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How does the niello technique create black designs on gold or silver jewelry?

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jewelry Stomacher brooch with emeralds and enamel flowers on gold, from the treasure of the Virgin of Pilar, mid-17th century; in the Victoria and Albert Museum, London.

The niello technique creates striking black designs on gold or silver jewelry through a process of inlaying. First, a design is incised or engraved into the surface of the metal.12

To create the black filler, a metallic alloy—typically composed of silver, copper, and lead—is fused and mixed with sulfur to produce black-colored sulfides. This material is ground into a powder and applied to the engraved metal, which has been moistened with a flux to promote bonding.13

When the piece is strongly heated, the niello powder melts and flows into the engraved channels. Once the metal cools, the excess niello is scraped away until the design is clearly visible, and the surface is polished to a smooth finish. The resulting contrast between the dark, inlaid sulfides and the bright precious metal creates a distinct and durable decorative effect.123