Plaster of paris

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plaster of paris, quick-setting gypsum plaster consisting of a fine, white powder, calcium sulfate hemihydrate (see calcium), which hardens when moistened and allowed to dry. Plaster of paris is prepared by heating calcium sulfate dihydrate, or gypsum, to 120°–180° C (248°–356° F). With an additive to retard the set, it is called wall, or hard-wall, plaster.

Used since ancient times, plaster of paris is so called because gypsum was early used near Paris to make plaster and cement. Plaster of paris is also used to precast and hold parts of ornamental plasterwork placed on ceilings and cornices and is used in medicine ... (100 of 171 words)