LONDON (Reuters) - A rare One-Cent Magenta postage stamp printed in British Guiana in 1856 and most recently owned by the estate of a du Pont chemical company heir convicted of murder is expected to fetch a record price of $10-$20 million, Sotheby's said on Monday.
The stamp is being sold by the estate of the late John du Pont, who died aged 72 in a Pennsylvania prison in 2010 where he was serving a sentence for the 1996 shooting of Olympic champion U.S. wrestler David Schultz.
Du Pont, whose wealth was estimated at $250 million at the time of his 1997 trial, was one of the richest murder defendants in U.S. history at the time of his conviction.
Sotheby's said experts from the Royal Philatelic Society London had re-authenticated the British Guiana One-Cent Magenta, the only one of its kind known to exist, and the auctioneer would offer the stamp at auction in New York on June 17.
"It is one inch by one and a quarter inches, it's tiny and when it sells it will be the most valuable object by weight and size ever sold," David Redden, Sotheby's vice chairman and director of special projects, told Reuters.
"Our estimate on this stamp is $10 million to $20 million. That seems like an awful lot, but in the great scheme of things, across the entire collecting world, the most extraordinary objects in every field, that price suddenly becomes a little modest."
Chris Harman, chairman of the Philatelic Society's expert committee, said the stamp printed in what is now called the Republic of Guyana was without peer.
"It's one of the first stamps in the world, 1856, British Guiana was one of the first countries in the world to issue their stamps, and this was a locally printed stamp, of which there are very few Four-Cent, and there's only one One-Cent, so it has gained this iconic status," he said.
It has not been on public view since 1986, when it was exhibited at a stamp show in Chicago. The last time it was certified as authentic by the Royal Philatelic Society was in 1935, since when several attempts at forging it have been made.
The current auction record for a single stamp is 2,875,000 Swiss francs (approximately $2.2 million), set by the Treskilling Yellow in 1996.
Du Pont, who purchased the One Cent in 1980, was a great-great-grandson of E.I. du Pont, who in 1802 founded the chemical firm that bears his name and created one of America's largest family fortunes.
Du Pont was found guilty but mentally ill in connection with Schultz's death. During the trial, his attorney said du Pont suffered from delusions.
The One-Cent Magenta was printed in British Guiana in 1856 after a shipment of stamps from England was delayed, which threatened a disruption of postal service throughout the colony.
The postmaster turned to the printers of the local Royal Gazette newspaper, and commissioned a contingency supply: the One-Cent Magenta, a Four-Cent Magenta, and a Four-Cent Blue.
The sole-surviving example of the One-Cent was first rediscovered not far from where it was initially purchased.
In 1873, L. Vernon Vaughan, a 12-year-old Scottish schoolboy living with his family in British Guiana, found the stamp among a group of family papers bearing many British Guiana issues.
A budding stamp collector, Vaughan added it to his album and later sold the stamp to another collector in British Guiana.
The One-Cent entered Britain in 1878, and shortly after, it was purchased by Count Philippe la Renotiere von Ferrary, one of the greatest stamp collectors in history.
France seized his collection, which had been donated to the Postmuseum in Berlin, as part of the war reparations due from Germany, and sold the stamp in 1922.
It changed hands several times after that before du Pont, an avid philatelist, paid $935,000 for the stamp in a 1980 auction, marking its most recent record-setting price.
"I don't think any of us will probably see it again in our lives, and so that is a milestone," Harman said.
Additional reporting by Joel Flynn; Editing by Alison Williams