S44 VARNISHING. 



managed, the spirit of sal ammoniac will be seen 

 gradually to descend from the mixture, and attack 

 the copal, which swells and dissolves, except a very 

 small quantity which remains undissolved.' 



It is of much consequence tliat the vessel should 

 not be opened till some time after it has been per- 

 fectly cold. It has happened, on uncorking the 

 vessel, when it v/as not warm enough to affect the 

 hand, that the whole of the contents were blown 

 with violence against the ceiling. It is likewise 

 important, that the spirit of turpentine should be 

 of the best quality. The turpentine bought at the 

 colour-shops seldom answers ; it should be had 

 from Apothecaries' hall. 



This varnish is of a rich deep colour, when 

 viewed in the bottle, but seems to give no colour 

 to the pictures it is laid on. If left in the damp, 

 it remains tacky, as it is called, a long time ; but 

 if kept in a warm room, or placed in the sun, it 

 dries as well as any other turpentine varnish ; and 

 when dry, it appears to be as durable as any other 

 solution of copal. 



Spirit Varnishes, 



When resins are dissolved in alkohol, com- 

 monly called spirits of wine, the varnish dries very 

 speedily, but is subject to crack. This fault is 

 corrected by adding a small quantity of oil of tur- 

 pentine, which renders it brighter, and less brittle 

 when dry. 



To dissolve Gum Copal in Spirits of Wine. 



Dissolve half an ounce of camphor in a pint of 

 alkohol, or spirits of wine ', put it into a circulat- 



