresco secco the surface was sprinkled with water immediately before "painting, and the colours and the wall were allowed to dry together. It is now customary to rub the -intonaco or final coatings of plaster with pumice-stone as soon as it is dry, and afterwards to moisten it with water mixed with a little lime. The moistening takes place the evening before painting, and is repeated just before the artist sets to work. In huon fresco fresh plaster is laid on each time that the artist begins painting, and he is careful to remove any that remains when his day's work is over. Thus in this case the plaster never dries till the painting has become incorporated with it. The first step taken by the artist is to transfer the out- line of - his design from a cartoon which he has previously prepared to the damp surface of the wall, either by "pouncing" - i.e. allowing some of the powder called "pounce" to pass from a muslin bag through holes pricked in the outline on to the plaster - or by actually piercing the design with the blunt point of a stylus. There was considerable variety in the methods of carrying out this operation employed by different artists. When the outline had become implanted on the wall, the artist completed his design in accordance with a small coloured sketch, which he carried in his hand.
Fresco-painting necessarily requires great speed, as the drying of the intonaco involves fatal results. For this reason the Italian masters were often prevented from finishing their frescoes to their own satisfaction, and added further detail in distemper. Yet there are not wanting paintings - those of Masaccio, for example - which are completed in true fresco, without any admixture of distemper.