Asked to name his home town, Andy Warhol would whisper, "I come from nowhere." This was true, more or less: Warhol came from Pittsburgh, an industrial city so grim that H L Mencken said it reduced "the whole aspiration of Man to a joke". The word "smog" was coined for Pittsburgh; some critics think Warhol's lurid palette recalled the dyes that made the city's rivers run purple. It was a place to get away from, and, 60 years ago, Andy did.
Yet, little Andrew Warhola never really left town. We think of his 32 Campbell's Soup Cans as New York art, but his own explanation was more local. "I wanted to paint the things my mom had in her kitchen," he said. Warhol may have become the Manhattan artist, but there isn't so much as a plaque to him there. In Pittsburgh – a mecca for Warhol groupies like me and my companion Miles – he has his own bridge.
One of a trio, the Seventh Street Bridge – renamed the Warhol in 2005 – spans the reassuringly un-purple Allegheny. The Three Sisters were voted the prettiest bridges in America when they opened in the 1920s, which would have pleased Andy. (The Rachel Carson Bridge has its own hanging baskets, though, which would not.) The Andy Warhol Bridge leads to the Andy Warhol Museum which, as you'd expect, has a good collection of Warhols. Its star turn is hidden away in a corner of the fourth floor: Silver Clouds, made for a show in New York in 1966.
The clouds are foil pillows, filled with helium and wafted by fans. Walk into their room and they float quietly towards you: like Andy, it's hard to say whether they're gentle or sinister. When I try to free one trapped in a corner, the others move to the far end of the room and cluster. "I think they're looking at us," says Miles. We leave.
As we're driving back downtown, we spot a huge neon ketchup bottle filling and emptying, filling and emptying. The label says "Heinz", a Pittsburgh firm. Very Andy. Warhol's parents were dirt-poor Slovak immigrants: his mother Julia was occasionally reduced to feeding her children on watered-down ketchup. In better times, she gave her Andek a can of soup every lunchtime – always the same brand, always Campbell's. That was when they'd left the slum of Beelen Street for the slightly less dumpy Dawson Street.
And that's where we're headed now, to No 3252 – the meagre brick house where Andy Warhol grew up, where Julia Warhola, tin-opener in hand, supplied him with his material. I toy with the idea of ringing the bell and asking to see the kitchen, but Dawson Street is still a bit rough. Youths in baggy trousers seem to have developed an un-healthy interest in my camera. We smile Englishly and head for the Carnegie School of Art.
Known as Carnegie Tech when Warhol went there in 1945, this is a very weird place. You'd imagine its students to be skinny kids in fright wigs. But no: they are wearing sportswear and – jeez – playing frisbee. In the middle of the campus is a scary, Orwellian skyscraper, 535ft high and built in the Gothic revival style. Pop it is not: how Andy didn't become a Surrealist beats me. His portrait of Andrew Carnegie, the Pittsburgh millionaire, hangs in the cafeteria, and there's a Heinz Tomato Ketchup Box somewhere, though we can't find it. ("I want to be a machine," Warhol once said. Processed food was fine by him.) We get in the car and head out to Bethel Park.
The final irony of Warhol's irony-filled life is that he is buried not in New York but in this bland Pittsburgh suburb, in the St John the Baptist cemetery. As he made no stipulations in his will, his family brought him home. The Warholas were Byzantine Catholics, a sect that uses icons in their worship. Maybe that explains Andy's faith in Pop icons, the Marilyns and the Elvises; maybe, too, his taste for silver and gold.
The cemetery looks down over Route 88 and a tram line. A tree has fallen, narrowly missing the gravestone of Andy's parents. WARHOLA, it says; their son dropped the A in New York. His grave is just down the slope, marked by the same black granite wedge as most others. There's nothing to suggest it holds the bones of one of America's greatest artists, other than the handful of change and can of tomato soup that a mystery fan has left there every month since Andy Warhol died 21 years ago. (He would have turned 80 this Wednesday.) The soup, naturally, is Campbell's.
How to get there
American Airlines (020-7365 0777; americanairlines.co.uk) offers return flights to Pittsburgh from £465. Double rooms at the Courtyard at the Marriott (marriott.com) cost from £88 per night.
Andy Warhol Museum (001 412 237 8300; Warhol.org). Visit Pittsburgh (001 412 281 7711; visit pittsburgh.com).