The other side of US art revealed

Edward Hopper and Jackson Pollock are well known in Britain, but few will be aware of John Sloan, Louis Lozowick, Robert Gwathmey, Blanche Grambs or Charles Keller. This is hardly surprising, since they were socialists or communists.

Active in the first half the 20th century, they were duly dismissed as "un-American" during the cold war. Along with many others, including apolitical realists, they were overlooked or marginalised by mainstream art history, written at that time which trumpeted the "triumph" of US abstractionism.

With a few exceptions such as Hopper, this skewed narrative has lingered to this day, particularly in Europe.

But not any more. This marvellous exhibition introduces them and other little-known US artists to the British public.

At the beginning of the century, the Ash Can School rejected the idealisations and pretensions of academic art to engage directly with unvarnished life. It included the socialists John Sloan and George Bellows, both of whom made illustrations for the left-wing magazine The Masses.

An admirer of Hogarth, Sloan advised his students to leave the studio to go out into the streets and look at life. His etching Roofs, Summer Night (1906) does just that.

Slum dwellers have escaped the sweltering humidity of New York heat by sleeping on their tenement roofs. With swift accurate line, dramatised by sharp contrasts of dark and light, Sloan captures the unposed abandonment of real people asleep.

The next major section brings us to American modernism and precisionism, when cubism and expressionism were adapted to convey the speed, alienation, drama and dynamism of urban existence.

Now the city itself dominates. The country's skyscrapers are symbols of modernity. With his European background and contact with Soviet constructivists, Lozowick understood that this with an outsider's insight.

The abstracted geometric shapes and uncompromising harsh tonal contrasts of his lithograph New York (c-1925) suggests the electrifying disjunction of this city with the zest and zing of a Harlem dance band.

Meanwhile, artists such as Hopper and Martin Lewis continued to find drama in everyday city life without adopting modernist styles.

Influenced by the exaggerated lighting of film noir, Lewis's nocturnes evoke a tense ambience pregnant with possible narratives.

The 1929 Wall Street Crash changed everything. Artists suffered alongside their fellow beings. For example, Lewis, whose prints had been bestsellers, found his career collapsing with that of the art market.

As they experienced or witnessed the misery of rural and urban poverty, more artists became politicised. Gone were utopian visions of the machine age. More urgent was the need to raise consciousness by showing social injustice and exploitation.

Grambs's aquatint Miner's Head (1937) and Bernard Schardt's woodcut Woman in Kitchen (c-1938) typify the numerous sympathetic depictions of workers of this period.

From 1935, the Federal Art Project, part of the New Deal programme, provided a lifeline. Artists were paid a modest wage in exchange for works which were distributed to public institutions such as schools and court rooms.

The printmaking workshops of its graphics branch revitalised print making. For example, Gwathmey experimented with colour screen printing, a technique hitherto reserved for commercial printing.

Conducive to modernism's simplification of form and flat areas of unmodulated colour, this technique led to such powerful images as his Share Croppers (1944), portraying the harsh working conditions of rural African-Americans.

The rise of European fascism in the 1930s further polarised artists. Regionalists such as Thomas Hart Benton argued for political and aesthetic isolationism - modernism was an alien European import which tainted the US realist tradition. They created idealised images of US rural life.

The left agitated for political internationalism but was divided on the issue of modernism. The activist Stuart Davis defended the creative freedom brought by modernism, while others argued for the accessibility of socially engaged realism.

The communist Jacob Kainen recalled: "The depression had driven us to think of social change. In such an atmosphere, a more than passing concern with aesthetics was tantamount to frivolity."

Keller's People's Meeting (1943) imparts the intelligent concentration of an audience at a public meeting with a directness which avoids overt distortion. Others, such as Jolan Gross Bettelheim, equally committed to communism, produced prints such as Home Front (1943), which communicates the efficiency and bustle of wartime factory work by using futurist repetition and simplification. Both artists suffered in the McCarthy era.

This fair-minded exhibition is curated with subtlety. Its learned scholarship is worn lightly but informs a judicious selection from the British Museum's large collection. Informative without being overly didactic, it covers much ground without being overwhelming.

If you cannot get to the London exhibition, look out for it next year when it travels to public museums in Nottingham, Brighton and Manchester.

It is a must for socialists. These humanist prints will restore your faith in human endeavour.

This exhibition is free and shows until September 7.