The finest known US 1918 24c Inverted Jenny stamp is selling at Robert A Siegel in New York.
The stamp (position 57 on the original sheet) was bought by renowned collector Robert Zoellner as a replacement for his first Inverted Jenny when it was sucked up by a vacuum cleaner.
When he sold it on at Siegel in 1969 it made $192,500. In 2005 it sold for the then world record price of $577,500.
Siegel comments: "This stamp has always been regarded as one of the finest from the original discovery sheet of 100. It is the only inverted jenny to have met the rigorous standards for the xf-superb 95 grade."
In 2007, it was surpassed in value by the specimen that appears next to it on the sheet (position 57), which realised $977,500.
The present lot is valued at around $1.6m, a considerable advance on the record.
The Inverted Jenny is the most famous US error stamp.
It's also one of the rarest, with the entire run being limited to a sheet of 100 found in a post office in Washington DC.
The sheet was later broken up into smaller blocks and singles, the condition of which varies dramatically.
An Inverted Jenny stolen 60 years ago was recently identified. You can read the full fascinating story here.
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