mold-facing

from The Century Dictionary.

• noun In iron- and brass-founding:
• noun A thin coating of finely pulverized material dusted upon the inside faces of molds, to insure smooth outside surfaces on the castings. For iron, powdered charcoal and milldust, and sometimes plumbago, are used.
• noun A wash of plumbago and water laid on the faces of a mold by gentle manipulation with a soft brush, and allowed to dry before the cast is made.