Robert Motherwell, Untitled (Ultramarine & Ochre Open), 1973, 69 x 44 inches, acrylic on canvas, Bernard Jacobson Gallery

I can't deny that Motherwell was a major figure in my early artschool days. Seeing one of his Elegies for the first time in 1971 at the Dallas Museum of Art was an important formative moment. Over time, those mid-career Motherwells haven't held up particularly well compared to the classic work of many of his contemporaries. But the Open Series was his late breakthrough -- unquestionably his most enduring contribution -- when he occasionally escaped his own mannerisms (if not Matisse's) to make tough and simple declarative paintings. Through August 28, the Bernard Jacobson Gallery in London is featuring a group of these works in conjunction with the publication of a book on the Open Series from 21 Publishing.