370 APPLIED SCIENCE 



This is commonly done by burning the old coat with a Bunsen 

 burner. The heat causes the paint to soften and to "peel" 

 or blister. It is then easily scraped off. In other cases paint 

 or varnish solvents are applied before scraping. Surfaces 

 from which old finishes have been removed must be sand- 

 papered until perfectly smooth. When the wood has been 

 laid bare, smoothed, and cleaned, it is ready for one or more 

 coats of new paint. The color selected for the first coat is 

 chosen with regard to the color of the coats that are to follow. 

 This first coat is known as the priming coat. 



The priming coat is worked well into cracks and nail holes 

 to protect such broken surfaces and is then allowed to dry. 

 After this the cracks and holes are filled with putty, to which 

 the paint adheres well. Two or more coats of the required 

 color are then applied, the number and composition of the 

 final coats depending upon the class of work. 



412. Composition of Paint. A paint consists principally 

 of two elements: (1) a body of opaque coloring matter which 

 covers the surface and which is not dissolved by water, 

 and (2) a vehicle with which the coloring matter is mixed so 

 as to be easily applied. The vehicle evaporates and leaves 

 the coloring matter deposited on the surface. In addition, 

 other substances are added to paint, such as solvents, to 

 make the paint more liquid and therefore more easily applied, 

 and driers, to hasten the hardening of the paint. 



413. Linseed Oil. The principal vehicle for most paints 

 is linseed oil, as it is the best drying oil; that is, on exposure 

 to air it absorbs oxygen and is converted into a transparent 

 resin-like mass. Sometimes other oils are used, but they are 

 all inferior in drying power to linseed oil. Raw linseed oil 



