172 PAINT TECHNOLOGY AND TESTS 



Pittsburg, which in other respects had deteriorated the panels 

 to a greater extent than at Atlantic City, did not have the extreme 

 action in causing checking that the Atlantic City atmosphere 

 seemed to have effected. 



Results on Combination Pigment Paints. It will be noticed 

 that the checking on most of the combination pigment paints 

 made of lead, zinc, and inert pigments, was moderate, and in 

 many cases of a fine order. It has been observed that the 

 percentage of zinc oxide in a paint is not always a criterion upon 

 which future checking may be judged. Nor could it be said 

 that the checking is dependent upon the percentage of basic 

 carbonate-white lead added to the paint. However, it appears 

 that scientific blending of the various pigments, with regard to 

 their physical properties in oil, such as their strength and elastic 

 limit, develops the greatest resistance to both cracking and 

 checking. Elasticity is vital, but strength must be combined 

 therewith in order to prevent disruptions of the paint coating. 

 Paint films made of certain inert pigments, when tested on the 

 filmometer, were relatively high in strength, but relatively low 

 in elasticity. Such pigments, when used in large percentage, 

 form coatings which are hard and apt to crack. The use, how- 

 ever, of these pigments in moderate percentages seems very 

 beneficial in overcoming the effect of using an excessive per- 

 centage of white lead, or of zinc oxide. 



Results on White Lead Paints. The maximum checking 

 was observed on the basic carbonate-white lead panels, the size 

 of the checks in some cases being several times larger than those 

 on the other panels. 



On some of the basic carbonate-white leads the checking was 

 of a very peculiar nature, consisting of very broad fissures in 

 the paint coating, disclosing the wood surfaces beneath. The 

 type of checking existing was also distinct in its structure, being 

 hexagonal in shape. One of the most marked features shown 

 by the basic carbonate-white lead films was the extreme rough- 

 ness of their surfaces. This roughness is most likely due to" the 

 excessive chalking which had taken place. 



Results on Silica and Barytes Paints. The checking of 

 paints very high in silica resolved itself into fine hair-like lines 

 which are generally lateral to each other, and indicate a cracked 

 appearance. The checking of paints containing very high per- 



