Niello is a black mixture, usually of sulphur, copper, silver, and lead, used as an inlay on engraved or etched metal, especially silver. It is added as a powder or paste, then fired until it melts or at least softens, and flows or is pushed into the engraved lines in the metal. It hardens and blackens when cool, and the niello on the flat surface is polished off to show the filled lines in black, contrasting with the polished metal (usually silver) around it. It may also be used with other metalworking techniques to cover larger areas, as seen in the sky in the diptych illustrated here. The metal where niello is to be placed is often roughened to provide a key. In many cases, especially in objects that have been buried underground, where the niello is now lost, the roughened surface indicates that it was once there. Niello was used on a variety of objects including sword hilts, chalices, plates, horns, adornment for horses, jewellery such as bracelets, rings, pendants, and small fittings such as strap-ends, purse-bars, buttons, belt buckles and the like. It was also used to fill in the letters in inscriptions engraved on metal. Periods when engraving filled in with niello has been used to make full images with figures have been relatively few, but include some significant achievements. In ornament, it came to have competition from enamel, with far wider colour possibilities, which eventually displaced it in most of Europe. The name derives from the Latin nigellum for the substance, or nigello or neelo, the medieval Latin for black. Though historically most common in Europe, it is also known from many parts of Asia and the Near East.