11c Light Green, Perf 10 at Top and Bottom, Transitional 10/11 Perfs at Top and Bottom (511a). Block of four containing four error stamps, left vertical pair Perf 10 horizontally between, right vertical pair with transitional perfs from 10 to 11 half way between, outside perforations all normal Perf 11, Galveston Tex. duplex cancels, rich color and attractive centering, some separations and rejoined perfs, small repaired tear at bottom right

THE UNIQUE USED BLOCK OF FOUR OF THE 1917 11-CENT WITH ALL FOUR POSSIBLE PERF 10 ERROR VARIETIES. ONE OF THE MOST OUTSTANDING RARITIES OF 20TH CENTURY PHILATELY.

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, it is possible for surviving multiples to show a combination of Perf 11 and Perf 10 stamps or transitional perfs on one stamp. The four possible varieties are Perf 10 at top or bottom and transitional Perf 10/11 at top or bottom. This block is remarkable as the only certified example with all four varieties se-tenant and no normal stamps. The Galveston duplex cancel, rather than a precancel, only adds to its rarity.

Ex Johl. With 1983 P.F. certificate. Scott prices a block with two error stamps at $10,000.00. Scott Retail as four singles

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