Cerium (Rare earth) is a primary drier, promotes polymerization and imparts through drying property. In alkyd based varnishes Cerium is more active as compared to lead. In contrast with lead driers, Cerium does not cause turbidity in oils and alkyd based varnishes. It has a synergistic effect when used in combination with Cobalt resulting in the need for using a lower percentage of Cobalt and thereby offering an economy. In air-drying white colourless or clear or pastel shades care must be taken to predetermine the quantity required to obtain satisfactory drying in order to avoid yellowing. As a replacement to lead, Cerium finds use in lead- free composition and where sulphur-containing pigments are used. It also resists atmospheric hydrogen sulphide stain.