240 VARNISHING. 



These agents are of such a nature as either to 

 dry up and become hard, or to evaporate and fly 

 off, leaving the resin fixed behind. 



Varnishes should be carefully kept from dust, 

 and in very clean vessels: they should be laid as 

 thin and even as possible with a large flat brush, 

 taking care to lay the strokes all" one way. A warm 

 room is best for varnishing in, as cold chills the 

 varnish, and prevents it from laying even. 



Varnishes are polished with pumice-stone and 

 tripoli. The pumice-stone must be reduced to a 

 very fine powder, and put upon a piece of serge 

 moistened with water; with this the varnished sub- 

 stance is to be rubbed equally and lightly. The 

 tripoli must also be reduced to a fine powder, and 

 put upon a clean woollen cloth, moistened with 

 olive-oil, with which the polishing is to be per- 

 formed. The varnish is then to be wiped with soft 

 linen, and, when quite dry, cleaned with starch, or 

 Spanish- white, and rubbed with the palm of the 

 hand, or with a linen cloth. 



Ftit Oil Varnish. 



Fixed or fat oil will not evaporate ; nor will it 

 become dry of itself. To make it dry, it must be 

 boiled with metallic calces or oxides. Litharge is 

 generally used for this purpose. Oil so prepared is 

 called drying-oil. To accelerate the drying of oil 

 varnish, oil of turpentine is added. 



Gum-copal, and amber, are the substances prin- 

 cipally employed in oil varnishes ; the copal being 

 whitest, is used for varnishing light, the amber for 

 dark colours. 



It is best to dissolve them 'before mixing them 

 with the oil; because, by this means, they are in 



