H ere is something to try next time you go into an art museum. Go to the Old

Master galleries but don’t look at the paintings in the ordinary way. Stoop

down so you catch the glare of the lights, and look up at the pictures. You will

not be able to see what the paintings show, but you’ll get a good look at the craque-

lure: the fine network of cracks that scores the surface of most Old Master paintings.