The support should be even, absorbent, and of a shade that would enhance the colors used. 32 An abraded surface promoted adhesion of color for copper or other metal supports, and these might be sanded or roughened before priming layers were applied. 33 Oil colors on canvas might require up to half a dozen underlayers of sizing gessoes, dead colorings, and other primings.    From Wordnik.com.  [The Creation of Color in Eighteenth-Century Europe] Reference