The choice of material directly impacts the mold's lifespan and the quality of the final ceramic piece. Plaster of Paris (Gypsum) is the industry standard for slip casting due to its excellent water absorption properties, which allow the clay to form a skin quickly. For high-volume production, look for Alpha Gypsum, which offers higher density and superior compressive strength. If you are performing press molding or using RAM presses, ensure the molds are made from porous resin or high-strength synthetic materials that can withstand mechanical pressure without cracking.