The Filstrup cover, featuring a rare 1860 90c, is to auction at Robert A Siegel on December 15.
The lot is set to lead the New York sale of the George J Kramer collection with a valuation of $40,000-50,000.
The stamp is the most valuable in the 1851-1857 series, with the result that very few were ever issued and even fewer were used.
 The Filstrup cover is the only known domestic use of the 1860 90c |
The fact that all US stamps were demonetized in 1961 with the outbreak of the civil war further enhances its reputation and value.
The lot is one of six covers to feature the stamp and is the only example sent domestically.
A cover displaying Martha Washington's free frank is another highlight with a $30,000-40,000 estimate.
The lot was sent from Mount Vernon on November 6, 1801.
Martha was allowed to frank her own letters after her husband's death, but only enjoyed the privilege for two years until she died in 1802.
This makes covers bearing her frank highly desirable.
Also available is a cover displaying a pair of St Louis 20c and 10c bears. The combination is rarely seen, justifying a valuation of $30,000-40,000.
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