Great works: Sand dune (1983), Francis Bacon

W H Auden's lines make a clear announcement. "To me Art's subject is the human clay/ And landscape but a background to a torso". It's a manifesto. Humanity, he wants to say, is the primary thing in Art. Everything else takes second place. Or so it seems.

But the words he chooses are not so sure. The human clay? They could let our imaginations run, taking us into stranger regions of flesh and matter and flux. Auden envisages a little moulding, a little baking, producing a safe and separate figure, and that's all.

Clay, though, is a very malleable and transformative medium. It is wet. It squashes. It has no limits. It comes from the earth and can be pressed back into the earth. And so the distinction that Auden strictly draws between a torso and a landscape is only relative. Body and ground can easily merge.

Look at paintings. Landscapes and nudes often lie down together. The rolling hills and the curving limbs can join in harmony, or fuse into something even closer. There is view of a coast by Degas, for example, where the shapes of the grassy terrain are also clearly the emerging forms of a naked woman on her back. And this Degas is probably an inspiration to a painting made almost a century later. Here the medium is a different stuff: human sand.

Francis Bacon's Sand Dune isn't exactly landscape. It is a heap and a slide of sand, an extract of the outside, perhaps from the seaside, perhaps from a builder's site, but now it's been taken inside, and put on stage. The scene has various stagey devices often used by the artist: a glass chamber, a hanging light bulb, a pointing arrow, a disc of blue spotlight on the floor, a dark suggestion of a shadow or a leak.

On this stage, the volume of sand has a weird physical presence. It is partly contained within the tank, and partly spilling out and through the sides of the tank, and most of it seems to be viewed as if in a 3D magnifying case, so when it appears outside (at the right) it visually shrinks. The bright blue screen at the back is sky, another extract of outdoors, or a screen projection.

But the sand dune itself is obviously the protagonist. You could call it a thing. You could call it stuff. It's certainly the subject. And unlike many of Bacon's subjects, bodies or heads, this one retains its integrity. Its form is not radically distorted or disrupted or dematerialised. This dune is a solid, continuous mass.

It is sand; but of course not only sand. It is also flesh, a pure flesh. This flesh has no rigidity, no internal structure, no tension, no action. It is simply a contour of skin, containing soft blob. It lies, lolls in itself, it has sinkings and swellings, it rolls in indolence, melding into a single flow. It might be the fattest person in the world, who has lost all parts.

Or rather, not quite. It is like pure flesh but it also has hints of a creature within it too. An anatomy exists, just about. There are buttocks rising, a bending left knee sticks out at the front, a right thigh is stretched out, even a shoulder and an elbow become visible. As you look more closely, this figure appears, face down, stirring like mounds from the sand, like somebody covered in sand, or made loosely from sand.

Ambiguities arise. This mass is uncertain between anatomy and sheer flesh, uncertain between flesh and various other substances, which could be powder or liquid or pulp. Sand itself is well-chosen and imagined. It's an intermediate stuff that can be dry and pulverised, or a running, pourable fluid, or a quite compacted, malleable paste, like clay.

Sand Dune is in metamorphosis, in a calm hysteria. It's an entity that can come half alive, and enjoy feelings. It can be picked up by the shovelful. It can be stroked and smoothed. It can cascade. It can be dispersed and lose all sense of limits. At different points around the dune, these different sensations come to the fore. There are even moments when it seems like dust in air.

And then at the crest of the dune there is something like a tuft of rough grass, or a crop of hair. It comes to the vestigial beginning of a head – a final intimation of the human about to break the surface.

About the artist

Francis Bacon (1909-92) used to be a nightmare visionary. His Screaming Popes and Crucifixions were horror shows. But this Soho bohemian was also a performer. His colours are gorgeous. His paintings look less blood-curdling – and more sumptuous, energetic, graceful, playful, even jolly.