Plaster mould casting is a metalworking process that uses plaster of paris moulds instead of sand. The plaster is mixed with additives to improve its strength and permeability. The process involves spraying a pattern with parting compound, pouring plaster around it, baking the mould to remove water, and then pouring molten metal into the mould cavity. It produces parts with good surface finish and accuracy, and can be used to cast small and complex non-ferrous metal parts.