: a white powdery slightly hydrated calcium sulfate CaSO4·1⁄2H2O or 2CaSO4·H2O that is made by calcining gypsum, forms a quick-setting paste with water, and is used in medicine chiefly in casts and for surgical bandages
plaster of paris
Quick-setting gypsum plaster consisting of a fine white powder, calcium sulfate hemihydrate, which hardens when moistened and allowed to dry. It is made by heating gypsum to 250–360°F (120–180°C). Used since ancient times, plaster of paris is so called because of its preparation from the abundant gypsum found in Paris. It is used to make molds and casts for ceramics and sculptures, to precast and hold ornamental plasterwork on ceilings and cornices, and for orthopedic bandages (casts). In medieval and Renaissance times, gesso (plaster of paris mixed with glue) was applied to wood panels, plaster, stone, or canvas to provide the ground for tempera and oil painting.