FRESCO PAINTING. A painting is said to be a fresco, or painted in fresco (sul fresco intonaco, upon the fresh coat), when it is exe cuted in water-colours upon wet plaster. Fresco is the most noble and imposing of all methods of painting. Colouring in fresco was practised by the ancients, though it has not yet been shown that they painted frescoes. Vi truvius explains the mode of preparing the walls for this species of colouring, and describes a method of varnishing them when coloured to preserve them. The earliest Italian frescoes are in the church of Assissi, in the cathedrals of Orvieto and Siena, in the Campo Santo at Pisa, and in San Miniato and Santo Spirito at Florence. These and other later frescoes are painted on different kinds of walls: in the old Gothic buildings, on ashlar walls covered with a thin coat of plaster; in more recent build ings, on brick and rubble walls ; and, in some of the most recent edifices, on lath covered with various thicknesses of plaster. The best preserved of these frescoes are on brick. There are many frescoes at Pisa, Florence, and Venice, on lath, and all are in tolerable preservation.
The method of plastering the walls for painting has been nearly uniform inmost ages. The walls of the baths of Titus at Rome are covered first with a layer about half an inch thick of coarse sand and lime ; above this, a thick layer of lime and pozzolana with an ad mixture of sand and pounded brick; the third and upper coat is of limo and pounded marble. The third loggia of the Vatican, painted by Giovanni da Udine, is much the same as this. Cennino Cennini, Alberti, and various other Italian writers, give instruction as to the mode of preparing the walls and the materials for them. The selection of the limestone to be employed in fresco-painting, both for the ground and for the white, is a matter of great importance ; it should be nearly pure carbo nate of lime, and should contain as few foreign materials as possible. Modern fresco-painters recommend the lime to be kept a much longer period than Cennini and other early writers direct. If it is used too fresh, it blisters, and sometimes turns the colours to a brownish red. The lime for the intonaco in fresco paint.
ing must not be entirely carbonated, or it would not set ; a certain degree of causticity is neces sary. The picture must be executed while the intonaco is wet or soft ; no more work therefore ought to be commenced than can be completed within the time (a few hours) that the plaster requires to harden. Numerous joints are thus necessary in a large fresco ; and a judicious painter contrives that these joints shall be identicalwith the inner outlines of the parts of the figures and their drape ries, or any other object, so as to be no disfi gurement to the work. Before laying on the intonaco the prepared ground is repeatedly wetted, until it will absorb no more ; then a thin moderately rough coat of plaster of sand and lime, is laid over as much of the wet sur face as can be painted in one day ; as soon as this coat begins to set, in about ten minutes or so, another thin coatis laid on with a wooden trowel, both layers together being scarcely a quarter of an inch thick. Upon this coat the fresco is painted. This intonaco will be fit to paint upon in about a quarter'of an hour.
The colours used in fresco painting are all ground and mixed in water, boiled or distilled ; they are chiefly earths. Lime, ochres, siena, vitriol, Verona green, cobalt, chrome,. marine, and vermilion are the chief colouring substances employed. Sufficient of each tint is kept ready for the whole picture. The brushes and pencils are made of hog's hair and otter's hair.
The method of fresco-secco, or dry fresco, is thus practised :—The plastering of the wall having been completed, the whole is allowed to dry thoroughly. Before painting, the sur face of the intonaco is rubbed with pumice stone, and on the evening of the day before the painting is to be commenced it is thoroughly washed with water mixed with a little lime; it is wetted again the next morning, and is then ready for pouncing or tracing the outline, and painting ; the wall must be kept constantly moist by means of a syringe.
Frescoes are sometimes cleaned by dry bread ; sometimes by pure water, by vinegar, and by wine. Ingenious modes have been devised of removing frescoes from walls, and transferring them to canvas.