Niello is an art of ornamenting metal objects much practised in the Middle ages. The lines of a design are cut in the metal, and filled up with a black lead alloy which gives effect to the intaglio picture.

The art is apparent both in Europe, and Iran, India and Thailand in Asia. It appears that the oldest evidence of the art is Roman, but the work is not exactly similar to that of the Thai niello, instead it is not unlike black enamel work and is called Tula silver. The Thai niello work resembles those from Persia and India and it can perhaps be concluded that the skills in these countries originated from the same source though have developed independently according to each country's culture and taste.

Originally the designs on silver niello were distinct with sufficient space for filling-in of the black lead mixture to give bold effect to the intaglio patterns. Later, however, people preferred a denser pattern, and there was also a development of a combined silver and gold nielloware. The totally gold niello came after that.

The silver and gold combination work is primarily silver niello with parts of the designs plated with gold. The plating is by the classical process of painting the patterns with a gold-mercury paste and subliming the mercury with a hot flame leaving only a plating of gold on the patterns.

For the totally gold niello, the material for the object can be either gold or silver. If it is silver, the designs can be completely gold plated instead of partially as in the gold-silver combination work. A nielloware is generally made of silver or gold since the lead alloy will not adhere to other metals such as copper or bronze.