Page:Landscape Painting by Birge Harrison.djvu/155

PIGMENTS that is required is a little care and intelligence in the selection of the pigments. Lead is the one dangerous factor. If we were willing to take from the palette the white lead and the chromes, which have also a lead basis, we could use almost all the other pigments with impunity. But our only substitute for white lead is zinc white, which has the disadvantage of being so extremely brittle when hard-dry, that it cracks when the canvas is rolled, or under the action of extremes of heat and cold. The danger from lead is its strong affinity for sulphur, and the unfortunate fact that sulphide of lead is a blackish brown. Therefore when any of the colors containing sulphur (such as vermilion and the cadmiums) are mixed with either white lead or the chromes, we are sure to evolve the deadly sulphide, and there [115]