112 PAINT TECHNOLOGY AND TESTS 



the comparative opacity or hiding power of the different paints 

 applied. It is well known that various pigments when ground 

 in oil differ in their hiding power in direct proportion to the 

 difference in the refractive indices of the pigments and oils used, 

 those containing high percentages of pigments such as white 

 lead and zinc oxide being superior in hiding power. After the 

 second and third coat of paint had been applied to each panel, 

 there was evident a remarkable difference in the hiding power, 

 as the black cross showed through in some cases quite clearly, 

 while in other cases it was almost completely hidden. The 

 hiding power of a paint is one of the properties which the master 

 painter looks upon as most essential, but it should, of course, be 

 accompanied in a satisfactory paint by good spreading power and 

 longevity. 



Actinic Light Tests. After the drying of all the paints, it 

 was decided that it would be of extreme interest to conduct a 

 test on the resistance of certain paints to actinic light. It is 

 well known that the ultraviolet or chemical rays of the sun are 

 most energetic in causing chemical reactions that result in the 

 early decay of certain types of paint. It was thought that the 

 disintegrating effect of these rays, as well as their effect in 

 the bleaching out of colors, might be prevented by placing 

 upon certain panels small orange colored glass slides which would 

 prevent the passing of these rays to the painted surface. The 

 slides used were five inches long and three inches wide and were 

 placed upon the middle board of certain panels, with picture 

 framing, putty, and galvanized iron tacks. The preservation of 

 the underlying surface from the sun's rays would, it was thought, 

 prevent the deterioration of the paint, and at the same time 

 preserve its original color so that it might be compared to the 

 color of the exposed portion at the time of inspection. 



Supervision of Tests. The Atlantic City tests were under 

 the constant supervision of Committee E of the American 

 Society for Testing Materials, this committee having accepted 

 the inspection of the fence. A representative was constantly 

 present throughout the work in order to see that each formula 

 received fair treatment. The actual painting work was under 

 the supervision of the writer, together with a master painter 

 representing George Butler who was chosen by the Master 

 Painters' Association of Philadelphia as the official painter of 



