Of the manner of applying Gold on a Bolus,[236] or with a Mordant,[237]
and other methods.
§ 93. _Methods of Gilding._
[Illustration:
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.