142 PAINT TECHNOLOGY AND TESTS 



maintained under acid conditions. The acidity of the Pittsburg 

 atmosphere, caused by the large amount of acid gases which are 

 being poured into the air, day in and day out, and which are 

 constantly condensing on the surface of structures, may account 

 for the better preservation of these reds. 



" It was noted that the para reds which were applied to panels 

 prime coated with white lead seemed to be brightening in color 

 and seemed to be gradually working over toward a lightening 

 which may in the future show a pinkish tint. 



" Report on Greens. The bronze green is in most excellent 

 condition and shows an absence of the mildew appearance which 

 was observed at Atlantic City. 



" The chrome green is standing up exceedingly well, there 

 being practically no change whatsoever in the color since it was 

 exposed. 



" Best Base for Blues. An inspection of the blues showed 

 that those which gave the greatest permanence and the least 

 amount of fading were applied in combination with either Sub- 

 limed White Lead (Basic Sulphate-White Lead), or zinc oxide, 

 while those blues which were applied in combination with Basic 

 Carbonate-White Lead showed marked failure and were com- 

 pletely bleached out, due, of course, to the alkaline nature of 

 the corroded white lead; prussian blues being transformed by 

 alkalies to a white compound. 



" Superior Value of Composite Formulas. Some of the mixed 

 leads, or so-called graded leads, which are combinations of white 

 leads with other high-grade pigments and containing some inert 

 pigments, were not deteriorated so far as the white lead formulas, 

 and the general conclusion was that they were upward of six 

 months behind the deterioration of the straight white leads, and 

 this was confirmed by the presence of moderate chalking, showing 

 an excellent repainting surface and a better thickness and condi- 

 tion of the paint coating. 



" The same conclusions which were reached at Atlantic City, 

 as to the best method of shellacking, obtained also on the Pitts- 

 burg Fence, namely, that application of the shellac to the wood 

 previous to the first coat is the better method. 



" Analysis of Paints. At the time of the painting of the fence 

 a sample of each paint was placed in small friction top cans, 

 carefully labeled, and sent to the Carnegie Technical Schools' 



