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With judicious heating, gypsum converts to the partially dehydrated mineral called bassanite or plaster of Paris. This material has the formula CaSO 4 ·(nH 2 O), where 0.5 ≤ n ≤ 0.8. [8] Temperatures between 100 and 150 °C (212–302 °F) are required to drive off the water within its structure.
Gypsum plaster, [12] also known as plaster of Paris, [13] is a white powder consisting of calcium sulfate hemihydrate. The natural form of the compound is the mineral bassanite . [ 14 ] [ 15 ]
The word gypsum is derived from the Greek word γύψος (gypsos), "plaster". [9] Because the quarries of the Montmartre district of Paris have long furnished burnt gypsum (calcined gypsum) used for various purposes, this dehydrated gypsum became known as plaster of Paris. Upon adding water, after a few dozen minutes, plaster of Paris becomes ...
The plaster is not pure plaster of Paris, but rather has additives to improve green strength, dry strength, permeability, and castability.For instance, talc or magnesium oxide are added to prevent cracking and reduce setting time; lime and cement limit expansion during baking; glass fibers increase strength; sand can be used as a filler. [1]
A common casting medium, plaster is also a popular pick for making molds. Using this substance, which is manufactured in powder form, is ideal when you want a rigid structure to make casts as an ...
Gypsum mortar, also called plaster of Paris, was used in the construction of many ancient structures. It is made from gypsum, which requires a lower firing temperature. It is therefore easier to make than lime mortar and sets up much faster, which may be a reason it was used as the typical mortar in ancient, brick arch and vault construction.
A restored gesso panel representing St. Martin of Tours, from St. Michael and All Angels Church, Lyndhurst, Hampshire. Gesso (Italian pronunciation:; 'chalk', from the Latin: gypsum, from Greek: γύψος), also known as "glue gesso" or "Italian gesso", [1] is a white paint mixture used to coat rigid surfaces such as wooden painting panels or masonite as a permanent absorbent primer substrate ...
One design has a thin layer of hardened plaster of Paris on the bottom to absorb the killing agent. The killing agent will then slowly evaporate, allowing the jar to be used many times before it needs to be refreshed. The absorbent plaster of Paris layer also helps prevent the agent sticking to and damaging insects.