Thornton Dial has never been one for talking much about his artwork. Ask him what inspires his monumental assemblages, made from twisted metal, tree branches, cloth, plastic toys, animal bones and all manner of found materials, and he is likely to respond tersely, as he did while showing me around his studio here one bone-chilling day last month. “I mostly pick up stuff,” he said. “I start on a picture when I get a whole lot of stuff together. And then I look at the piece and think about life.”