Also known as Plaster-of-Paris, gypsum plaster is a building material that features similar properties to mortar or cement. It is created by heating gypsum, a soft, naturally-occurring mineral, to roughly 300 degrees Fahrenheit (150 °C), and then mixing it with water. The resulting paste hardens as it cools, forming a relatively soft, pliable finished product. Unlike mortar or cement, which dry much harder, gypsum plaster can be sanded or otherwise manipulated once cured, making it a good option for aesthetic, non-load bearing purposes.
Gypsum plaster derives its other name, Plaster-of-Paris, from the discovery of a large cache of gypsum in Paris, and its resulting proliferation as a building material in the city throughout the 1700s. Though its use can be traced back much farther — with samples dating from as far back as 7,000 BC in Mesopotamia — it gained widespread popularity throughout Europe after the Great Fire of London in 1666. During that fire, the city was nearly completely destroyed because flames spread through the close-packed arrangement of wooden buildings. Its utility as a fireproof material remains strong today.
Gypsum plaster is renowned for its use as an art medium, specifically for frescoes. Much of the reason that many Renaissance-period Italian frescoes remain intact and vibrant is due to the permeability of the plaster. This allowed inks to sink beyond the surface, much like the ink in a tattoo. This type of plaster is also a popular material in making casts for stone or metal sculptures, as it can be finely worked. Plaster can be used as a sculpture material itself when dried over a metal frame, though it is not particularly durable in this form.
In modern use, gypsum plaster is common in a number of industries. Orthopedic casts that incorporate plaster-soaked pieces of cloth remain a vital tool in the medical field to support and protect broken bones. In dentistry as well, plaster is used to create models of oral features for dental work. Gypsum plaster is still featured in architecture, particularly aesthetic pieces, and is used extensively in specialty industries, including film and theatre, where it can simulate materials such as bark or stone.
While a common and ancient material, gypsum plaster is not totally inert and can pose a health risk if used incorrectly. Improper use can result in severe burns, as the reaction between plaster and water releases potentially dangerous amounts of heat. Additionally, some types of plaster, particularly in older settings, can include particles of asbestos, a known carcinogen.