33 2 PAINTS AND PAINTING 



rosin and turpentine, benzine, or rosin oil. These driers can be made 

 for very much less than the price of good linseed oil, and are used as 

 adulterants ; the more of the drier that is put into the paint, the quicker it 

 will dry and the poorer it becomes. Japan drier is often used with raw oil, 

 and when this or any other drier is added to raw oil in barrels, the oil 

 is said to be "boiled through the bung hole." 



Boiled linseed oil is made by heating raw oil, to which a quantity 

 of red lead, litharge, sugar of lead, etc., has been added, to a temper- 

 ature of 400 to 500 degrees Fahr., or by passing a current of heated air 

 through the oil. Heating linseed oil to a temperature at which merely 

 a few bubbles rise to the surface makes it dry more rapidly than the 

 unheated oil ; however, if the boiling is continued for more than a few 

 hours the rate of drying is decreased by the boiling. Boiled linseed oil 

 is darker in color than raw oil, and is much used for outside paints. It 

 should dry in from 12 to 24 hours when spread out in a thin film on 

 glass. Raw oil makes a stronger and better film than boiled oil, but 

 it dries so slowly that it is seldom used for outside work without the 

 addition of a drier. 



Lead. White Lead (hydrated carbonate of lead specific grav- 

 ity 6.4) is used for interior and exterior wood work. White lead forms 

 an excellent pigment on account of its high adhesion and covering 

 power, but it is easily darkened by exposure to corrosive gases and 

 rapidly disintegrates under these conditions, requiring frequent re- 

 newal. It does not make a good bottom coat for other paints, and if 

 it is to be used at ajl for metal work it should be used over another paint. 



Red Lead (minium; lead tetroxide specific gravity 8.3) is a 

 heavy, red powder approximating in shade to orange; is affected by 

 acids, but when used as a paint is very stable in light and under ex- 

 posure to the weather. Red lead is seldom adulterated, about the only 

 substance used for the purpose being red oxide. Red lead is prepared 

 by changing metallic lead into monoxide litharge, and converting this 

 product into minium in calcining ovens. Red lead intended for paints 

 must be free from metallic lead. One ounce of lampblack added to one 

 pound of red lead changes the color to a deep chocolate and increases the 



