Plaster of Paris is one of three types of plaster. The other two are lime plaster, made from calcium hydroxide and sand, and cement plaster, a combination of plaster, sand, Portland cement and water. Plaster of Paris is the most commonly used plaster and is also called gypsum plaster.
Plaster of Paris, or gypsum plaster, is made by heating gypsum to 150 degrees centigrade, and then mixing the dry plaster powder with water. The powdered gypsum is mixed about two parts plaster to one part water, to create a paste.
Paris was known as the "capital of plaster" in the 1700s because plaster was widely used to coat the wooden walls of houses. This helped protect against fire. Gypsum plaster became known as "plaster of Paris."
Plaster of Paris, when mixed into a paste, hardens into a smooth solid with a soft and malleable surface. Plaster of Paris hardens quickly, before the water in it evaporates, so it does not shrink as it dries. Tools and sandpaper can be used to sculpt or carve dry plaster of Paris.
Plaster of Paris, which is one type of plaster, is used in construction as a finishing materials, and in the arts, especially for sculpting. It can be cast, modeled or carved.
Dry plaster, including plaster of Paris, can be painted or sealed with wax, oil or shellac. Pigment and textural agents, like shells and small stones, can be added to plaster of Paris when mixing.
When sanding or carving plaster of Paris, it is important to wear a respirator or dust mask, as gypsum powder can cause respiratory distress.