One-cent magenta stamp
A one-cent magenta postage stamp printed in what was then British Guiana in 1856 is expected to fetch a record price of $10m-$20m (£6m-£12m), Sotheby’s has said.

The stamp is being sold by the estate of John du Pont, a chemical company heir who died aged 72 in 2010 in a Pennsylvania prison where he was serving a sentence for the 1996 shooting of an Olympic champion US wrestler, David Schultz.

Du Pont, whose wealth was estimated at $250m at the time of his 1997 trial, was one of the richest murder defendants in US history.

Sotheby’s said experts from the Royal Philatelic Society London (RPSL) had re-authenticated the stamp, the only one of its kind known to exist, and it would be offered at auction in New York on 17 June.

“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,” said David Redden, Sotheby’s vice-chairman and director of special projects.

“Our estimate on this stamp is $10m to $20m. 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 RPSL’s expert committee, said the stamp printed in what is now 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 RPSL was in 1935, since when several attempts at forging it have been made.

The current auction record for a single stamp was set by the Treskilling Yellow in 1996 at 2.8m Swiss francs (then worth about $2.2m).

The one-cent magenta was printed in British Guiana in 1856 after a shipment of stamps from England was delayed, which threatened to disrupt postal services 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. It entered Britain in 1878, and shortly after that 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 more times before Du Pont, an avid philatelist, paid $935,000 for the stamp at auction in 1980.