Mirror image

In one of Jorge Luis Borges' enigmatic stories, the Heresiarchs of Uqbar declared mirrors and copulation to be abominable because they increase the numbers of men. Dr Jonathan Miller's exhibition at the National Gallery shows that, at least as far as mirrors are concerned, artists take a different view. Since the 15th century, painters have included reflections in mirrors, water, and other shiny surfaces in their work. Apart from providing a way to represent textures and shapes with greater verisimilitude, reflections let them escape some of …