plaster of paris, quick- setting gypsum cataplasm conforming of a fine white greasepaint( calcium sulfate hemihydrate), which hardens when bedewed and allowed to dry. Known since ancient times, cataplasm of paris is so called because of its medication from the abundant gypsum set up near Paris. Cataplasm of paris doesn't generally shrink or crack when dry, making it an excellent medium for casting molds. It's generally used to precast and hold corridor of cosmetic plasterwork placed on ceilings and cornices. It's also used in drug to make cataplasm casts to incapacitate broken bones while they heal, however numerous ultramodern orthopedic casts are made of fibreglass or thermoplastics. Some sculptors work directly in cataplasm of paris, as the speed at which the cataplasm sets gives the work a sense of proximity and enables the sculptor to achieve the original idea snappily. In medieval and Renaissance times, gesso( generally made of cataplasm of paris mixed with cement) was applied to wood panels, cataplasm, gravestone, or oil to give the ground for aquarelle and oil painting oil. Cataplasm of paris is prepared by hotting calcium sulfate dihydrate, or gypsum, to 120 – 180 °C( 248 – 356 °F). With an cumulative to slacken the set, it's called wall, or hard wall, cataplasm, which can give unresistant fire protection for interior shells.