Niello is a black metallic alloy made up of silver, sulphur, copper and lead.
Sulphur is added to a molten alloy of silver, copper and lead, creating a black sulphide powder. This powder is used to fill channels in metal inlay work, and is then heated, causing the niello to melt and fill the inlay channels.
Once it has cooled, the niello is then polished, giving it a dark gray to black metallic luster that contrasts beautifully against precious metals such as silver or gold.
Niello can easily be confused with enamel, but niello has a metallic luster as opposed to a vitreous enamel luster.
Common motifs in Siamese nielloware include elephants, Buddhas, Mekhala and Kanakhala (the dancing, severed-headed sisters), as well as other Hindu and Buddhist symbolism.