Andy Warhol

'At the office Sam tried to take pictures of me that I needed to work from for the Self Portraits for the English show, and I'd done my hair in curlers and everything and he just couldn't get it right...'

Andy Warhol Diaries

The mug shot, the mask, the void, the inscrutable nature of appearances and the relentless black humour of it all hit you the moment you enter the gallery. I think of Beckett '...the faces of the living, all grimace and flush, but can they be described as objects?' - but here the object is the life and death of Warhol himself, and the banality of his repetitions is absurd and compelling.

Since its heyday in 17th century Spain and Holland, the skull has functioned in painting as an obvious metaphor for the ubiquity of life and death, generically titled Vanitas. (In 17th century Spain, this type of painting was slightly less subtly known as Desegnano del Mundo - disillusionment of the world.) Here, 13 skulls are lined up, (Skull from 1976) isolated and painterly, without skin or brains, empty sexless and abandoned.

In these paintings, Death, the absolute, is paradoxically composed of variables. The skull is revealed to us through a moment of light (the photograph) and the death's head grins at us through a range of cheerful, highly-keyed colours. Warhol manipulated photographs until the line between painting and photography - what exists and what is invented - became blurred. Although each painting uses the same photograph of the same skull, the final image is made unique through the artist's manipulation of the surface. Small differences make the act of repetition more a renewal of the motif than a tautology.

In three small pictures from 1978, Self-Portrait with Skull, the skull perches like a crazy parrot on the shoulder of a creepy pop pirate. The self-portrait and the Vanitas have become one, and two sets of eyes (or sockets where eyes once were) stare at the viewer with a kind of deadpan humour. In 17th century painting, Christian admonition lay at the heart of the Vanitas. Here the skull exists free of confining righteousness, and the only hope of resurrection lies in the spectator's imagination. The Warhol dictum: to be looked at is to live.

In a more subdued triptych of the same year, Self-Portrait (triple image), three Warhol heads on three canvases blend to create a single image. It is a strangely melancholy overlapping, a trinity of self-obsession and doubt, where one head blurs into another and no single face dominates. By confusing the nature of the original (both of the self and the representation of the self) and then incessantly repeating it, Warhol reveals in these pictures a fractured self-image where unity only exists in multiplicity, and representation functions as an imperfect copy of an imperfect original.

In Self-Portrait Strangulation (1978), a suite of ten canvases, we interrupt a murder, and the artist gasps with a kind of cheesy ecstasy. His tie writhes and points to his throat. His eyes roll to heaven. The brutish hands around his neck aren't linked to a body, but death, the anonymous executioner, hovers like a thug.

In 1986, the year before he died, Warhol made a series of self-portraits commissioned by Anthony d'Offay. In this series, which includes Self-Portrait - Fright Wig (eight pictures, different colours, three sizes) and Self-Portrait, (seven pictures, different colours, three sizes), Warhol hovers in front of us again and again; implacable, disembodied and blank, with crazy hair and skin that caves and undulates over the structure of his own skull. However, for all their colour, size and high-key tonality, these are bleak images, like faces glimpsed in the hallucinogenic light of night-clubs - only just in control and slightly desperate. Warhol's severed head floats in the black void, like a spectral John the Baptist, moribund and sacrificial. In Self-Portrait with Camouflage (1986) Warhol's inscrutability is literally made flesh. He represents himself as both disguised and recognisable, abstracted and real. Once again, the self-portrait becomes an embodiment of the difficulties of self-revelation.

These paintings ask fundamental questions about picture-making - how can a complex personality be reduced to a single image? How to imagine the paradox of our own death, the impossibility of visualising our own mortality? The repetitious, mechanical nature of Warhol's process has always lent the eclecticism of his choice of subject (himself, skulls) an eerie homogeneity. Ideas are presented in pretty much the same way, but precisely what these ideas are is as elusive as the original in his multiples. In this show, the homogeneity has allowed the different genres to become interchangeable - the very existence of the still-life is contingent upon death's whim, and the anonymous skull in the Vanitas paintings is repeated like a mantra of Warholian wish fulfilment, a place where the complicated self is finally reduced to the purity of its mechanical structures. Like a machine, the skull without the body exists in a space where looks and personality cease to matter. Art imitates death.