What is a powdered substance, as charcoal, bituminous coal, ect., applied to the face of a mold, or mixed with the sand that forms it, to give a fine smooth surface to the casting called?

facing — (Founding) A powdered substance, as charcoal, bituminous coal, ect., applied to the face of a mold, or mixed with the sand that forms it, to give a fine smooth surface to the casting. (Webster's 1913.)