PAINTS, DYES, AND VARNISHES 



undercooking and overcooking are likely to be harm- 

 ful to the finished product. Undercooked varnish, in 

 which the resin and oil have not combined thoroughly, is 

 likely to disintegrate quickly when applied to a surface 

 exposed to air and light. Overcooked varnish is likely 

 to be darker in color and requires more turpentine for 

 thinning. As this evaporates when the varnish is ap- 

 plied, it leaves a thinner permanent covering, and af- 

 fords less protection. 



The final process of varnish manufacture is that of 

 adding the requisite amount of turpentine to the oil- 

 and-resin solution. This amount has been accurately 

 determined beforehand, and when the liquid in the 

 kettle has cooled sufficiently it is added slowly with 

 constant stirring. If this is done in the neighborhood 

 of a flame, conflagrations are likely to occur, as the heat 

 from the contents of the kettle volatilizes a certain 

 amount of the turpentine, which is very inflammable. 

 Carelessness in this matter is a not unusual source of 

 conflagrations in varnish-making establishments. 



Benzine serves the same purpose in thinning varnish 

 as turpentine, and as its cost is only about one-fifth 

 that of the turpentine, it is used in cheap varnishes. 

 It is very much more volatile than turpentine, and this 

 is a disadvantage where fine work is desired. For 

 this evaporation is so rapid that the varnish "sets" 

 almost immediately, before the ridges left by the brush 

 have time to be obliterated by the spreading and equaliz- 

 ing process as in the case of the slower-drying turpentine 

 varnish. 



The quality of the finished product depends upon 



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