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Affiliated with the Local History Network of the State Historical Society of Iowa, and the Iowa Museum Association.
When postage stamps were introduced in the United States in 1847, postmasters were required to deface them to prevent reuse. It was left up to them to decide exactly how to do this; clerks would use whatever was at hand including pens.
A popular method was to use cork bottle stoppers dipped in ink. These worked well, but would tend to blot out the entire stamp making it difficult to check the denomination. To improve upon the idea, clerks began to carve a groove across the middle of the cork, making two semicircles. Modifications included two grooves cut crosswise (the four-piece "country pie"), and then two more, for the eight-segment "city pie", and notches cut out of the outer edge to lighten the cancel further.
The carving process sparked the creativity of clerks across the country, and soon thousands of designs appeared, ranging from shields to skulls to stars, geometrical shapes, animals, plants, and devils with pitchforks. Among the most common fancy cancel designs are stars and crosses of varying designs. The Waterbury, Connecticut post office was the master of the practice, and turned out new cancels for every holiday and special occasion. Their "Waterbury Running Chicken" cancel, perhaps a turkey since it appeared close to Thanksgiving of 1869, was used for only a few days and is now the most prized of all 19th century cancels, with covers bringing very high prices.
"Fancy Cancels," Wikipedia. Online: https://en.wikipedia.org/wiki/Fancy_cancel