Since founding their firm in 1974, Billie Tsien (American, b. 1949) and Tod Williams (American, b. 1943) have deliberately maintained a small, focused practice, which permits them to concentrate on materials and the significance of craft in their work. At the distinctive American Folk Art Museum in New York, a singular gesture becomes the heart of an entire project: the bronze façade’s angled folds produce an entrance that literally envelops the visitor.