Driers are used to hasten the drying of paints. These are ground up in oil and are mixed in small quantities with the color; some colors, in fact, will not perfectly harden without them, but remain sticky, or, as painters term it, tacky, until sufficient dust has clung to them to render their external surface at least apparently dry; though, as can be well understood, it will remain disagreeable to the touch and much injured in color. Red lead is a good drier, but, of course, can only be used in situations or in paints where its color is not objectionable. Sugar-of-lead is, however, the best drier, but is more expensive than others. Patent driers, ground up in oil, may be purchased at the various paint stores.