No big museum or art gallery can ever stand still. Like the national economy, it has to grow. Even if the collection is relatively static, a steady state of being is not enough. Such places become over-familiar, start to look tired, fail to cater to the needs and desires of a public that is increasingly spoiled for choice. And so the National Gallery, 13 years since it opened its capacious and capricious post-modern Sainsbury Wing, is at it again. Now, you can walk into another, £21m, new wing. This one, though, is entirely invisible from outside. It is an architectural conjuring trick. The team that has done this is exactly the same team that produced, as if from nowhere, the much-praised Ondaatje Wing of next door's National Portrait Gallery a few years back. Same client: the National Gallery's director Charles Saumarez Smith used to be at the NPG. Same architects: Sir Jeremy Dixon and Edward Jones are the wand-wavers. And the job has been done in pretty much the same way, by revealing and roofing-over a forgotten internal lightwell. Only the private sponsors are different: instead of an Ondaatje Wing, we have the Sir Paul Getty Entrance and the Walter and Leonore Annenberg Court.
The philanthropic financing of new cultural courtyards - think also of the British Museum, National Maritime Museum and Wallace Collection - is no bad thing to do. Do not be put off by the fact that all these projects are more about making profitable public space than they are about extending gallery space. That trail was blazed back in 1988 by the Victoria and Albert Museum's much-maligned but wholly memorable advertising campaign "an ace caff with quite a nice museum attached". It was scoffed at then, but today we know that this is by no means a cynical exercise: it is absolutely necessary.
