<Li> rouletting: small horizontal and vertical cuts </Li> <Li> diecutting: cut paper to shape using a metal die--used for self - adhesive stamps . </Li> <P> In the early years, from 1840 until 1850, all stamps were issued imperforate, and had to be cut from the sheet with scissors or knife . This was time - consuming and error - prone (as mangled stamps of the era attest). Once reliable separation equipment became available, nations switched rapidly . Imperforate stamps have been issued occasionally since then, either because separation equipment was temporarily unavailable (in newborn nations for instance), to makers of automatic stamp vending equipment (the United States did this in the 1900s and 1910s), as novelties for stamp collectors (particularly when stamps are issued in souvenir sheets), or as errors . </P> <P> In 1847, Henry Archer constructed the first (rouletting) machine, the "Archer Roulette", to separate stamps . His plan, submitted to the Postmaster General on 1 October 1847, was referred to the departments of the General Post Office and the Inland Revenue . Two such machines were built . After experimentation both machines proved to be failures . From one machine a few stamps from Plates 70 and 71 have survived . This machine consisted of lancet - shaped blades working on a fly - press principle and piercing the paper with a series of cuts . </P>

Why do stamps have ridges on the sides
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