246 PAINT TECHNOLOGY AND TESTS 



is slightly alkaline or inhibitive in nature, and then topped with 

 a good weather-resisting material, such as lampblack, graphite 

 or carbon black, good results would be obtained. Further tests 

 will be made to determine the value of this suggestion. 



Panel No. 30 Precipitated Calcium Carbonate. Showed 

 more rapid destruction than Panel No. 29. 



Corrosion Adhering to Film Stripped from Panel Painted 

 with Gypsum (Calcium Sulphate) 



Panel No. 31 Calcium Sulphate. Under the paint film of 

 gypsum, rust soon appeared, showing that the film was not a 

 good excluder of moisture. Although the film remained intact, 

 rusting progressed throughout the test and considerably dark- 

 ened the color of the paint. 



Panel No. 32 China Clay. This pigment gave excellent 

 service for eighteen months. Afterwards indications of corrosion 

 were shown, and apparent breakdown of the film was indicated. 



