Milton Avery, Adolph Gottlieb, and Mark Rothko were pioneering figures in the American modern art movement. They were good friends, too. In 1932, the older Avery invited his two mentees to Cape Ann in Gloucester, Massachusetts, the beginning of shared sojourns to the coastal town. Avery was a stoic leader. He “never uttered a word of advice or instruction to any painter other than ‘do another one,’” the curator Eliza Rathbone has said. Far from the urban grit of New York, the men embraced the area’s secluded natural beauty and brought three singular forms of abstraction to their seaside paintings. This exhibition is the first to study the artists’ friendship in a coastal setting. Most of the 90 paintings and watercolors on view have never been shown before. —Maggie Turner