[229]. Cennini in his 67th chapter gives directions for preparing the mixed colour he calls verdaccio. It was a compound of white, dark ochre, black and red.
[230]. The principle of sgraffito-work, that is the scratching through a thin superimposed coat to bring to view an under layer of a different colour, seems to have been established first in pottery making, and in this connection the Italians called it ‘Sgraffiato.’ The adoption of the process for the decoration of surfaces of plaster or cement was an innovation of the Renaissance, and Vasari appears to have been the first writer who gives a recipe for it. According to his account in the Lives, it was a friend of Morto da Feltro, the Florentine Andrea di Cosimo, who first started the work, and Vasari describes the process he employed in phrases that correspond with the wording of the present chapter (Opere, ed. Milanesi, V, 207). A modern expert describes the process as follows: ‘A wall is covered with a layer of tinted plaster, and on this is superimposed a thin coating of white plaster. The outer coat is scratched through, and the colour behind it is revealed. Then all the white surface outside the design is cut away, and a cameo-like effect given to the design. This is the art of Sgraffito as known to the Italian Renaissance’ (Transactions, R.I.B.A., 1889, p. 125). The process dropped out of use after a while, but was revived in Germany in the middle of the nineteenth century, mainly through the agency of the architect Gottfried Semper, the author of Der Stil. It is sometimes used in our own country both on monumental and on domestic buildings, and as it is simple and cheap and permanent it is well fitted for modern use in our climate. The back of the Science School in Exhibition Road, S. Kensington, was covered with sgraffiti by the pupils of the late F. W. Moody about 1872. They would be the better now for a cleansing with the modern steam-blast.
[231]. See the Notes on ‘Enriched Façades,’ and ‘Stucco “Grotesques,”’ at the close of the ‘Introduction’ to Painting, postea, pp. 298, 299.
[232]. This passage presents some difficulty. It runs ‘Dunque, quelle che vanno in campo bianco, non ci essendo il campo di stucco per non essere bianca la calce, si dà per tutto sottilmente il campo di bianco.’ Vasari seems to have in his mind the difference between ordinary plaster made, as he has just described, of ‘lime mixed with sand in the ordinary fashion,’ which would not be white, and what he calls ‘stucco,’ by which term is probably meant the finer plaster made of white lime from travertine and marble dust. Ordinary plaster has accordingly to be coated with white before the work begins.
[233]. Examples of this whimsical style of decoration are abundant in the Pompeian wall paintings, and the mind of Vitruvius was much exercised about their frivolity and want of meaning (De Architectura, VII, v).
[234]. Vasari is not very clear in his account of these methods of work, but it is enough to know that both by the ancients, and at the time of the Renaissance, colour was used largely in connection with these reliefs, and the combination could of course take several forms. In the loggia of the Villa Farnesina, where Raphael worked with his assistants, there are painted panels in fresco framed in mouldings of stucco, modelled plaster figures in white against a coloured ground, coloured stuccoes against coloured fields, and tinted bands separating the framed plaster medallions. The same kind of work is found in the Loggie of the Vatican, the Doria Palace at Genoa, and other localities innumerable. Plate XII shows a characteristic section of the decoration of the Vatican Loggie.
[235]. As in the work described at the close of ch. XII (the beginning of the present section).
[236]. The word ‘bolus’ is derived from the Greek βῶλος, a lump or clod, and means, according to Murray’s Dictionary, a pill, or a small rounded mass of any substance, and also a kind of reddish clay or earth, used medically for its astringent properties, that was brought from Armenia, and called by the pharmacologist ‘bole armeniac.’ Its use in the arts is due to its unctuous character, which made gold adhere to it. See below. In mediaeval illuminations a ‘bolus’ or small lump of a properly prepared gesso is generally laid on the parchment where gold is to come, so that the raised surface may give the polished metal more effect. The gold over the bolus was always burnished. It may be noticed that our word ‘size’ is really ‘assise,’ the bed or layer under gilding, for which a gluey substance was suitable.
[237]. A ‘mordant’ as the word implies is some corrosive liquid, such as is used by dyers to bite into the fabric and carry in with it the colouring matter. The word is also employed, as in this passage, for a glutinous size used as ground for gilding, such as the modern decorator’s ‘gold-size.’ Gold laid in this way has a ‘mat’ surface.
[238]. The scudo was worth in Tuscany about four-and-sixpence of our money. In Florence its value was a little greater.