In 1941, at the age of seventy-one, Henri Matisse underwent radical surgery for abdominal cancer. The operation saved his life, but left him profoundly weakened and largely confined to a wheelchair or bed. To an outside observer, the legendary pioneer of Fauvism—the man who had spent four decades shocking and seducing the art world with uninhibited color—seemed poised at the close of his career. Matisse, however, viewed this precarious chapter not as an ending, but as what he called a seconde vie—a second life. Stripped of the physical stamina needed to stand before an easel for hours with a palette and brush, he simply invented a radical new visual medium:…