Cézanne's Card Players, Courtauld Gallery, London

This faultless gathering-in of paintings and drawings on a single theme marks a high point in the career of Paul Cézanne

Frenchness apart, you'd think that Yves Klein and St Martin of Tours would have nothing in common, and you'd be wrong.

There's the colour blue. St Martin, a fourth-century bishop, tore his blue cloak in two and gave half to a pauper. That bit of cloth, "the first flag of France", is memorialised in the blue of the Republic's tricolour. Sixteen hundred years later, the madcap Klein scandalised Paris by mixing chalk with ultramarine paint and dubbing it International Klein Blue (IKB).

The French have always had a bolshie streak, and blue has been its colour. So blue is a good place to start when looking at Cézanne's Card Players at the Courtauld Gallery, the works in the show being variously revolutionary. I am of the firm belief that the Courtauld's exhibitions can do no wrong, and this one proves the point. To the gallery's own version of The Card Players are added two of the four others that Cézanne made of the subject, one from the Metropolitan Museum in New York and another from the Musée d'Orsay. Alongside these are individual paintings of the men – sometimes two, sometimes four – who sit or stand around the table of the finished pictures, and next to these again, drawings and studies in pencil, watercolour and oil.

If you're a Cézanne-ist, two elements of this description will have piqued your interest. First, there is the fact that the artist worked up his subject through several stages from sketch pad to multi-figure canvas, a relatively unusual thing in his practice. Untypical, too, is the number of variants Cézanne made of The Card Players. Along with his baigneuses and views of Mont Sainte-Victoire, the five card pictures and their attendant studies and sub-parts form one of the most coherent parts of his oeuvre. If Cézanne's bathers set out to modernise the nude and the Mont Sainte-Victoire works to update landscape, then The Card Players take on the traditions of Dutch genre painting, those scenes of pub life and peasant revel beloved of Jan Steen.

But Cézanne's card players are not red-faced Haarlem sots. Far from it, they are sober, grave, maybe a little dour; in their big hands and weary postures, you see hard work in fields. Nor are the joueurs de cartes other than distantly related to the Paris bar flies of Degas and Manet. In overturning the historical assumptions of genre painting, Cézanne is telling us a pointedly different truth from theirs, a story of strength and solidity. The impassivity of the card players makes them as timeless as the mountains around Aix, and as monumental.

So it is apt that they should have a sculptural feel, as they do. In the Metropolitan Museum's The Card Players, dating from 1890-92, the figure to the right wears a smock whose incised folds Cézanne treats as stone. They might easily be marble-white, although they are actually blue – or rather bleu, French overalls being known generically as bleu de travail. The model for the figure is probably one of the workers from the Cézanne family estate, Jas de Bouffan. The room in which he and his fellow players sit is the studio in the artist's house.

And so, on various levels, what we see in this picture is the breaking down of barriers, a kind of democracy. Whatever the truth of the situation, the feel is not of a landlord ordering his peasantry to pose. Rather, the composition of this early picture places Cézanne in the position of a fourth card-player, or at least of a second onlooker. The intentness with which the men stare at their cards is the same with which the artist stares at them. Despite the sketches and studies, The Card Players' straight-on to-the-canvas, premier coup brushwork has the air of informality, of a solidarity between manual workers. There is no obvious picture plane, no varnished surface to separate us (or Cézanne) from them and suggest a barrier. Artist's smock and peasant's smock are one.

All this suggests that the The Card Players have a political agenda, although I doubt this is so. Rather, the social freedom and openness of the pictures allow Cézanne to be open and free as an artist. The Courtauld's own version of the subject, made four years after the Met's, has a denser, more tilted composition, one that hints at the fractured planes of Cézanne's revolutionary last period. By now, the bleu de travail of the earlier picture has dissipated throughout the canvas, so that colour and form are part of a single experiment. It is an extraordinary moment in Cézanne's career, and, as ever at the Courtauld, this show does it full justice.

Courtauld Gallery, London WC2 (020-7848 2526) to Jan 2011

Next Week:

Charles Darwent sees Fiona Banner at the Frith Street Gallery