In Velásquez's `Bufon' in the Prado, the man's right hand in a sweeping gesture points to an absence of background while his left hand clutches at his coat as if grasping at himself. The coat is black and it has a marvellously painted edge. But the hand looks so much more real than what it is grasping, as if it is clutching at nothing, as if what it holds is no more than this `absent' background. Of course this is only a piece of painted cloth - but there he is on the wall of the gallery outlasting the `real' him by hundreds of years. Is this what the clown is telling us? He comes up at you out of this absence, arriving with a rhetorical flourish and on his face an expression of settled melancholy as he clings to himself while flinging out his other arm.

`View of the Westerkerk, Amsterdam' by Jan van der Heyden, in the National Gallery, is a townscape, the picture crossed by a canal. But the figures strolling by the canal were added later `by another hand', and consequently, unlike the trees, are not reflected in the water and cast no shadows. In the room where it hangs there is a silent, shuffling procession, people passing through to see the Masaccio Altarpiece briefly on show in the next room. It's as if, encountering the painting's silence, we are those shadowless figures.

`Wordsworth's Cupboard', a painting by the artist Jeff ...