定義

• Blacking.  Coloring metal with nitric acid; turns bronze or silver a dull dark color. Inexperienced metal finishers often use this method of metal coloring because of a lack
  of knowledge of patina finishes or other metal finishing methods. Blacking should not be confused with “blackening” (which is an inexact term for oxidation, where a sulfur solution is used to darken metal).

  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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