Jackson Pollock. Summertime: Number 9A.

Five and a half metres, one rhythm

Summertime: Number 9A was painted in 1948. Its size is the first thing a viewer notices: under a metre high, yet about five and a half metres long. The eye cannot take it in at once. You have to walk along it, as along a wall or a shoreline.

On raw canvas, black lines loop, break and loop again. Between them fall small, brighter patches of colour. There is no centre. No part matters more than another. It reads like music written horizontally, each passage with a new beat but the same song.

The materials are not purely those of painting either. Tate lists oil paint, enamel and ordinary commercial house paint. Each flows, dries and shines differently. Up close the surface is flat in places, ridged in others, glossy in others still.

A canvas on the floor

In 1945 Pollock left New York for Long Island. He and his wife, the painter Lee Krasner, lived in Springs, East Hampton. Their house and studio are now a National Historic Landmark open to visitors.

His studio was a converted barn with no heating and no lighting. He worked by daylight, and he laid the canvas flat on the floor instead of standing it on an easel.

It sounds like a small change, but it changed everything. With the canvas on the ground he could walk around it, stand at its edge, lean in from any side. Paint was no longer brushed from the wrist but dripped, poured and flicked with the whole arm and body. The picture records not only colour but the path of a body.

Tate notes that Pollock wanted to work directly from the unconscious. He once said the modern artist expresses an inner world: energy, motion, unseen forces. Summertime shows this clearly. Its rhythm is the rhythm of a man moving around a canvas on a summer day.

Beneath the web

At a glance, Summertime is wholly abstract. Yet several commentators have suggested that a frieze of figures lies beneath the web of paint, like an ancient band of standing forms. Some of the heavier black marks may be what remains of them.

No one is certain. But the idea adds a layer. Perhaps Pollock began with figures, then wore them away with his own movement. What survives is not the figure but its rhythm.

It may also explain the length. A procession needs width. Walking along the canvas, the viewer retraces the path of shapes that have disappeared.

A painting to walk beside

Tate bought Summertime: Number 9A in 1988. It usually hangs on a long wall, and viewers almost always do the same thing: walk slowly from one end to the other.

Pollock's work is often called action painting, a name that points to the painter. But before Summertime the viewer has to act too: walk, stop, step back, step in. The picture refuses a single point of view.

Perhaps that is why the title fits. Summer is not a moment but a stretch of time, long, rhythmic, then gone. Beside the quiet fields of Rothko, of the same generation, Summertime has almost nowhere to rest. It only has a path, and the viewer is invited to follow.