That's because Utrecht had such close contacts with Italy. All the artists in this exhibition have an Italianate manner in one way or another. They looked to the classical south in a way that their contemporaries in Delft or Amsterdam did not. Once again we are reminded of the remarkable independence of these Dutch city states. Utrecht is not far from Amsterdam - today a train will take you from one place to the other in half an hour. Yet Utrecht had a distinct regional culture in the Dutch Golden Age of the 17th century, and this culture is most clearly identified in highly sophisticated painting. Hence the theme of the National Gallery exhibition. It's far more than a dry exercise in art history - as the show's popularity in America, where its tour began last year, suggests.
Religion was an important aspect of Golden Age Utrecht. Christopher Brown's helpful little book about the show (pounds 7.95) points out that "Utrecht Protestantism was not as extreme in character as elsewhere in the North Netherlands" when the 17th century opened, and that about 35 per cent of its population of 30,000 were Catholics. These Catholics were often leading members of the community. They had schuilkerken (hidden churches), often richly endowed and decorated, whose traditions were tolerated by the city authorities, at least until the rise of ultra-Calvinism with its links to the House of Orange after 1618. Abraham Bloemaert, who was a Catholic and whose generous and suggestive painting inspired so much Utrecht art, was excluded from civic affairs from that date.
Why, if Calvinism was so much in the ascendant, did so many young Utrecht painters, often Bloemaert's pupils, go to Rome? Perhaps because artists were quite a wealthy part of Utrecht society, in a rather small city where it was acknowledged that people could live as they wished behind their own closed doors. This would explain a number of special characteristics of the paintings now in Trafalgar Square. They have the confidence of high and often youthful accomplishment. The plainer Dutch genres of still life and landscape are avoided. The works often have the appearance of cabinet pictures - ie appealing to a patron's private tastes - even when they are of religious subjects. Above all, these paintings are repeatedly and even obsessively concerned with sexual beauty and desire. Utrecht art positively writhes with poised and knowing nudity.
The exhibition opens with Bloemaert's Moses Striking the Rock, a picture dominated not by Moses, who is far in the distance, but by a bare-breasted woman who may derive from classical statuary but also appears to be engaged in a sensual dance. Then Joachim Wtwael has erotic interpretations of the Mars and Venus stories (painted small, on copper grounds) and of other mythological scenes, including a Judgement of Paris.
Wtwael is one of the discoveries, or rather rediscoveries, of the show. He was a superb craftsman and his enclosed, libidinous imagination makes him one of the early masters of modern erotic art. I admire his big, relaxed Andromeda. His subject's lovely nude figure, face and hair suggest that he was painting from life as well as from Italian prototypes. And we get this feeling from other nudes, particularly those by Lisse and Cornelis van Poelenburgh.
Partly clothed shepherdesses, nymphs attending the feasts of the gods, the bathing Diana, Lot's bathing daughters: such subjects appear a little too often. A paradox of erotic art is that it quickly constricts an artist's imagination, as happened with Wtwael and so many of his descendants. A far more dignified painter was Brugghen, whose Flute Player strikes me as the most emotionally genuine painting on display and is a wonderfully assured glimpse of a boy who contributes to another form of art. Its sensitive and vital presence emphasises the fact that there is not enough portraiture, or any other sign of contemporary life, in this exhibition. Whether that was the case with Utrecht painting in general I do not know. But we are certainly looking at artificial painting.
The Utrecht masters were not "natural painters" in the 20th-century sense because their inspiration was in the refinements of Roman mannerism, and also, no doubt, because of the limited and self-regarding nature of their clientele. That does not make them inadequate artists. But it does take some time before one gets used to their calculated graces and learns to sort out one artistic personality from the next. I think Brugghen is the best of them, and his bigger and more formal pictures helped me to engage with religious painting in Utrecht. Dirck van Baburen is a lesser artist, but his Prometheus Chained and The Mocking of Christ have considerable merits. One of course is a classical subject, the other devotional, but they have about the same emotional weight. What did the Utrecht painters actually believe in, apart from their own talents? This is an unanswerable question.
`Masters of Light: Dutch Painting from Utrecht in the Golden Age': National Gallery, WC2 (0171 747 2885), to 2 Aug.Reuse content