Rare British Guiana stamp set for New York auction

An exceedingly rare 19th Century postage stamp from a British colony in South America is expected to fetch a record sum at auction.

The 1856 British Guiana One-Cent Magenta could sell for $20m (£11.8m) at Sotheby's in New York on Tuesday.

The stamp has been sold three time before, each time setting the auction record for a single stamp.

It measures just 1in by 1in (2.5cm by 3.2 cm), and has not been publicly exhibited since 1986.

"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 1-cent magenta, 4-cent magenta and 4-cent blue were created, but only the 1-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 is being 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 currently holds the record for a single stamp at auction.