Niello
ni·el·lo | nē-ˈe-(ˌ)lō
noun
An inlay technique in which the grooves made in silver or gold are made black in color by the use of a composition of metal sulfides
Niello is a mixture of several materials to create a black substance that is used in inscriptions and paintings dating back to the Middle Ages. The mixture traditionally contains copper, lead, silver, and sulfur and was most commonly used on silver for inlay in the etched metal. It was also used in gold and some other precious metals. It is heated to be soft and then applied to inlay where it can cool and create a black color that stands out as lettering, artwork, or other ornamentation within precious metals. It was used in rings, pendants, diptychs, and other works of art throughout the Middle Ages and the renaissance, with the technology dating back to the Bronze age. Examples of Niello can be seen in work dating back to 1800 BC in Syria.