A blockbuster exhibition, ‘Impressionism to Modernism: The Keithley Collection,’ goes on view starting Sunday, Sept. 11, at the Cleveland Museum of Art. Clevelanders Joseph and Nancy Keithley talked with The Landscape about their passion for collecting art and why they chose to make the largest gift to CMA in more than 60 years — 100-plus works ranging from paintings by Pablo Picasso, Henri Matisse and Andrew Wyeth to woodcuts by Chinese master Xu Bing.