Bellotto, Bernardo : The Ruins of the Old Kreuzkirche in Dresden (1765)

How does art make mess? The composer Harrison Birtwistle once compared his methods with those of the painter Francis Bacon. If painters want to introduce some chaos or disorder into their work, they can simply, physically, mess things about. They can (like Bacon) fling a handful of paint at the canvas, or attack the surface with a sponge or rag or broom, or even get someone else to do it for them. But with composers, Birtwistle said, it's different. If they want to put disorder into their music, they have to write out every note of it. They can't just make a mess. They have to make it up.

Not every composer would concur. There are other ways of producing musical disorder. You can determine the sequence of notes through rolls of a dice. You can flick ink on to sheet music or (like John Cage) project a map of the night sky on to the empty staves - and make each spatter, each star, into a note.

Alternatively, you can tell the performer to mess it up for you. The first movement of Carl Nielsen's Fifth Symphony comes to a violently conflicted climax. At one point the snare drum, whose part has previously been written out in full, is instructed to improvise "as if at all costs to stop the progress of the orchestra".

A tricky business. In any deliberate attempt to make mess, whether composed in the studio, or improvised in performance, there's the risk it won't be really messy. The would-be mess-maker is liable to fall back into some kind of order, to revert to those pattern-making habits which - for cultural and perhaps biological reasons - are the default mode of the human mind.

People sometimes talk as if the great achievement of art was to impose order on the disorder of experience. Of course there are many different sorts of order, some more interesting than others. But order as such is no great shakes. The real struggle is to avoid it - as anyone knows, who tried as a child to draw a map of an imaginary island, and found that the ins and outs of the coastline kept turning into an unnaturally regular decorative border. The ability to purposely create or imitate irregularity is a form of virtuosity, a mastery against the grain of our inclinations.

Paintings of ruined buildings have many points and pleasures. They can revel in destruction. They can present a melancholy vision of transience and doom. They can demonstrate survival and endurance - because something still stands in spite of being ruined. They can show the gentle return of the manmade to the organic world, as natural decay and overgrowth reclaim a human construct. They can also present a drama of the regular and the irregular. That's the dominant theme of The Ruins of the Old Kreuzkirche in Dresden by Bernardo Bellotto.

The Church of the Holy Cross, the oldest in Dresden, had a catastrophe-prone history. In 1760 it suffered another setback, being shelled by Prussian artillery. The body of the church caught fire and collapsed. The tower survived. But five years later, with reconstruction work in progress, it too mostly fell down.

This is Bellotto's subject, painted on the spot. The shell of the church tower rises out of a heap of its own rubble. The wreckage is fresh. There's been no time for the softening influence of weather and vegetation. The fractures are still sharp, declaring the recent violence. The picture contrasts the standing up and the fallen down, the hard-edged vertical and the spreading amorphous mass.

And everywhere disorder disrupts order. It's a spectacle of various kinds of chaos. There is the general tumbledown shape of the tower, as against its still imaginable upright form. There are the jaggedy details of its fracturing, as against the geometry of the surviving arches and perpendiculars. There's the pile of rubble itself, amore or less regular pyramid, but made up of a random scatter of fragmented masonry and timber. Flanking the disaster area there's a bank of new public buildings, emphatically straight-lined. But away in the distance on the left another irregularity appears, in the skyline silhouette of the older houses.

Some of Bellotto's contemporaries had begun to experiment with direct mess-making. Alexander Cozens in his New Method of Drawing Original Compositions of Landscape showed how to develop landscapes out of rapidly splashed-down blots of ink. But Bellotto's mess-making is not like that. He is the composer who must write out every note. This painted simulation of a credible chaos - the higgledy-piggledy distribution of fallen pieces - is all his own work. He had the sight before him, true. But that wouldn't teach him how to paint it. He had to want to get the messiness right, and he proceeded perhaps by trial and error, perhaps with the use of some controlled explosions: giving a judder to his brush, or dashing his strokes. The marvel of the scene is not only in the way it preserves a violent catastrophe. It's in the fact that this ruinous mess is all formed by human hand and human judgement - in other words, by an instrument deeply resistant to the production of disorder.

THE ARTIST

Bernardo Bellotto (1720-80) was a Venetian topographical artist who did a lot of work in Germany and Poland. He was one of the great painters of brickwork. He was the nephew and pupil of the artist normally known as Canaletto (whose real name was Antonio Canal), but Bellotto also called himself Canaletto, and this can still cause confusion. Perhaps it was a professional ploy. He doesn't need one now. Recent taste has moved in his favour. Canaletto's sharp sunlit views of Venice, twinkling with spots of bright colour, have been upstaged by Bellotto's more sombre northern townscapes, with their moody lights and silver-grey-green-browns.