In philately, gum is the substance applied to the back of a stamp to enable it to adhere to a letter or other mailed item. The term is generic, and applies both to traditional types such as gum arabic and to synthetic modern formulations. Gum is a matter of high importance in philately.
History
Before postage stamps existed, people receiving letters would have to pay for them. The payment was based on how many papers were in the envelope and how far the letter had traveled. Rowland Hill came up with a solution of prepayment. This led to his invention of stamp gum in 1837. The world's first adhesive postage stamp was called the Penny Black. Many early stamps were not gummed, however, and some have been unable to be gummed due to shortage (for instance, the typewritten Uganda Cowry stamps of 1895). Extreme tropical climates were also a problem for Curaçao and Suriname. Some stamps, intended only for sale to stamp collectors, have been issued without gum, for instance the United States Farley's Follies souvenir sheets of 1933. On the first stamps of Great Britain the gum was called cement and was made from a mixture of potato starch, wheat...
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