Christen Købke was the son of a master baker. He painted luminous skies and reddening sunsets.

But when he painted a street scene, you can peep through sparkling Danish windows to see geraniums in pots on the windowsill.

He didn't stray far from home and he painted people and places that he loved. (When he went to Italy, his paintings become much less interesting.) He painted his mother, who had 11 children. And he painted his friend, with whom he shared a studio. I'd like to think that had he born in this century, he'd have known how to upload pictures in the right order.

One of the portraits I loved best was done for the mother of a friend who was going abroad to study; she disapproved of her son smoking, and so Købke painted him chewing on a rose instead of his pipe. You can almost hear the two boys laughing at the joke of it and a mother laughing and crying at the same time.

As the National Gallery was closing, I stood for a moment looking at the rainy sky over Trafalgar Square. It was a Købke kind of evening.