[239]. See Note 1, ante, p. [248].
[240]. For the various processes of preparing a panel for painting and for gilding reference must be made to Cennini’s Trattato, where many technical matters are elucidated that Vasari passes over almost without notice. It must be remembered that Cennini writes as a tempera painter, while in Vasari’s time these elaborate processes were falling out of use. In his chapters 115–119, Cennini gives recipes for what he calls ‘gesso grosso’ and ‘gesso sottile.’ They are made of the same materials, ‘volterrano,’ or plaster from Volterra, which is a sulphate of lime corresponding to our ‘plaster of Paris,’ and size made from parchment shreds; but the plaster for ‘gesso sottile’ is more finely prepared. The plaster, produced by calcining gypsum, is first thoroughly slaked by being drenched with water till it loses all tendency to ‘set,’ and is then as a powder or paste mixed with the heated size. The size makes the composition dry quite hard, and Cennini speaks of its having a surface like ivory.
[241]. See Note 2, ante, p. [248].
[242]. This we should call ‘shell gold.’ It is in common use. The employment of the shell represents a very ancient tradition, for shells were the usual receptacles for pigments in late classical and Early Christian times.
[243]. This is excellent advice. The architectural character of mosaic decoration, the distance of the work from the eye, the nature of the technique and material, all invite to a broad and simple treatment, such as we find in the best mosaics at Ravenna and Rome. Modern work is often too elaborate and too minute in detail.
[244]. A modern would say that if the work be really inlaid, it should look like inlaid work, and not like something else. In the Italy of Vasari’s day however, as we have seen, painting had so thoroughly got the upper hand, that to ape the nobler art would seem a legitimate ambition for the mosaicist.
[245]. The durability of mosaic depends on the cement in which the cubes are embedded and on the care taken in their setting. The pieces themselves are indestructible but they will sometimes drop out from the wall. Hence extensive restorations have been carried out on the Early Christian mosaics at Ravenna and other places.
[246]. In his Proemio delle Vite (Opere, I, 242) Vasari explains what he means by the words ‘antique’ and ‘old.’ The former refers to the so-called ‘classical’ epoch before Constantine; the latter to the Early Christian and early mediaeval period, prior to the Italian revival of the thirteenth century.
[247]. At S. Costanza (see Note 5, ante, p. [27]) on the vault of the aisle there are decorative mosaics of the time of Constantine showing vine scrolls issuing out of vases, and classical genii gathering the grapes. Birds are introduced among the tendrils.
[248]. The mosaics at Ravenna and S. Marco, Venice, are well known. In the Duomo at Pisa, in the apse, there still remains the Saviour in Glory between the Madonna and John the Baptist, designed by a certain Cimabue, and the only existing work which modern criticism would accept as from the hand of the traditional father of Florentine painting. It may however have been another painter nicknamed ‘Cimabue,’ who worked at Pisa early in the fourteenth century. The mosaics of the Tribune of the Baptistry at Florence were executed in 1225 by Jacobus, a monk of the Franciscan Order, and this fact is attested by an inscription in mosaic which forms part of the work.