6. PROCESS OF PRODUCING A HIGHLY PERMEABLE CALCIUM SULFATE METAL-CASTING MOLD WHICH COMPRISES MIXING CALCINED GYPSUM AND A FOAMING AGENT WITH WATER TO YIELD A SLURRY, AGITATING SAID SLURRY TO GENERATE GASEOUS BUBBLES THEREIN CASTING THE RESULTING AERATED SLURRY AGAINST A PATTERN, ALLOWING THE THUS CAST SLURRY TO SET, REMOVING IT FROM THE PATTERN, AND REMOVING THE WATER THEREFROM.

9. A MOLD FOR CASTING MOLTEN METAL, CONSISTING ESSENTIALLY OF A BODY CONTAINING A FILLER, AND SET CALCIUM SULFATE DIHYDRATE CRYSTALS THAT ARE IN TERLACED AND ACICULAR IN SHAPE AND WHICH BODY IS PROVIDED WITH INNUMERABLE INDIVIDUAL CONTIGUOUS VOIDS ARRANGED IN FOAM-LINE FORMATION, SAID VOIDS HAVING PERFORATED WALLS RENDERING SAID VOIDS INTERCOMMUNICATING, THER SURFACE OF SAID MOLD INTENDED FOR CONTACT WITH MOLTEN METAL BEING SMOOTH AND MERELY MICROPOROUS, AND THE PERMEABILITY OF SAID MOLD LYING WITHIN THE RANGE OF FROM ABOUT 0.7 TO 250 A.F.A. PERMEABILITY UNITS.