Niello \Ni*el"lo\, n. [It. niello, LL. nigellum a black of
   blackish enamel, fr. L. nigellus, dim. of niger black. See
   Negro, and cf. Anneal.]
   1. A metallic alloy of a deep black color.
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   2. The art, process, or method of decorating metal with
      incised designs filled with the black alloy.
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   3. A piece of metal, or any other object, so decorated.
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   4. An impression on paper taken from an ancient incised
      decoration or metal plate.
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   5. An impression on paper taken from the engraved or incised
      surface before the niello alloy has been inlaid.
      [Webster 1913 Suppl.]