5c St. Lawrence Seaway invert error single
On June 26, 1959, the United States and Canada issued stamps to commemorate the opening of the St. Lawrence Seaway. The designs for this joint issue were very similar, consisting of the Canadian maple leaf and the American eagle in interlocking ovals, superimposed upon a map of the Seaway, a system of canals that spans the Great Lakes and the St. Lawrence River. The vignettes were printed in blue, and the inscriptions at top and bottom were printed in red.
With the acquisition of the Giori Press in 1955, the Bureau of Engraving and Printing could print up to three colors in a single pass, and it used this technology for the US St. Lawrence Seaway issue. The Canadian issue, however, was printed in two separate passes through a press. In a few cases, the sheets of stamps were rotated 180 degrees prior to the second pass, resulting in an inverted center error. A small number of these were distributed to post offices, some were used in the mails, and collectors bought others.
The Canada Post trimmed plate numbers from panes of stamps distributed to post offices. Plate number singles, blocks, and panes were available only from the Philatelic Bureau. Since the Seaway inverts were only distributed to post offices, there are no plate number blocks or singles.