niello

Any of various black metal alloys, made of sulphur with copper, silver or lead, used to create decorative designs on other metals.

a young woman named Renata, with a gesturing of her dark curls, beckoned him in with a cigarette-case of Russian silver and niello, which sprang open to reveal a collection of “smokes” […]

An impression on paper taken from the engraved or incised surface before the niello alloy has been inlaid.

To decorate (a surface) using this technique.