11c Light Green, Perf 10 at Bottom (511a). Block of four, bottom left stamp Perf 10, bottom right stamp with transitional perforations from 10 to 11, bright color, neat strikes of circular datestamps

VERY FINE. A RARE BLOCK OF FOUR CONTAINING ONE STAMP PERF 11 AT BOTTOM AND ANOTHER WITH TRANSITIONAL PERFORATIONS FROM 10 TO 11. USED MULTIPLES OF THIS VARIETY ARE RARE.

At a certain point during production one of the perforating wheels became defective. In the course of repairs part of one perforation wheel was inadvertently changed from Perf 11 to Perf 10. Based on the physical evidence of surviving copies, this was the nineteenth row of pins on the wheel.

Many examples of the Perf 10 on One Side rarities show transitional perfs from 10 to 11 or from 11 to 10. This is because the out-of-gauge perforation pins would frequently cross the span of more than one stamp, depending on where the wheel contacted the sheet.

The Perf 10 on One Side varieties span both the 1917 Washington-Franklin and 1922-23 Issues. It is interesting to note that, apart from the 2c, there is no duplication of denomination between the issues. This would seem to indicate that the improperly repaired wheel was in use for only a short period of time, as there was little overlap in production of the issues. Based on dates of issue of the basic stamps, this probably occurred early in 1923.

With 2009 P.F. certificate. Scott Retail as two singles of the variety

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