Mill material is a term used to refer to the materials used in the production of goods. GRIST, IRON, STEEL, and pigiron are all examples of mill material. GRIST is a type of grain that is ground into flour or meal. IRON is a chemical element that is used to make STEEL. STEEL is an alloy of IRON and other elements, such as carbon, that is used in construction and manufacturing. Pigiron is a type of IRON that is produced in a blast furnace and is used to make cast IRON and STEEL.