Distemper is an aqueous paint ( can be diluted in water), for which size (glue) is used as a binder. Limestone meal or chalk - hence the name whiting- is used to make it white or as an inert pigment (filler). colored pigments can be added as desired. However, since the size remains water-soluble even after it has dried, it cannot be overpainted. The German painter Otto Mueller often used distemper applied directly to hessian sacking, which makes conservation of his paintings very difficult.