Materials. 307 Easel pictures, as they are called (i. e. movable oil paintings), occupy a kind of intermediate position between perishable paper drawings and mural paintings. Fresco-painting. — The ancients were acquainted with several modes of painting on wall surfaces, and discovered at a very remote age that any colouring substance mixed with plaster when wet would remain in it when dry. The term fresco — an Italian word, signifying fresh — has been given to paintings made upon plaster still wet or fresh. In fresco painting a design is first sketched the full size of the subject to be represented, and a careful study in colour is made on a small scale. The pigments are generally earths or minerals, as other substances would be injured by the action of time. The ground painted on is the last coating of plaster, which is laid on just before the artist begins his work. He first transfers the exact outlines of his composition to the wet smooth surface by pricking them through transfer-paper with some sharp instrument. The actual painting has to be done very rapidly, and the greatest skill and decision are necessary, as no subsequent alteration can be made. Any portions of plaster unpainted on when the day's work is done are cut away. The process just described is called fresco buono, to distinguish it from an inferior kind of mural painting paradoxically known as fresco secco, in which the colours mixed with water are laid on to the dry plaster. Pictures in fresco secco are in every respect inferior to those in fresco buono. A few years ago great importance was attached to the discovery by Dr. Fuchs of a substance called water-glass (soluble alkaline silicate), which appeared to possess the property of giving brightness and durability X 2
