It's flimsy, faded - and the most precious item in the world

This rather tatty looking, stained piece of paper is arguably the most valuable object in the world. A rare Swedish stamp nearly a century-and- a- half old, it was sold for a record 2.9 million Swiss francs (pounds 2.1m) at a public auction in Zurich yesterday.

The Treskilling Yellow, which is listed in the Guinness Book of World Records as the most valuable object of any type by weight, volume and density, has belonged successively to many of the world's top collectors since first going on the market in 1885. It was first sold to a Stockholm dealer for just 7 Swedish kroner (70p) that year by a schoolboy who discovered it among a pile of letters at his grandmother's house.

The sale eclipsed the record of SFr1.9m (pounds 890,000) for the same stamp in 1990 and was bought by an unidentified Stockholm-based dealer. It will be shown at a Thanksgiving weekend exhibition at the Waldorf-Astoria Hotel in New York later this month.

Auctioneer David Feldman who co-ordinated the sale said yesterday that the price went far beyond expectation and predicted that it would give the world stamp-collecting market a major boost.

"It will give a lot of confidence to people who have bought rare stamps," he said. "It's a very special moment in the history of philately."

Predictably, the battle was on in Zurich yesterday to identify the mystery buyer whom many believe is a Stockholm-based dealer.

Bogdan Stanculescu, a Romanian collector and stamp expert, estimated that only a handful of collectors would have the means to buy the Treskilling Yellow, adding that it was possible that the person who bought it wanted to keep it in Sweden.

Mr Feldman said he knew the identity of the collector but declined to identify him. "I have met him before, but I did not know he was going to bid," he added

Hans Lernestal, the Stockholm dealer who bought the stamp for the private client, said he would have been prepared to pay even more for it. "I am very proud to have the honour to purchase the most valuable item in the world," he said.

The Treskilling stamp is the only yellow version of an 1855 three-shilling issue, which is Sweden's first postage stamp. Although in appearance it is in fact a dull, orangey hue, the others that have survived are green, and for many years, yesterday's stamp was believed to be a fake. Scientific tests in the 1970s proved otherwise.

It has held the single stamp record in successive sales since 1984, and its latest owner, Sven-Olof Karlsson of Sweden, decided to sell rather than make final payments on the purchase he made six years ago.

Yesterday's sale took about four minutes, with some 16 bids coming in from more than half a dozen would-be buyers, including one by telephone from Malaysia.

The stamp was discovered by Swedish schoolboy, George Backman, in 1885. During a Christmas visit to his grandmother, 14-year-old George asked her to open a chest of drawers so that he could search for letters, hoping to find some old stamps to sell. He took the yellow stamp and some others to a dealer in Stockholm who agreed to buy it for Skr7.

Recalling the occasion in later years, Mr Backman said: "I dared to ask him whether I was to receive seven crowns for the stamp, whereupon he answered 'I shall pay that much all the same'." Shortly after completing the transaction, Mr Backman discovered that the dealer had already been offered 300 crowns for the rarity, but had declined to part with it, saying: "It will someday reach a very high price."

Stars of the stamp world

The Mauritius "Bordeaux Cover" - a letter sent to wine merchants in 1847 with the one penny and two penny first issues of Mauritius - which was bought for pounds 2.6m in less than a minute at an auction in Zurich in 1993.

A British Penny Black, sold on an addressed envelope, went for pounds 1.3m because the letter had been sent four days before the stamp's official date of issue, 6 May 1840.

A one cent British Guyana stamp dating from 1856. The owner of one of the only two known examples of the "British Guyana one cent" bought the other for about pounds 30,000 and then burnt it - thereby doubling the value of the surviving example. It is now worth about pounds 445,000.