?Errors? and ?Freaks? in United States postage stamp production
Full sheet of extensive misperforations, date unknown
Misperforations on strip of 6¢ Eagle Air Mail Issue, 1938
4¢ Dag Hammarskjold invert, 1962
Webster Knight Collection of United States Postage Stamps

Some stamp collectors focus on the ?errors, freaks, and oddities? of misprinted postage stamps. These imperfections illuminate glitches in the production processes. Production mistakes are rare, and enthusiastic collectors have driven up the prices of these flawed stamps. Under Postmaster General J. Edward Day?s oversight, the printing error on the Dag Hammarskjold stamp was famously not corrected in an effort to avoid producing a rarity. He stated: “The Post Office Department is not running a jackpot operation.” What can these stamps reveal about the history or psychology of collecting?