Media playback is unsupported on your device Media caption The British Guiana stamp was owned by du Pont chemical empire heir John du Pont 
 
 A very rare 19th Century postage stamp from a former British colony in South America has sold for a record $9.5m (£5.6m) at auction in New York. 
 
 It took only two minutes for the British Guiana one-cent magenta stamp to be sold to an anonymous bidder, 
 
 The stamp had been sold three times before, each time setting the auction record for a single stamp. 
 
 It measures just 1in by 1in (2.5cm by 2.5cm), and had not been publicly exhibited since 1986. 
 
 Sotheby's auction house said that apart from setting a new world record price for a stamp, it was also the most expensive item by weight and size ever sold. 
 
 "Every collecting area has its Holy Grail. For stamps it is The British Guiana," Sotheby's wrote on its website, adding the stamp is often described as the "most famous" and "most valuable" in the world. 
 
 The stamp, printed on magenta paper, bears a three-masted ship and the colony's motto, "We give and expect in return". 
 
 It initially went into circulation when a shipment of stamps was delayed from London and the colony's postmaster asked printers to make three stamps until the shipment arrived. 
 
 A one-cent magenta, four-cent magenta and four-cent blue were created, but only the one-cent stamp is believed to still exist. 
 
 The last owner of the famous stamp was John du Pont, heir to the du Pont chemical empire, who was convicted in 1997 of murdering an Olympic champion wrestler and died in prison in 2010. 
 
 The stamp was sold by his estate, with some proceeds to be donated to the Eurasian Pacific Wildlife Conservation Foundation. 
 
 It last set a record in 1980 when it was sold to du Pont for $935,000. 
 
 An 1855 Swedish stamp which sold in 1996 for $2.3m had held the previous record for a single stamp at auction. 

 The British Guiana One-Cent Black on Magenta stamp is displayed at Sotheby's in London in this file photo taken June 2, 2014. 
 
 A visitor looks at the British Guiana One-Cent Black on Magenta stamp at Sotheby's in London in this file photo taken June 2, 2014. 
 
 NEW YORK A British Guiana One-Cent Magenta postage stamp from 1856, the only one of its kind to still exist, could sell for a record price when it is auctioned on Tuesday evening at Sotheby's, where it is expected to fetch as much as $20 million. 
 
 If it reaches such a hefty price in the one-lot sale, the one-inch by one-and-a-quarter-inches stamp (2.5 cm by 3.2 cm) printed in black on magenta paper will be the most valuable object by weight and size, according to the auction house. 
 
 "It has always been the world's most famous stamp. It is one of these objects around which a huge mystique has grown up over the years," said David Redden, the worldwide chairman of books and manuscripts at Sotheby's. 
 
 "It has a good story. It was discovered by a 12-year-old schoolboy," he added in an interview. "It's unique and is the only stamp of its kind that has survived." 
 
 The record auction price for a single stamp is 2.87 million Swiss francs (about $2.2 million). It was set in 1996 for the Treskilling Yellow. The Swedish stamp is a misprint of an 1855 shilling stamp in the wrong color. 
 
 The British Guiana stamp is being sold by the estate of the late multimillionaire John du Pont, an heir to the du Pont chemical fortune who died in prison in 2010 at the age of 72. Du Pont was serving a murder sentence for the shooting of David Schultz, a champion U.S. wrestler, in 1996. 
 
 Earlier this year, the Royal Philatelic Society of London re-authenticated the stamp, which avid stamp collector du Pont purchased in 1980 for $935,000. The stamp's authenticity was previously verified in 1935. 
 
 The British Guiana One-Cent Magenta is one of the first stamps in the world. In 1856 in British Guiana, now called the Republic of Guyana, the local postmaster asked a newspaper to print some stamps after supplies from Britain, where its stamps were printed, were delayed. 
 
 There are still a few four-cent stamps issued by the South American country, but this is the only one-cent. Until this year the stamp had not been on public view since 1987, according to Sotheby's. 
 
 The stamp was discovered in 1873 by a 12-year-old schoolboy named L. Vernon Vaughan, who was living in British Guiana with his family. He found it among his family papers. 
 
 He kept it in his collection and later sold it to another collector in British Guiana. It surfaced in Britain in 1878 and was then purchased by Count Philippe la Renotiere von Ferrary, a noted stamp collector. 
 
 The count's collection was donated to the postal museum in Berlin and was later seized by France as war reparation from Germany and sold in 1922. 
 
 It was sold several times before du Pont purchased it. Part of the proceeds of the sale will go to the Eurasian Pacific Wildlife Conservation Foundation, which DuPont supported. 
 
 (Editing by Eric Kelsey and Jonathan Oatis)
– The most valuable substance on Earth is now paper—if it happens to have an 1856 British Guiana 1-cent stamp printed on it. The rare stamp, the only one of its kind still in existence, sold for $9.5 million to an anonymous buyer at auction last night, reports the BBC, making it the most expensive item ever sold by weight and price. The price paid is less than half of what Sotheby's expected the tiny one-inch by one-and-a-quarter inch stamp to fetch, but still shatters the world record set by the sale of an 1855 Swedish stamp for $2.3 million in 1996. The stamp—most recently owned by chemical fortune heir John du Pont, who died in 2010 while serving time for the murder of an Olympic wrestler—set world records the previous three times it was sold, most recently in 1980. It was issued when a shipment of stamps to the British colony was delayed and the local newspaper was asked to print some stamps. In 1873, a stamp-collecting 12-year-old schoolboy found it in his family papers. "It has always been the world's most famous stamp. It is one of these objects around which a huge mystique has grown up over the years," an expert at Sotheby's tells Reuters.