There are some benefits to the credit crunch. One of them is that I recently picked up a handy little book called Frames, written by the (now) Director of the National Gallery, Nicholas Penny. The original price was not much more than £3, and I could probably have risen to it, but the obligatory time-of-crisis reduction made it irresistible.

Dr Penny reveals frames to be the equivalent of the well-tailored suit: an exquisite yet unobtrusive complement to what’s inside. There are frames to Gothic altarpieces, with delicately carved tops and, if you don’t mind kneeling to see them, star-spangled vaults. Flemish artists worked on panels that were already framed, in whole or in part.

As the concept of the picture gallery hadn’t yet emerged, these intimate paintings were probably stored in chests, rather than hung permanently on walls, the owner taking them out to enjoy as a treat. By the time of the Impressionists, historic frames had assumed a value of their own, Renoir’s chubby nude of A Bather being set off by a frame from the age of Boucher. Outside the National Gallery, Antony Gormley is organising an artwork on the empty plinth in Trafalgar Square: hundreds of ordinary people will stand there for an hour each. Now there’s a framing challenge.