The veteran American artist Alex Katz was inspecting the hang of his new paintings while I looked at them, but I could not ask him any questions. I was dumbstruck. The only thing I could have said to him at that moment would have been a stuttered, “How come you paint so well?”

How can simple pictures of faces be so unexpected, exciting and fascinating? Katz has been painting portraits for a long time now – he’s 87 and began his career in the age of Jackson Pollock – and his latest works do not shatter his established style. Their main novelty is that all the figures are set against black. Many of the pictures have a wide CinemaScope format so the people in them stand out as colourful shapes against a nightscape of glossy darkness.