The Critics: Exhibitions: Rembrandt's poodle

Rembrandt by Himself National Gallery, London

'Once in a lifetime," whispers Rembrandt in the slogan on the London Underground posters for "Rembrandt by Himself". It's that simple, but it's also one of the understatements of the century. No one has ever been able to enjoy an exhibition devoted entirely to Rembrandt's self- portraits before. "Once in this millennium" would be more apt.

Rembrandt's self-portraits are part of the mythology of western culture. They provide the classic image of the modern artist: alone, introspective, bankrupt, misunderstood, tormented by creditors and by his own sense of mortality, staring into posterity for reassurance of future fame. So at least the portraits seemed in Sir Kenneth Clarke's television sequel to Civilisation, back in the mid-1970s. Quite how much Clarke could read into each of Rembrandt's wrinkled eyebrows never ceased to amaze, programme after programme. But one could not help wondering how much was the fruit of his romantic imagination, rather than of his acute sensitivity as a former director of the National Gallery.

Now, a generation later, we have a fresh perception of Rembrandt. Through about 60 images, the National Gallery's exhibition sets out the many different motives that prompted his portraits. We find Rembrandt simply using his reflection as a model, in order to build up a reference collection of expressions for cameo roles in his biblical and historical scenes. He paints experimental character heads in costume in which the artist's likeness was not the priority, and he supplies portraits to satisfy his own growing celebrity market. By the time he was 27, Rembrandt was sufficiently famous to have a self-portrait in the Royal Collection of Charles I, and his assistants were copying others to sell, complete with the addition of his autograph. No wonder the Rembrandt industry has long continued to flourish, with the Rembrandt Research Project, founded in 1968, still sifting the evidence.

Of the 1,000 paintings considered genuine at the start of this century there now remain about 250. The exhibition offers ample opportunities for connoisseurs to test their skills: borderline candidates aspire for reinstatement, and there's the reassuring appearance of a completely new discovery, lent from a private collection. Beyond the supporting evidence of X-rays we now have proof of paintings as being from the very same plank of wood or roll of canvas when weighing them against works of more secure authenticity.

The variety of motivations and hands at work is, however, of secondary interest when one passes, disturbingly, through room after room of the same set of staring, hooded eyes. The spectacle of Rembrandt's face in gentle decay, from his early twenties to his sixties, is sobering, particularly given the artist's clinical accuracy in recording his sinking jaw- line and reddening eyes.

Only that nose, that gloriously bulbous, outrageous stonker of a nose, remains unchanged, try as he might to ennoble it through shadows and more flattering angles before, eventually, giving up. Rather like entering a large family reunion for a wedding or funeral, one at first is amused by the close resemblances, the common likenesses, until one realises how rapidly friends have aged, almost beyond recognition.

The younger Rembrandt was clearly a bundle of fun, if occasionally pretentious in his feigned gentility. The only full-length of him shows the artist dressed up like a tubby magi at a Christmas nativity play, wrapped in a turban, old dressing gown and recycled curtains. Painting his own feet proved too much for him. He never tried it again, preferring to conceal them behind an endearingly sullen poodle (as is revealed by comparison with an early copy by one of his assistants). Elsewhere, the artist appears more like a prop forward from the third XV.

But a darker side emerges in middle age: a confrontational, almost thuggish bully, standing in the shadows, ready to take on his critics.

The best exhibitions make us see the most familiar images completely afresh, and here it is: the turn of the Portrait of the Artist from the Iveagh Bequest at Kenwood House, London. Two years ago, when the Independent on Sunday published a survey of Britain's favourite 100 paintings, this magnum opus autobiography in paint was the cover story. To see it hanging as the centrepiece of the exhibition is to encounter it as if for the first time. Like so many brothers and distant cousins, the other paintings from the last decade of his life seem to shuffle aside, for he is the star, briefly back from Hollywood, not caught like that chance first glance in the bathroom mirror the morning after, not puzzling through a burning stare from the brink, not waiting patiently for the kettle to boil, but standing, hand on hip, holding court, ready to face his audience. He is the man; ecce homo. The famous circles in the background, Rembrandt's cryptic challenge to future scholars, amplify and open outward his stance, embracing the gallery to left and right. If ever a male portrait has mesmerised crowds of visitors, combining the fame and frisson of Mona Lisa, this is it. Whether we are witnessing a search for self or celebrity in these portraits, clearly it was not all done with mirrors.

The organisation of the exhibition (sponsored by Thames and Hudson) is almost as miraculous. Clearly, we live in an age in which no subject seems impossible; when fantasy exhibitions of which scholars once only dreamt can now be realised, thanks to the latest standards of conservation and international transport. A blockbuster no longer needs to be vast and all-encompassing to draw the necessary paying crowds if the subject is right.

We may not admit to any outbreak of millennium fever as yet. But once-in-a-lifetime shows like this are symptoms of an age of ambition and reflection, a sentiment which Rembrandt would have understood entirely.

National Gallery, WC2 (0171 0171 747 2885) to 5 September

Julius Bryant is Director of Museums and Collections at English Heritage