A mixture of lime, sand and water. When used for sculpture, plaster can be used to make mould-making and casts or initial small-scale or full-scale models. Plaster of Paris (also called gesso) is made by heating gypsum and then crushing it to a fine powder, which when mixed with water, sets to a hard brittle solid. It is relatively cheap, fine-textured, easily mixed and quick-setting. Ideal mould-making material, it flows easily into gaps and during the process of drying expands slightly, forcing the plaster into the finer details of the mould.

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John Colet
after Pietro Torrigiano
circa 1518
NPG 4823

Mary, Queen of Scots
after Cornelius and William Cure
1870, based on a work of 1606-1616
NPG 307a

John Milton
by Horace Montford, after a bust attributed to Edward Pearce
circa 1860-1919, based on a work of circa 1660
NPG 1396

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