CHAP. 20.—THE METHOD OF GILDING.
On marble and other substances which do not admit of being
brought to a white heat, gilt is laid with glair of egg, and on
wood by the aid of a glutinous composition,[1] known as "leucophoron:"
what this last is, and how it is prepared, we shall
state on the appropriate occasion.[2] The most convenient method
for gilding copper would be to employ quicksilver, or, at
all events, hydrargyros;[3] but with reference to these substances,
as we shall have occasion to say when describing the nature[4] of
them, methods of adulteration have been devised. To effect this
mode of gilding, the copper is first well hammered, after which
it is subjected to the action of fire, and then cooled with a
mixture of salt, vinegar, and alum.[5] It is then cleansed of all
extraneous substances, it being known by its brightness when
it has been sufficiently purified. This done, it is again
heated by fire, in order to enable it, when thus prepared, with
the aid of an amalgam of pumice, alum, and quicksilver, to
receive the gold leaf when applied. Alum has the same property
of purifying copper, that we have already[6] mentioned
as belonging to lead with reference to gold.
1. "Without entering into any research respecting the minerals employed for this cement, called 'leucophoron,' one may readily conceive
that it must have been a ferruginous ochre, or kind of bole, which is still
used as a ground. Gilding of this kind must have suffered from dampness,
though many specimens of it are still preserved."—Beckmann's Hist. Inv.
Vol. II. p. 294. Bohn's Edition.
2. B. xxxv. c. 17.
3. Literally, "fluid silver." "The first name here seems to signify
native quicksilver, and the second that separated from the ore by an artificial
process." Beckmann's Hist. Inv. Vol. II. p. 72.
4. In Chapters 32 and 41 of this Book.
5. As to the identity of the "alumen" of Pliny, see B. xxxv. c. 52.
6. In the preceding Chapter.