Niello is a term used to describe a black mixture (usually sulphur, copper, silver and lead) that is used to fill/inlay an engraved metallic surface. Niello is most commonly found on silver items such as snuff boxes and cigarette cases. 

Niello boxes can be found in Imperial Russian items such as the snuff-box below which features a metallic floral design with the black niello to contrast the fine metallic lines.