Note 115 — NUMERICAL CATALOGUE, WITH BIOGRAPHICAL AND DESCRIPTIVE NOTES (continued 4)

These pictures, like the other Florentine works here exhibited, except 564 (which is on linen cloth attached to wood) and 276 (which is in fresco), are painted in tempera on wood. Tempera (or distemper) painting is a generic term for the various methods in which some other substance than oil was the medium. Various substances were thus used—such as gum, glue or size, flour-paste, white of egg, milk of figs. Cennino Cennini, who wrote a treatise on painting at the end of the fourteenth century, professes to give the exact method of Giotto. Egg beaten up with water was preferred by him, except where the yellowness of the mixture injured the purity of the colour. The colours thus mixed were laid on to a panel (or on to a cloth stretched over the panel) previously prepared with a smooth white ground of plaster. And finally oil or albumen was used to go over the whole surface. This was the practice in general use for all detached pictures until the middle of the fifteenth century, when what is known as "the Van Eyck method" came into vogue (see under 186).

Fresco painting is painting upon walls of wet plaster with earths of different colours diluted with water. It is so called from the colour being applied to the fresh wet surface of lime, but it is of two kinds: (1) fresco secco, when the plaster of lime has been allowed to dry on the wall and is then saturated with water before painting; this was the method in use till after Giotto's time; (2) buon fresco, when the colours are laid on to the fresh plaster before it is yet dry. (The fullest account of these various technical processes and their history is Sir C. Eastlake's "Materials for a History of Oil Painting," a review of which by Ruskin appeared in the Quarterly Review, and is reprinted in On the Old Road, vol. i.).