Doris Salcedo. Left: “Untitled,” 1998. Wood, concrete and metal, 74 x 44 x 21 1/2 inches. Collection of Albright-Knox Art Gallery, Buffalo. Photo: David Heald. Right: “Shibboleth,” detail, 2007. Installation at Turbine Hall; Tate Modern, London Concrete and metal, 548 feet long. Photo: Tate Photography, London. Courtesy of the Artist and Alexander & Bonin, New York.