The grinding of this pigment does not practically differ from that of dry white lead in oil, but being of a harsher texture, should be ground on stone mills, preferably buhr stones, in order to get it down to proper fineness. When sublimed lead first came into the market, it had a tendency to harden while being mixed with oil, especially when becoming heated and afterward cooling before being run through the mill. Ten pounds of oil being required to 90 pounds of the pigment in those days to form a good medium paste in oil, the remedy adopted was to grind in a mixture of 90 per cent raw linseed oil and 10 per cent cottonseed oil. At that time sublimed white lead was composed of about 86 per cent lead sulphate and 14 per cent zinc oxide. At present as sold by the Picher Lead Company it is composed of 95 per cent lead sulphate and 5 per cent zinc oxide, and is more mellow than when marketed twenty-five years ago, and as a rule of better whiteness.
When ground for the trade in paste form (which is very seldom the case, however), and kept in bulk in quantity it must not be leveled off on top with water, because it will form a very thick crust on top that is difficult to mix in oil without regrinding. When ground in oil as a base for ready mixed paints, it is usually combined with a portion of zinc oxide or hydrated lead carbonate, as well as such base pigments as blanc fixe or natural barytes, China clay, magnesium silicate (asbestine) or calcium carbonate (whiting). In this admixture it mixes and works much better than when ground in the pure state. There are a few points connected with this pigment to which we shall refer later on.