These days Piano comes across as more of a ship's captain than a revolutionary. The impression is enhanced by the setting of the studio which he designed for himself 10 years ago on the rocky promontory of Punta Nave, north of Genoa. From out at sea it looks like a hi-tech variation on the glasshouses that are such a regular feature of the Ligurian coast. From within, over the buzz of a busy architectural practice, the outside looms. Pot-plants carry green in from the cultivated terraces beyond, and the tilted sightlines converge inevitably on the waves below, whipped up today by a high wind. Piano makes a sweeping gesture as if he is about to tell me that one day all this will be mine. Instead he says, "That is my Internet".
Museums - now the focal point of so much architectural creativity - have been a constant in Piano's work. More than any other architect of the past three decades - except perhaps the Chinese-American Louvre pyramid man, I M Pei - he has used the museum, or cultural centre, as a kind of sounding-board for his peculiarly fluid concept of the relationship between building and user. The Pompidou Centre, currently being refurbished before its reopening at the start of the year 2000, was just the beginning. "For years," Piano says, "museums had been dusty, grey places. We had to profane this idea, open up the museum to everyday life."
When in 1988 he was awarded the Pritzker Prize - a kind of Nobel prize for architecture - Piano was invited to give a speech at a reception hosted in the White House by President Clinton. One of the points he made is bound to surprise those who have considered the Pompidou Centre to be an act of violence perpetrated on the fabric of a historic city. "Architecture," he said, "is a socially dangerous art, because it is an imposed art. You can put down a bad book, you can avoid listening to bad music - but you cannot miss the ugly tower block opposite your house."
A note of mature repentance for the sins of youth can be detected when Piano admits that "perhaps the Pompidou Centre's excessive popularity has undermined one of the reasons why it's there - which is to help people contemplate art. But that doesn't mean I'm not proud of it."
Certainly, the Italian architect's first museum commission after Beaubourg - the Menil Collection in Houston, Texas, completed in 1986 - could not have been more different from that urban spaceship. It is a subtle, almost self-effacing building: the idea was to create a neutral, unobtrusive exhibition space filled with diffused light, in which the works on display take centre stage. Piano's comment on it stands in stark antithesis to the Pompidou effect: "The intention was to foster a sense of absorption, rather than astonishment." As in many of his projects, the key was a single, repeated structural element: a series of lightweight, curving "leaves" that run the length of the ceiling, filtering the light. This was largely the brainchild of the late Peter Rice, the British creative engineering genius from the Ove Arup studio who worked with Piano on almost all of his major projects from Beaubourg on.
Repetition with variations is also central to one of Piano's most original and unlikely projects of recent years - the Tjibaou Cultural Centre in Noumea on the Pacific island of New Caledonia, which consists of a number of tall, open-faced huts made from local materials such as iroko wood and bamboo. The huts - each of which resonates with a different sound when the wind blows - host exhibition spaces, a library, a school and a dance space, all for the local Kanak community. "I can never be prudent when I work," is Piano's comment on these temples in the jungle. "What really attracted me here was this culture of lightness, of the ephemeral, that you find right around the Pacific rim. For the Kanaks, there is no such thing as eternal, unchanging permanence. Permanence is created by the repetition of a gesture."
The Menil Collection in Houston and the Beyeler Foundation Museum in Basel - were designed by Piano to house fixed collections. In the Basel museum, nothing was left to chance: the placing of a series of Giacometti statuettes, for example, was drawn into the architect's blueprint.
Other projects have been more flexible and open plan. Such was the case, for example, in the Piano Workshop's reclamation of the old port of Genoa between 1988 and 1992, with the renovation of four bonded warehouses for use as multi-purpose exhibition spaces.
Piano's interest in buildings that house art is by no means a mined-out seam. He has just won a competition to build a new Paul Klee Museum in Bern, Switzerland, and is engaged in no fewer than three museum rennovations: the Art Institute in Chicago, the Harvard University Art Museum, and the Pompidou Centre - which, he says, needs "a rest and a rethink" after 25 years in which it has been visited by 150 million people.
Above our heads, balanced like a Calder mobile, is a long, thin, delicate model that looks like a computer-generated dinosaur skeleton. It is a section through the roof of Kansai airport, Piano's most ambitious single building project to date, built on a three-mile-long artificial island in the Bay of Osaka in Japan. The new airport opened for business in 1994 and yet even now - as Piano is keen to point out - "seven to eight thousand people go there every day just to look at the building, not to get on a plane".
Kansai was a mere six years from drawing-board to inauguration - an extraordinarily short time for such a huge venture. This was partly the result of the Japanese work-rate (as many as 10,000 construction workers were on site at any one time), but but also of Piano's conversion to computer design as an indispensable aid for the modern Leonardo. The Osaka airport is a seamless fusion of architecture and engineering.
A builder's son, Piano likes to think of himself as a master craftsman in the medieval or Renaissance mould. He has said that "the idea that technique and art belong to separate and parallel universes is as harmful as it is recent". Certainly, his studio, the Genoa Building Workshop, comes across as just this, a workshop - with the young, multi-ethnic apprentices at the drawing board, the scraps and samples of different materials from bamboo to Plexiglass, and, on the ground floor, a real workshop full of carpenters' tools (though one wonders how often they are taken down off their hooks).
The very diversity of Piano's buildings has led some critics to object that, in wiping the slate clean every time, he forfeits claims to a recognisable style. In museum design, especially, the full-on computer-expressionist style of Frank Gehry's Guggenheim Museum in Bilbao or the classical modernism of Richard Meier's Getty Center in Los Angeles have led us to see the big museum commission as a chance for an architect to write his name on the skyline in million-dollar characters.
Piano considers the whole concept of a personal style to be "a dangerous trap ... it's as if the architect is admiring his reflection in the mirror. It means that at a certain point, when you're faced with the adventure of a new project, your signature comes to the fore". He nods at the various models and plans that surround us - an office tower in Sydney, the Harvard museum renovation, the soaring arches of the new Padre Pio pilgrimage church in southern Italy, built in the name of the priest who was canonised earlier this month. "They're so different, because the history, topography, society, structure of these projects are different - it would be absurd to make them all subject to the rule that, first and foremost, the architect needs to get himself recognised."
Asked to play the critic and pick out a characteristic that runs through his whole oeuvre, Piano settles for "lightness". This is not necessarily the first word that springs to mind when considering the new Marlene Dietrich Platz, the centrepiece of Piano's remodelling of the no man's land that used to be Potsdamer Platz in Berlin. A city within the city, funded by Daimler Benz, this area consists of 19 new buildings, 10 new streets, 500,000 square metres of office space, lakes, fountains, two cinemas, a theatre and Germany's biggest casino. And this area is only a part of the entire Potsdamer Platz project - overseen by Piano but with contributions by a number of other architects, including Richard Rogers.
Reflecting on his long-standing friendship with Rogers, Piano decides that "Richard was always the clever one of the duo. I was more of the muddler". But you can see that this is something he values - this building- in of the uncertainty principle. There is a hint of amour propre in his voice when he says, before leaving to clock up some more air miles: "In the end, architecture can never be a perfect, finished thing, where if the ashtray is in the wrong place the effect is ruined."