Discoveries of a grand but erudite tourist

EXHIBITIONS: Works from Sir Denis Mahon's great collection offer revelations about 17th-century painters - and the scholars of the 1930s

Without the slightest disrespect to Sir Denis Mahon, I point out to readers that he is an elderly man and that his collection of Italian baroque painting represents a British enthusiasm for the seicento that has its roots in the 1930s and has been largely confined to a coterie of academic art historians. The display at the National Gallery is of course most impressive. At the least, it advances everyone's knowledge of the baroque and presents many painters in a new light. More dramatically, it will convince many visitors that Guercino was a great artist. But there's a sub-theme I find interesting, and that's the resolute character of the scholars of Mahon's generation.

This also concerns Michael Kitson. His long and detailed catalogue introduction describes the intellectual world of connoisseurship in the mid-1930s, when Mahon began to purchase and catalogue Italian paintings. At that time, Kitson writes, baroque art was neglected by museums, rarely the subject of scholarship, and not much loved by the general public . Therefore it was potentially a rich field for a young scholar and collector such as Mahon. The NG exhibition, which cannot be understood without Kitson's important essay, keeps returning to this point. It presents some 80 paintings of high museum quality, fascinating for their own sake. But it is also about learning, as implied by the title, "Discovering the Italian Baroque".

Mahon was lucky to have been born with a keen intelligence and a fortune inherited from his banking family. Furthermore, half a century ago the paintings he liked were relatively cheap. Mahon acquired them in some quantity, and with an eye that now appears exceptionally judicious. However, he could not pursue his researches in a vacuum. He needed to test his opinions against other minds. So he was fortunate in another way.

Around the Courtauld Institute, Kitson writes, there was a handful of youngish seicento experts, led by Anthony Blunt and Ellis Waterhouse; while another "cell" of scholars with the same interests was at Burlington magazine, encouraged by its editor, Benedict Nicolson. In 1937 Nicolson published Mahon's first article, "Notes on the Young Guercino".

Michael Kitson obviously feels that there was a temperamental affinity between this small group and the art that they studied. We may say that baroque painting by Guercino, Poussin, and others was learned and more than slightly aloof: so were the "cells" at the Courtauld and the Burlington. Baroque art may contain great personal passions, but emotions are restrained by intelligence and conformity to the established norms. Erudition, thoroughness and severity are to be expected from artists and historians alike. Tumultuous events must be considered; but they take place in the heavens, or the classical imagination, never on the uneducated earth.

Beneath the earth of Trafalgar Square, in the basement galleries of the NG's Sainsbury Wing, are paintings of limpid and unaffected beauty. They are hung beside canvases of somewhat knotty historical significance. I look forward to seeing them all in daylight in years to come; and probably may do so, for Sir Denis has willed his collection to a number of British public galleries. Meanwhile, the paintings one most wishes to see in daylight are intriguing for precisely that reason. The darkness of baroque painting, its reliance on chiaroscuro, still gives the impression of something being withheld from us - however much we are instructed to admire such effects. The baroque art that by its nature escaped darkness was sculpture; but Sir Denis seems never to have bought three-dimensional work.

He has, however, collected drawings. One room of the exhibition is given over to Guercino's work on paper. We already knew that he was one of the great draughtsmen of the 17th century. In other recent exhibitions he was so lively and various as to appear unrestricted by style. Occasionally he drew like a rococo or a romantic artist. I suspect, however, that Mahon prefers Guercino's discipline to his explorations. The present set of drawings has been chosen to complement the central room of the exhibition, in which we find no fewer than 11 of Guercino's paintings. Here, surely, is the most impressive display by a "neglected" old master that we have seen in London for many years.

I reproduce his Cumaean Sibyl with a Putto, a late work, and the more profound the longer one looks at it. How deeply thought was other baroque painting? I do not recognise an intellectual in Salvator Rosa, though feel glad to see his slightly boastful landscapes and the head of a so- called philosopher who looks more like a bandit, or perhaps Rosa himself. Luca Giordano's modelli for a ceiling decoration take up far too much space, but his Venus, Mars and the Forge of the Vulcan is terrific. It has the madness of the classical gods' adulteries and for that reason eludes grave discussion. Guido Reni's The Rape of Europa doesn't make emotional sense either, though it tries to do so. The colour is rather choice.

Sir Denis has entrusted his pictures to the National Arts Collections Fund for distribution among museums he has himself chosen, with the proviso that they are to be returned if the museum in question ever sells any work from its own collection. Contrary to rumour (one which we alluded to ourselves last week), he has not clearly said that paintings are to be withdrawn if entrance fees are charged. He none the less opposes such charges, and the entrance to his National Gallery exhibition is free.

!National Gallery, WC2 (0171 839 3321), to 18 May.