250 PAINT TECHNOLOGY AND TESTS 



Panel No. 39 Zinc Chromate. This panel is in condition 

 similar to Panel No. 34, presenting a perfect appearance, with 

 decided maintenance of color, elasticity of film, and freedom from 

 any bad characteristics. It has proved to be one of the highest 

 type rust inhibitive pigments. 



Panel No. 40 Zinc-and-Barium-Chromate. Although the 

 color of this pigment is not very pleasing, it has proved itself to 

 be the equal of zinc chromate in its protective value. 



Panel No. 41 Chrome Green. In excellent condition. 

 Presents an appearance similar to Panels Nos. 34 and 39. 

 Its surface is perfect and will doubtless give service for many 

 years. 



Panel No. 44 Prussian Blue. This panel stands forth as the 

 most wonderful moisture-excluder in the whole test, its sur- 

 face presenting an appearance similar to a varnished plate, even 

 after three years "exposure. Action between the pigment and the 

 oil, resulting in the formation of iron linoleate, may account for 

 this property. 



Panel No. 45 Prussian Blue. In same condition as Panel 

 No. 44. 



Panel No. 48 Ultramarine Blue. Soon after this test was 

 exposed, early vehicle decay and excessive chalking were observed. 

 The admittance of moisture may have caused the formation of 

 acid with the sulphur content of the pigment, iwhich would 

 account for the rapid corrosion which followed. || is of a pro- 

 nounced stimulative type. The effect of stimulative under- 

 coatings is well shown on some special plates on the fence, which 

 when received were not pickled before painting, but had upon 

 their surfaces the ordinary coating of mill scale. Over this had 

 been stencilled in a triangular form the trade mark of the manu- 

 facturer. The stencilling material was made of ultramarine 

 blue. When these plates were painted with some of the special 

 paints, and exposed, the stimulative nature of the ultramarine 

 blue began to assert itself, and within a short time, wherever the 

 stencil marks were located, signs of rust began to appear through 

 the coatings of top paint which had been applied. Corrosion 

 under these stencil marks became so great that the trade mark 

 was plainly outlined in letters of rust. This would seem to be 

 final proof that pigments of a stimulative nature should never be 

 used for the priming of iron and steel. 



