A dry white powder base made of sand and limestone mixed with water. Depending on the consistency, plaster can be spread on a flat surface such as walls in building construction or modeled by sculptors into finished works or used for molds for clay or terra-cotta finished figures. When dry, plaster can be quite hard and durable. American sculptors who have used plaster as a finished product include Claes Oldenburg whose first pop-art figures in the 1970s included a mock store filled with plaster objects; George Segal, whose signature works were life-size human figures of upainted plaster; Manuel Neri, whose earliest pieces were in plaster; Peter Agostini who did plaster forms over various armatures that anticipated Pop Art; and Deborah Butterfield whose first life-size mares, done in the 1970s, were painted plaster over steel armatures. (They proved so heavy she changed to lighter assemblage materials). Sources: Kimberly Reynolds, "Illustrated Dictionary of Art Terms". "Phaidon Dictionary of Twentieth-Century Art"; AskART biographies.