Definizione

• Rippled Surface.  Parallel rippled curves across the face on one side of a coin caused by grease left on a die or blank; or falling on either during coining; this heats up and imparts somewhat bubbly ridges during the heat of the coining impression. The problem of oil on the surface of either die or blank is the reason why both dies and blanks are treated before coining. Dies are cleaned with compressed air, blanks are metal cleaned. The effect was serious when knuckle-joint presses were used (either the Uhlhorn or Thonnolier presses) as oil spilled or dropped from the knuckle-joint above the bed where the striking took place. So serious was this problem in the 19th century that one firm, Greenwood and Batley, built a coin press with the knuckle-joint under the feed table to offset this problem!

  excerpted with permission from

  An Encyclopedia of Coin and Medal Technology

  For Artists, Makers, Collectors and Curators

  COMPILED AND WRITTEN BY D. WAYNE JOHNSON

  Roger W. Burdette, Editor

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