100 PAINT TECHNOLOGY AND TESTS 



When certain limits have been reached, however, and these 

 limits must be determined by the manufacturer and painter in 

 making practical tests, the further addition of inert pigments 

 lowers the hiding power of the paint and therefore lowers the 

 value of the paint. These remarks do not apply to artificial 

 crystalline pigments, such as precipitated whiting, which possess 

 greater hiding values than the natural pigments. 



Perry's Principles of Paint Making. Parts of the original 

 paper 1 in which Perry so clearly set forth the principles from 

 which the preceding laws were formed, follow: 



Sealing Quality or Imperviousness of the Coating. " It has 

 been emphasized that for durability and protection, the strength 

 and imperviousness of a paint coating are vital factors. The 

 protective value of the paint coating of course ceases with its 

 chalking or disintegration, but, while it is true that the protecting 

 or final life of the coating ceases with this disintegration, it is 

 also true that a paint coating has always during its true life more 

 or less porosity from the nature of the linoxin or oxidized linseed 

 oil. Therefore during its protecting life the degree of its imper- 

 viousness influences its resistance to attack upon its own life and 

 its protection of the underlying materials. The more impervious 

 the paint coating without loss of strength, the slower the oxida- 

 tion or disintegration of the paint coating itself and the greater 

 protection to the underlying material. 



" A coating of linseed oil alone is not only weak, but the 

 simplest and crudest experiments will show its porosity and this 

 porosity increases rapidly with progressive oxidation, the porosity 

 of course definitely hastening the over-oxidation or chalking. 

 In proportion, therefore, to our success in filling the voids in the 

 linseed oil film with proper pigment materials, we will in that 

 degree succeed in excluding agencies of decay, not only from the 

 mass of the paint coating itself, but also from the surface to be 

 protected. These conditions are exactly parallel in the require- 

 ments and performance of the best-made concrete, and Taylor 

 & Thompson in their work on concrete have clearly stated that 

 to obtain imperviousness there must be freedom from voids, and 

 that to obtain these conditions, the materials used must have 

 at least three determining sizes. 



1 Physical Characteristics of a Paint Coating. R. S. Perry. Michigan 

 Chapter, Amer. Institute of Architects, 1907. 



