EXHIBITIONS / Stylist who spread himself too thin: The early scenes of London are great. But the later Whistler diluted his vision along with his paint

THE TATE Gallery's Whistler retrospective has a stylish approach to an artist whose achievement turns out to be well below the first rank. The galleries are arranged, decorated and lit with great care and just the right amount of flashiness. Such an installation aptly responds to the painter himself. Whistler usually looks better with some accompanying artifice, whether that be wallpaper, Japanese porcelain or sympathetic framing, and here there's a 3ft-high band of gold running around the bottom of the gallery walls.

Taking away all the surrounding matter, what are the intrinsic merits of Whistler's work? First of all, poise. Without bringing anything exactly new to the art of painting, Whistler saw very early on that there was as much art in Manet as in Titian and that a modern artist could take what he wished from the Old Masters without obeisance to their example. But his poise was mostly in the manner he threaded his way between more recent influences. He took things from the early French impressionists and from Pre-Raphaelitism too. He saw what he could learn from Millais; and that he needed a relationship to salon painting, the up-to-date and fashionable version of academic art.

Secondly, Whistler was a genuinely fine etcher. Here again he made the most of his times, for the 1860s revival of etching in both France and England coincided with the birth of the avant- garde. Whistler was not a natural painter, and his brush learnt much from his work with the needle. Etching tends to be economical, as though in pursuit of abstraction. It is ill-equipped for chiaroscuro, so avoids strong contrasts of light and dark. Etching is more instinctive than engraving, which is by contrast journeyman's work, and even when botched it has an air of refinement. And etching is rapid. Whistler's English relative Seymour Hayden, who taught him how to etch, always said that each etching should be completed in one session of work.

All these aspects of the etcher's practice have their counterpart in Whistler's use of oil paint. He was never totally at ease with the solidity and compactness of the painting of his time, whether academic or proto-modern. Whistler didn't want that kind of battle with his medium. So he always tried to evaporate pigment or scrape it off once applied. He's the prime example, in the 19th century, of a 'thin' painter. This is not necessarily a fault, but it's difficult to make such thinness into a virtue.

Especially when thinness characterises paintings that were meant to be large and commanding, with the presence of the most magisterial works to be seen in the Royal Academy. The best paintings in the exhibition ought to be Arrangement in Grey and Black: Portrait of the Artist's Mother and Arrangement in Grey and Black No 2: Portrait of Thomas Carlyle, but they are too big. Whistler didn't have enough sway over his conceptions and subjects. The paintings would have worked better if reduced in size, even by as much as a third. I concede, though, that their extended areas of near-monochrome colour are rather wonderful.

His best use of grey is in Harmony in Grey and Green: Miss Cicely Alexander, which reveals his interest in Spanish painting and his unsparing delight in depicting a girl who is dressed like a modern princess but is in a ratty mood. It was painted from life, apparently in more than 70 sittings. Whistler's more deliberated paintings are usually the more interesting ones. This is even more so when the pictures are portraits of girls or young women. He achieved a kind of psychological pressure in them that was liable to shock Victorian sensibilities. The three paintings of girls that Whistler called Symphonies in White all suggest that their subjects have been wearied by some kind of traumatising knowledge.

These careful pictures belong to the early 1860s, when Whistler first brought his knowledge of contemporary French art to London. He considered himself a man who painted in the cause of realism. This attitude led to descriptive paintings of life along the Thames. They are not as good as Courbet, Whistler's first master, but Brown and Silver: Old Battersea Bridge is a beauty and Wapping of 1860-4 is almost magisterial. Taken together with the etchings of working-class life on the banks of the river, we have a substantial set of work. It made Pre-Raphaelite realism look outmoded. Whistler should have continued along this path.

Instead, he embarked on the famous series of paintings known as Nocturnes. This was the point when Whistler first thinned his paint. It was diluted so that he could get it on canvas or panel quickly, but thinness developed into a credo. The exhibition even has Whistler's remark about his technique written on the wall: 'Paint should not be applied thick. It should be like the breath on the surface of a pane of glass.' This is obviously untrue, and the fact is that Whistler's new method led to a fatal weakening of his art.

I reproduce a small, much later painting called Note in Red: The Siesta of 1883. Here's one of the few moments when we glimpse what Whistler might have achieved with brush and unctuous pigment. The paint is freely and loosely pushed around and the handling has personal character. This is what the Nocturnes lacked. They feel like a substitute for painting. They do not have the substance of major art. It is true that the Nocturnes were at the centre of Whistler's aesthetic. That is the trouble, and the reason why his later painting disappoints. The works on paper are exquisite, but late Whistler approached canvas without conviction, and all too often without finesse.

Tate (071-887 8000) to 8 Jan.

(Photograph omitted)