EXHIBITIONS / The naked face: Pressing a face to the window of history: Andrew Graham-Dixon on Hans Holbein's portraits of the court of Henry VIII, at the NPG

Hans Holbein the Younger drew Sir Thomas Elyot one day in 1532. The sitter gazed off to the artist's left, made sure he kept still and staved off boredom with a daydream. Four and a half centuries later, Elyot survives death in Holbein's disconcertingly vivid image of him. He is faintly flushed, his cheeks dark with stubble and his greenish blue eyes thoughtful. His face is precisely observed, down to immature sideburns and a few strands of hair that have truantly separated themselves from the lank combed mass of the rest. Holbein's Tudor knight is almost palpable but he remains inscrutable.

Elyot, a man of destiny with a five o'clock shadow, may be contemplating his recent and momentous impact on the course of English history. When Holbein drew him he was recently back from Spain, where he had been engaged in an abortive act of diplomacy, attempting to enlist Charles V's support for Henry VIII's divorce from Catherine of Aragon. Henry's ensuing break from Rome, the dissolution of the monasteries and the iconoclastic ransacking of church and cathedral - here is a man at the epicentre of one of the most profound upheavals in the history of this nation, one that would alter its cultural landscape forever. Elyot may be reflecting on all this. Or he may just be thinking about his lunch.

Holbein's drawings of the court of Henry VIII, temporarily on loan from the Royal Collection to the National Portrait Gallery, are both extraordinary and tantalising in their immediacy. To inspect them close to, as the dim lighting of the exhibition and the quiet virtuosity of Holbein's realism demands, is to press your face up to the window of history. The experience is fascinating but frustrating because the glass, while clear, is soundproof. These people are tremblingly alive but also remote. They think, but not out loud.

Holbein's portrait drawings are small miracles, still images snipped out and preserved from the lost film of the past. What we know about the people he perpetuated is likely to colour our response to these likenesses. It is tempting to discern, in his portrait of the ill- fated poet Henry Howard, Earl of Surrey, with his long oval face and dreamy eyes, an unworldly and somewhat vulnerable character; and equally tempting to read into the face of Surrey's childhood friend and eventual betrayer, Thomas Cromwell's henchman Sir Richard Southwell - with his cold eyes and grim, set mouth - a look of calculation and callousness. But hindsight should not lead us to credit Holbein with too much insight. The artist seems too neutral for that and the face is by no means always a reliable guide to the soul. Holbein's most saintly subject of all, Sir Thomas More, might easily be taken, at face value, for a thug.

The relative informality of Holbein's drawings enhances their ambiguity: these are people observed rather than people aggrandised, people intensely scrutinised but not accompanied, as they would be in the artist's finished oil paintings, with symbolic attributes of chastity or power, dynastic continuity or moral and spiritual probity. This makes them both more and less informative than some of Holbein's more elaborate portraits in oil: more informative in that they show us people as they physically were, and less informative in that they reveal little of how they wanted to be seen.

One drawing in this show, the highly finished study of the now destroyed Whitehall mural which the artist painted for Henry VIII, may help to measure the difference between the formal and the informal Holbein. This is not a preparatory sketch but, rather, the cartoon for a state portrait. The king stands before us, legs straddled, one hand on his hip, the other on the dagger at his waist. He is broader than he is tall: a man transformed into a superman or a kind of God on earth, strong enough to shoulder the weight of his dynastic responsibilities and to bear the burden of shaping his country's future.

It would not be long before Henry would be unable to bear even the burden of his own weight and have to be carted around his various palaces in a contraption on wheels. But Holbein the court propagandist could transform deformities into strengths: Henry's vast bulk has been remade into an image of redoubtable, formidable solidarity, sheer weight made to convey, instead, weightiness. While the image might not bear nearly such a close physical resemblance to Henry VIII as Holbein's portrait drawing of Sir Thomas Elyot once did to its subject, it may tell us more about him in another way. The Whitehall mural sketch is the image not of a man but of his qualities: a picture of frightening ruthlessness, of naked power and ambition bursting the confines of a dynastic allegory.

The style of Holbein's drawings and that aspect of his art which they most vividly embody - a poised and almost detached empiricism matched by an evenhanded, amazingly precise ability to evoke things and bodies - is not naturally adapted to the glorification or deification of human beings. Holbein's tremendously sophisticated brand of northern realism seems both essentially humane and self-effacing before the facts of existence which it so acutely records. This makes it a great leveller. There is no sense of social or religious (or any other kind) of hierarchy in his drawings of people and what emerges from them cumulatively is, rather, a sense of common humanity and common mortality.

Holbein worked at a time of religious ferment and, in his drawings of those people who witnessed at first-hand the beginnings of the Protestant conversion of the British, we may sense the first stirrings of a Protestant aesthetic, or at least the possibility of one: an art focused, with intimidating clarity, on the individual; and focused with such unmannered neutrality on all the individuals who have come within its orbit that its realism may itself suggest a new and incipiently democratic form of piety. To see a number of Holbein's portrait drawings is to see a group of people viewed simply as themselves and in isolated communion with themselves. Beyond that, it is to see everyone, by implication, defined as merely human - no more, no less - in the eyes of God. This is an art which may, to Protestant eyes, suggest a deep and commendable suspicion of hubris and vainglory, a disregard for outward pomp and circumstance, a new reliance on the self and a new emphasis on the individual conscience. Holbein made the human face seem more naked than it had ever done before.

This may explain the curiously timeless appeal of these pictures, the fact that people even now, separated from Holbein's subjects by 450 years, are liable to be surprised by how lifelike they seem. People often think they know people who look just like Holbein's people. This is partly a matter of technique and it has been well observed that, after Holbein, every other portrait painter in the world is liable to seem mannered. (What is perhaps most unique about Holbein's art is the fact that the equivalents he makes for forms are so exact - whether a chalk flush or an ink beard or a tiny irregular void left to suggest a scar - that no matter how close you get to his image these marks refuse, somehow, to disclose themselves as just marks.) But technique is inseparable from attitude, and behind Holbein's fanatically faithful illusionism lies a fanatical concern with what it is to be alive. His humanity, and his interest in the humanity of others, have made his art endure.

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