CHAPTER XIV. (XXVIII.)
Of the manner of applying Gold on a Bolus,[[236]] or with a Mordant,[[237]]
and other methods.
§ 93. Methods of Gilding.
FRESCO FROM RAFFAEL’S LOGGIE IN THE VATICAN.
It was truly a most beautiful secret and an ingenious investigation—that discovery of the method of beating gold into such thin leaves, that for every thousand pieces beaten to the size of the eighth of a braccio in every direction, the cost, counting the labour and the gold, was not more than the value of six scudi.[[238]] Nor was it in any way less ingenious to discover the method of spreading the gold over the gesso in such a manner that the wood and other material hidden beneath it should appear a mass of gold. This is how it is done. The wood is covered with the thinnest gesso kneaded with size weak rather than strong, and coarser gesso is laid on in several coats according as the wood has been well or badly prepared. When the gesso is scraped and smoothed, white of egg beaten carefully in water is mixed with Armenian bole, which has been reduced with water to the finest paste. The first coat of this is made watery, I mean to say liquid and clear, and the next thicker. This is laid on to the panel at least three times, until it takes it well all over, then with a brush the worker gradually wets with pure water the parts where the Armenian bole has been applied and there he puts on the gold leaf, which quickly sticks to that soft substance;[[239]] and when partially but not entirely dry he burnishes it with a dog’s tooth or the tooth of a wolf in order to make it become lustrous and beautiful.[[240]]
Gilding is effected in another fashion also, ‘with a mordant,’ as it is said.[[241]] This is used for every sort of material—stone, wood, canvas, metals of all kinds, cloth, and leather; and is not burnished as is the former. The mordant, which is the lye that holds the gold, is made of various sorts of drying oil pigments and of oil boiled with the varnish in it. It is laid upon the wood which has first received two coats of size. And after the mordant is so applied, not when it is fresh, but half dry, the gold leaf is laid upon it. The same can be done also with gum-ammoniac, when there is hurry, provided that the stuff is good. This is used more to adorn saddles and make arabesques and other ornaments than for anything else. Sometimes also gold leaves are ground in a glass cup with a little honey and gum[[242]] and made use of by miniature-painters and many others who, with the brush, delight to draw outlines and put very delicate lights into pictures. And all these are most valuable secrets; but because they are very numerous one does not take much account of them.