#C3a, 24c Carmine rose and blue, Center Inverted, a most attractive example of the most famous error stamp ever produced. The 24c value of the 1918 series of air post stamps was the first air mail stamp ever issued by the United States. Its purpose was to pay the postage for letters traveling by airplane between New York, Philadelphia and Washington, D.C. It was printed in two colors. The central vignette, printed in blue, pictures a Curtiss Jenny bi-plane. The frame is in carmine rose. To produce the stamp it was necessary to pass the sheet through two presses, with one press printing the blue vignette while the second laid down the carmine rose frame. One full sheet of 100 stamps was mistakenly fed into the second press upside down resulting in this error. Actually, it was the frame which was printed upside down and not the center. However, through the years the error has been referred to as the center being inverted- a more dramatic presentation. This sheet was bought in a New York post office by W. T. Robey on May 14, 1918. He then sold the sheet to Philadelphia dealer Eugene Klein on May 25 for $15,000.00, a neat little profit on his $24.00 investment. Klein immediately sold the sheet to the famous Colonel Green sometime between May 25 and June 1. Green broke the sheet up, keeping a portion for himself and having Klein sell the balance for him. Today, approximately 80 out of the possible 100 inverts are accounted for. The example offered here, being position 17, features unusually strong and fresh colors. It also has full original gum that has been lightly hinged. While centered a bit to the bottom right its centering certainly can certainly be classified as very fine for this. There is a trace of a faint diagonal crease that is not at all readily apparent. It is accompanied by both a 1974 Philatelic Foundation Certificate and a very recently acquired 1989 Philatelic Foundation Certificate. An exciting opportunity to own one of the the most famous of all philatelic rarities.