Since the 1950s Chicago’s Union League Club has hosted numerous exhibits emerging artists; this week it turns to Chicago’s old masters. The 18 artists featured in the club’s first invitational show include Roger Brown, Jim Nutt, Paul LaMantia, Ruth Duckworth, Don Baum, and Margaret Wharton. The show, at Prince Gallery, 357 W. Erie, opens tonight with a reception from 6 to 9 and continues through October 29. Gallery hours are 10:30 to 5:30 Monday through Saturday; admission is free. Call 266-9663 for more.