Gum breaker

Gum breakers are heavy bends that were put into US sheet stamps to prevent sheets from curling. Curling not only caused storage problems but also caused a fair number of spoils when precancels were overprinted on stamps. The Bureau of Engraving and Printing experimented with several methods beginning with the first rotary press issues. Gum breakers usually disappear from used stamps that have been soaked.
 * The first type had 4-5 horizontal gum breakers evident on the gum side. Used up to the 1928 printings.
 * The second distinctive type had only one horizontal gum breaker, rarely two if right on the upper and lower edges of a stamp. It also had many vertical gum ridges, purposeful gum skips if you will. In use 1928-30.
 * The third type had 2-3 breakers per stamp, with gum ridges less prominent or absent. Breakers are often at a slight angle from horizontal. In use 1930 through to the 1960s.
 * Multicolor engraved/gravure stamps from the 1960s and later can have horizontal and vertical gum breakers.

Collectors should be aware that gum breakers have caused paper creasing or have made accidental creasing easier. [[Category:G]]