Page:An Elementary History of Art.djvu/340

 310 Painting. gilder's whitening in the medium slightly diluted with turpentine. This, when dry, produces a perfect surface — " so white that colours upon it have all the internal light of Buon Fresco, and the transparency of pure water- colours." This can be easily observed in the Arts of War. If in painting the work, any part from having been left becomes quite hard, that part can be softened with a wash of pure spike-oil, but a too frequent use of this is to be avoided. " The rationale of the painting," says Mr. Parry, " is this, that the colours in powder being incorporated with material identical with that which has already sunk deep into the pores of the wall surface, and has hardened by the evaporation of the turpentine vehicle, may be regarded as belonging to the mass of the wall itself, and not as mere superficial applications." The medium is formed slightly differently when, as in the works in Ely Cathedral, it is for use on panel, instead of stucco and similar surfaces. Mosaic painting is the art of producing designs with small square pieces of stone or glass of various colours in such a manner as to give the effect of painting. It was largely employed by the ancient Romans for pavements, and by the early Christians for the ornamentation of churches. The mosaics in the Cathedral of Ravenna are world-famous. At the present day it is chiefly an Italian art; but Russian and British artists have of late years produced some successful specimens of mosaic work. The pieces of glass which go to make up the design are techni- cally called smalts and tesserae, and are set in cement in the same way as tiles in pavement. The Italians practise two kinds of mosaic work — the Florentine, in which small pieces of stone or shell of their natural colours are used ;