268 GILDING. 



easier spread ; but when the surface of the metal 

 is plain, the amalgam may be directly applied to it. 

 The metal required to be gilt is first rubbed over 

 with a little aqua-fortis, by which the surface is 

 cleaned from . any rust or tarnish that might pre- 

 vent the union of the two metals. The amalgam, 

 being then equally spread over the surface by 

 means of a brush, the mercury is evaporated by a 

 heat just sufficient for that purpose; for if it be 

 too great, part of the gold may also be expelled, 

 and part of it will run together, and leave some of 

 the surface of the metal bare. While the mercury 

 is evaporating, the piece is to be from time to time 

 taken from the fire, that it may be examined ; that 

 the amalgam may be spread more equally by 

 means of a brush ; that any defective parts of it 

 may be again covered, and that the heat may not 

 be too suddenly applied to it. When the mercury 

 is evaporated, which is known by the surface be- 

 coming entirely of a dull yellow colour, the metal 

 must then undergo other operations, by which the 

 fine gold colour is given to it. 



First, the gilded piece of metal is rubbed with 

 a scratch-brush (which is a brush composed of 

 brass-wire,) till its surface is made smooth ; then it 

 is covered over with a composition called gilding 

 war, and is again exposed to the fire till the wax 

 be burnt off. This wax is composed of bees-wax, 

 sometimes mixed with some of the following sub- 

 stances, red ochre, verdigris, copper scales, alum, 

 vitriol, borax ; but according to Dr. Lewis, the 

 saline substances are sufficient, without any wax. 



By this operation the colour of the gilding is 

 heightened ; and this effect seems to be produced 

 by a perfect dissipation of some mercury remain- 

 ing after the former operation. 



