There's been so much hype about the National Gallery's Leonardo da Vinci exhibition opening this week that one approaches it with a certain caution.
Can an artist really be this good, let alone one who produced so few works and those in a calibrated perfection that might seem outdated today?
The answer is yes, yes, yes. Forget the hype, ignore all the articles and television programmes blazoning the trail to this show. Just walk into the second room to be faced by the portrait of Cecilia Gallerani, mistress to his patron Ludovico Sforza, holding her pet ermine and looking sideways wistfully into space. On loan from Krakow, it is, like the Mona Lisa (and, to my mind, preferable to it), simply a perfect picture.
You can talk, as Leonardo's contemporaries did, of the harmony of composition. You can point, as art historians do, to the way that your eye is drawn from her hand and pet up to her face, the manner in which she dominates the space, her pale skin and fine features set against a plain background picked up in the black of her necklace, hairband and decorations on her dress. You can comment, as the exhibition does, on the exquisite detail in the costume, hair and the ermine's head. But in the end there is an ethereal quality about the portrait which is above and beyond the jewelled perfection of the parts, a look in the eye of the woman and a grace in her poise which speaks to the idea of beauty as much as the person of the sitter.
It's quite deliberate. Leonardo, a philosopher as much as an artist or rather a creator who saw art as a means of expressing philosophy, was always in search of the ideal. Michelangelo wanted to embrace life in its wholeness, to express the drama and the emotion of it. Leonardo was equally ambitious for totality, but he approached art as an inquirer, an experimenter, endlessly trying to get at the truth of nature through observation of it.
Recent shows have concentrated on his notebook observations and their accuracy. What the National Gallery aims with this show is to reassert him as a painter over and above a proto-scientist. In a sense they are one and the same thing. Observation, calculation and experimentation are the basis of much of his painting as his notebooks and drawing.
A prolific painter he was not. In a career covering 50 years, Leonardo, the bastard son of a Tuscan notary, died aged 67, and seems on the evidence to have started only 20 paintings and completed only 15 or 16. That he failed to do more was a reflection of a man far more excited by the search and discovery than the making use of it. Even a projected treatise on painting in the manner of Aristotle he started but failed to complete. And what he did complete too often rapidly decayed through trying to do too much with existing oil paints. Michelangelo spent his life trying to get due payments out of his patrons. Leonardo spent his life being pursued by them to complete the works for which they had made down payments.
Instead of trying to encompass the great man's whole career, what the National Gallery has done in this exhibition, and triumphantly so, is to concentrate on his 17 years in Milan from 1482 to 1499, most in the service to Ludovico Sforza, when, with a stipend from the Duke and the favour of the court, he was able to set up in his own studio and bend his interests largely to his own whim. It's an approach which has enabled the Gallery to gather together nearly every painting from the period – the show has nine finished works, more than in any previous exhibition since before the Second World War – and to put them together with preparatory drawings, initial cartoons and unfinished works to show just how exact, and exacting, Leonardo's approach to his art was. It is a concentration which has given the project academic credibility and a reason to seek loans.
The paintings, rather than the research, is what most visitors will wish to see, however, and rightly so. As well as the much-travelled portrait of Gallerani, the Gallery has managed to show together for the first time its own Virgin of the Rock from 1491-92 with the Louvre's earlier version, The Virgin and Child with St Anne and John the Baptist from 1486. The French museum has never allowed this picture to travel before, and facing each other across the room the two give a fascinating insight into the way that Leonardo constantly sought to refine and develop the ideas in his works.
Then there's the recently restored and re-attributed Salvator Mundi, somewhat the worse for wear but still forceful in its presence, plus borrowings from the Vatican (the unfinished St Jerome); the Hermitage in St Petersburg (the rather too sweet Virgin and Child); the Pinacoteca Ambrosiana, Milan (an affectionate Portrait of a Young Man); the Louvre again (Portrait of a Woman with a most challenging look); and the Duke of Buccleuch's stolen and recovered Madonna of the Yarnwinder with figures and rocks by the master.
Put together with works from the Queen's incomparable collection of Leonardo drawings, The Burlington House Cartoon and other sketches, and the National Gallery has pretty much got a complete house of the great man's Milan years. It's even showing (in a separate gallery in the main building) the Royal Academy's copy of the much-damaged Last Supper in Milan by Giampietrino from the time of Leonardo's death, and a formidable group of preparatory sketches, to round off the picture.
It certainly makes the case for this being Leonardo's most productive period artistically. Does it also make the case for Leonardo as the greatest artist of the Renaissance or indeed in history, as he would have wished and his contemporaries acclaimed him? He was a more precise observer though not a greater graphic artist than Michelangelo. He was as graceful, though no more so, in his paintings of Virgin and Child than Raphael. He could sometimes be too complex and prepared for his own good. But come the human figure there is just no one like him in the depth of his vision or the genius in capturing the form of the figure and the fall of light upon it. He desired to make painting more real than sculpture, and he succeeded.
It is his sublime representation of beauty that makes him so loved and still so revered. It is not a vast exhibition, just half a dozen rooms of well spaced pictures. But for all the claustrophobia and limitations of the Sainsbury gallery in which it is shown, this once-in-a-lifetime exhibition will not disappoint.
Leonardo da Vinci: Painter at the Court of Milan, National Gallery, London WC2 (020 7747 2885) to 5 February