“I think van Gogh was one of the great, great draftsmen. I love the little sketches in his letters, which seem like drawings of drawings. They are condensed versions of the big pictures he was painting at the time, so that Theo and the other people he was writing to could understand what he was doing. These days he’d be sending them on his iPhone. When you look at them, they contain everything. It’s all there. He certainly didn’t do anything by halves.”