Uncoated plaster surfaces are easily stained by liquid and it’s not very strong – which means for large works, artists usually want to layer plaster over wood or paper or straw, to reinforce them. The drawbacks to using plaster made this way? “It shrinks a bit as it cools, meaning that there is a risk of bubbles and surface imperfections. An exothermic chemical reaction then occurs, which means that as you mix it, it gets hot, hot enough to burn skin, and then hardens quickly.” You heat gypsum until it becomes a powder, and mix that powder with water. Although many varieties of plaster exist, the basic recipe for artists – what we call plaster of Paris, after the large gypsum deposits outside Montmarte – is relatively simple. Which is funny because water is a main ingredient. “Its only enemy,” says Lisa Ellis, AGO Conservator, Sculpture and Decorative Arts, “is humidity. It makes detailed impressions and, when protected, is very durable. Molded when wet and carved when dry, plaster can be used for sculpting, wall coverings and ceilings. Used by everyone from ancient Egyptians to the avant-garde to create replicas and original artworks, plaster is as enduring and brittle as memory itself. A hockey player two metres tall, a wall of footprints and a shelf of future fossils – the AGO is home to a world-class selection of plaster artworks.
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