906 RESINS. 



RESINOUS VARNISHES. 



Varnishes are made by dissolving resins in alcohol, or oil of 

 turpentine, or in a mixture of oil of turpentine and a drying oil. 

 These solutions, when spread upon a surface, evaporate, and 

 leave it covered by a thin coating of the resin. To diminish 

 the brittleness of spirit varnishes, a small quantity of Venice 

 turpentine is added, which gives the coating of varnish a certain 

 tenacity, or a little linseed oil, either alone or mixed with oil of 

 turpentine. 



The least coloured varnish is that from copal, which is gene- 

 rally prepared by melting that resin, mixing it while hot with a 

 little drying oil, and adding gradually to the mixture oil of tur- 

 pentine, in quantity equal to the resin. 



Lac varnish or lacker applied to articles of brass, is made by 

 heating together : 



8 parts of shell lac 

 4 parts of sandarach 

 1 part of Venice turpentine 

 4 parts of pounded glass 

 60 parts of alcohol. 



The use of the pounded glass is simply to assist the solution 

 of the pounded resin by preventing it from agglomerating into a 

 mass, or sticking to the bottom of the vessel. This is an excel- 

 lent varnish, but has a brown colour. 



The varnish usually employed to cover oil paintings, maps 

 and engravings, is made of: 



24 parts of mastich 



3 parts of Venice turpentine 



1 part of camphor 

 10 parts of pounded glass 

 72 parts of oil of turpentine * 



The paper ought to be covered by a solution of isinglass, and 

 dried, before the application of this varnish, which otherwise will 

 sink into the paper, and make it transparent. 



