PAINTS, DYES, AND VARNISHES 



vehicle. But much more important are the "drying- 

 oils." Of these drying-oils linseed oil is of most import- 

 ance to the painter more important, in fact, than all 

 the other vehicles combined. 



By a "drying-oil" we mean one that, when exposed 

 to the atmosphere, forms a thin, tough film, insoluble 

 in water, and not acted upon readily by any chemicals 

 that are likely to come in contact with it. The number 

 of such oils is very small in comparison with the num- 

 ber of oily substances, of which olive oil may be taken 

 as a typical example of a non-drying oil. A thin film 

 of this oil spread upon a surface of glass, let us say, does 

 not tend to form a hard film and lose its peculiar oily 

 quality, even after weeks of exposure to the atmosphere ; 

 whereas under similar conditions a film of linseed oil 

 would be converted into a hard, impervious layer, in 

 a matter of twenty-four hours. Olive oil, therefore, and 

 all the other non-drying oils, are useless as paint 

 vehicles. 



For special purposes several other drying-substances 

 besides the oils are used for pigment vehicles, among the 

 most used of these being turpentine, benzoline, shale 

 spirits, benzole, coal-tar naphtha, wood alcohol, alcohol, 

 and water. But all of these must be regarded as strictly 

 of secondary importance to the drying-oils, although 

 for special purposes they are indispensable. 



Of the drying-oils there are, besides linseed oil, 

 poppy-seed oil, firseed oil, weld-seed oil, hempseed oil, 

 tobacco-seed oil, menhaden oil, walnut oil, and Chinese 

 wood oil. But all these together play a very insignificant 

 part as paint vehicles in comparison with linseed oil, 



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