Don't look back: Walter Sickert's Venice

Walter Sickert was already 35 years old when, in 1895, he painted the first of the many pictures of Venetian scenes that you can see in this exhibition at the Dulwich Picture Gallery in London.

Although long resident in the capital, he'd spent much of his life outside England – in Paris, for example, where he had struck up a close friendship with the irascible Edgar Degas. The greatest influence upon his young life to date had been that of James McNeill Whistler, the American expatriate who had demonstrated to his young disciple, between bouts of watching him sweep out the studio, that anything, absolutely anything, could serve as a subject matter for a painting. There was no such thing as high or low. Everything was much of a muchness. Everything could be reduced to the pure transcription of sensation by the alchemy of the brush. Sickert, with his master's words ringing in his ears, had already begun to develop a fascination for the low life of London, all those beery men and blowsy women who hung about on street corners or who rolled out of pubs in full, beery cry.

But by 1895 Sickert was on the move again, and this time it was to Venice, and he would go there again and again over the next several years, as this exhibition makes clear to us. In part, he was escaping the strangulating confines of an unhappy marriage, and in part he was in pursuit of new things to paint, and new ways to paint them.

For Sickert, 1895 had been an important year. During that year he had seen an exhibition of Claude Monet's great cycle of paintings of the façade of Rouen cathedral. Sickert had been impressed by what he saw, and when he arrived in Venice, he decided to do something similar. He chose spots that he knew would give him selling opportunities – as ever, he needed to make some money. What better place to position himself than directly in front of the façade of San Marco Cathedral, at thecentre of St Mark's Square? Could there be a more famous or more photogenic a spot than this? Wouldn't the customers come running?

What is most surprising about the series of paintings we can see at Dulwich is both how like and how unlike Monet they are. The two artists undeniably share an obsessive interest in painting the same building, from the same angle of view, over and over again. But a Sickert feels quite unlike a Monet. There is an airiness and a lightness in a Monet that a Sickert never seems to possess. Sickert's San Marco is leadenly, massily pinioned to the insecure earth on which is it is built – and this is in spite of the fact that Sickert is clearly striving to make the building look and feel fantastically airy, almost as if, as with Monet, he is seeking to demonstrate that it was light from which it had been conjured in the first place. What Sickert does in these paintings is to create a facsimile of a cathedral which looks like a great theatre set, something manufactured from balsa wood, and marvellously artificially lit, front, sides and back. But wholly improbable as a thing that might actually be seen.

The show divides neatly into two halves. The first has to do with representing the buildings and sights of Venice, many of which will be known to us from the work of other artists. Very few of these are memorably quirky.

The second half is more characteristically Sickertian, and it shows us an artist who is gradually transforming himself into the painter who, during the later part of the first decade of the 20th century, will paint all those chilling, low-toned studies that we now know collectively as the Camden Town Murders series, and whose gruesome painterly mood once caused the crime novelist Patricia Cornwell to decide, somewhat fantastically, that Sickert himself had been the perpetrator of those terrible crimes.

The second half of the show has to do with people. Sickert, as in London, was drawn to the low life of Venice – the prostitutes, the hopelessly emaciated old woman, the bar tender.

The most successful of these paintings shows Sickert painting women, in pairs, in small rooms. These spaces are so simply, and so sparely furnished, with a bed and little else. Two women sit on a sofa, leaning into each other. Or a woman leans over the end, almost falling into bottomless space. Many of these women seem to wear black, which gives just a delicate hint of vampirism to the scene. Or a single woman lies back on a bed, looking out for some attention. The colours are low-toned duns, bruised blues, and blacks. Sometimes we have to peer hard just to see what there is to be seen, to differentiate figure from ground. Sickert wants it like that, we feel. He wants these scenes to be difficult to scrutinise. It adds to their creepy mystery. It makes us feel uneasy in their presence, as if we perhaps shouldn't have happened upon them in the first place.

There is a considerable erotic charge to some of these paintings but, as yet, the element which injects such horror into those very nasty paintings of the future has not yet appeared on the stage. Man, surly, taciturn, menacingly hob-nailed booted, still stands on the wrong side of the boudoir door. At least he does for now.

Sickert in Venice, Dulwich Picture Gallery, London SE21 (020-8693 5254), to 31 May