A complete set of 1881 Atlanta trial colour proofs has realised $33,000 at Robert A Siegel.

The single lot collection headlined the United States Stamps auction in New York on September 17.

The stamps were printed for display in the 1881 Atlanta Cotton Exposition

It consists of 463 stamps in various colours and denominations representing the full range of US postal issues up to 1881.

Siegel described it prior to the sale as "incalculably rare" and "the first complete set we have offered since keeping computerized records".

The proofs were printed in full sheets (five of each issue) and displayed at the International Cotton Exposition, which took place in Atlanta's Oglethorpe Park in 1881.

The event was held to develop new methods of cotton cultivation in the aftermath of slavery and to increase tourism to the city, which had a relatively small population of 40,000 at the time.

Altogether, the stamps display up to 14 colour variations and are rarely offered as a complete set. This is primarily due to the fact the sheets were cut and sold individually to collectors at the end of the event.

A huge array of issues from across US postal history were offered, including an 1861 brownish orange 30c reissue that sold for $10,000.

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