BENTONVILLE, ARK.- A luminous 19th-century landscape and a contemporary tapestry that confronts viewers with Civil War-era racial violence, both by important African American artists, are the latest works announced by Crystal Bridges Museum of American Art. Flatboat Men (1865) by Robert Scott Duncanson builds on the collection’s strength in Hudson River School paintings, joining works by Jasper Cropsey, Thomas Moran and Asher Durand. Duncanson is thought to be the first black artist in the United States to make a living as a painter and become internationally known. A Warm Summer Evening in 1863 (2008) by Kara Walker supplements other post-modern works in the museum’s collection that use unconventional media to rethink the past. Walker is widely acclaimed for exploring the intersection of race, sexuality and violence through the traditionally proper Victorian medium of cut-paper silhouettes. Shimmering sky and w