\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.
2. The art, process, or method of decorating metal with
   incised designs filled with the black alloy.
3. A piece of metal, or any other object, so decorated.
4. An impression on paper taken from an ancient incised
   decoration or metal plate.

\Ni*el"lo\, n.
An impression on paper taken from the engraved or incised
surface before the niello alloy has been inlaid.