Black metallic alloy of sulfur with silver, copper, or lead, used to fill designs that have been engraved on the surface of a metal object, usually of silver.
The black sulfides are powdered, and after the engraved silver has been moistened, the powder is spread on it. When the metal is heated, the niello melts and runs into the engraved channels. After the excess niello is scraped away, the surface is polished. The contrast of the black niello against the bright surface produces an attractive decorative effect. During the height of its popularity in the Renaissance, the technique was widely used for embellishing liturgical as well as utilitarian objects. Nielli (objects decorated with niello) were produced in ancient Rome and 9th-century England. In Russia niello work is known as Tula work.