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,866 known as “leucophoron:” what this last is, and how it is prepared, we shall state on the appropriate occasion.867 The most convenient method for gilding copper would be to employ quicksilver, or, at all events, hydrargyros;868 but with reference to these substances, as we shall have occasion to say when describing the nature869 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.870 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 already871 mentioned us belonging to lead with reference to gold.