EFFECT OF GROUND COATS ON REFLECTANCE OF COVER ENAMELS *

The problem of color variation in white cover-coat enamels has received considerable attention, but variations in color due to base coat have had little or no consideration. An attempt was made to determine the effect of the base coat by comparing color variations in opaque and superopaque enamels applied over blue, white, gray, red, yellow, and green base coats in weights ranging from 10 to 120 gm. per sq. ft. The resultant finishes were compared visually and with the aid of the Hunter multipurpose reflectometer. Over the entire range studied, the base coat was found to have a marked effect on the color characteristics of the finish coat. This is true particularly in the lower ranges of application including normal production application weights. Base coats that decreased the reflectance of the cover coat in the blue field, were found to give higher apparent opacity than those which maintained a relatively high blue reflectance.