the horizontal or slightly diagonal impressions created on the <#gum> of <#rotpress=rotary> <#sheetstamp=sheet stamps> by physically "breaking" the gum. Breakers look something like speed-bumps, and were created as part of the <#perf=perforating> process. The intended purpose of breakers was to reduce the tendency of <#pane=panes> to curl. Gum breakers are known in several configurations, and were used from about 1920 until as late as 1970.