NIELLO (the Italian form of Lat. nigellunc, diminutive of niger, "black"), a method of producing delicate and minute decora tion on a polished metal surface by incised lines filled in with a black metallic amalgam. In some cases it is very difficult to distinguish niello from black enamel ; but the black substance differs from true enamel in being metallic, not vitreous. Our knowledge of the process and materials employed in niello-work is derived mainly from four writers, Eraclius the Roman (a writer probably of the 11th century), Theophilus the monk, who wrote in the 12th or 13th century, and, in the 16th century, Benvenuto Cellini and Giorgio Vasari. The design was cut with a sharp graving tool on the smooth surface of the metal, which was usually silver, but occasionally gold or even bronze. An alloy was formed of two parts silver, one-third copper and one-sixth lead ; to this mixture, while fluid in the crucible, powdered sulphur in excess was added ; and the brittle amalgam, when cold, was finely pounded, and sealed up in large quills for future use. A solution of borax to act as a flux was brushed over the metal plate and thoroughly worked into its incised lines. The powdered amalgam was then shaken out of the quills on to the plate, so as to cover completely all the en graved pattern. The plate was now carefully heated over a char coal fire, fresh amalgam being added, as the powder fused, upon any defective places. When the powder had become thoroughly liquid, so as to fill all the lines, the plate was allowed to cool, and the whole surface was scraped, so as to remove the superfluous niello, leaving only what had sunk into and filled up the engraved pattern. Last of all the nielloed plate was very highly polished, till it presented the appear ance of a smooth metal surface enriched with a delicate design in fine grey-black lines. This process was chiefly used for silver work on account of the vivid contrast between the whiteness of the silver and the darkness of the niello. As the slightest scratch upon the metal received the niello, and became a distinct black line, ornament of the most minute and refined description could easily be produced.
The earliest specimens of niello belong to the Roman period. Two fine examples are in the British Museum. One is a bronze statuette of a Roman general, nearly 2 ft. high, found at Barking hall in Suffolk. The dress and armour have patterns partly inlaid in silver and partly in niello. The dark tint of the bronze rather prevents the niello from showing out distinctly. This statuette is apparently a work of the 1st century. The other example is not earlier than the 4th century. It is a silver casket or lady's toilet box, in which were found an ampulla and other small objects, enriched with niello-work.
From Roman times till the end of the 16th century the art of working in niello seems to have been constantly practised in some part at least of Europe, while in Russia and India it has survived to the present day. From the 6th to the 12th century a large number of massive and splendid works in the precious metals were produced at Byzantium or under Byzantine influence, many of which were largely decorated with niello ; the silver dome of the baldacchino over the high altar of S. Sophia was probably one
of the most important of these. Niello is frequently mentioned in the inventories of the treasures belonging to the great basilicas of Rome and Byzantium. The Scala d'Oro in S. Mark's, Venice, loth century, owes much of its refined beauty to niello patterns in the borders. This art was also practised by Bernward, artist bishop of Hildesheim (11th century). In France, too, judging both from existing specimens of ecclesiastical plate and many records preserved in church inventories, this mode of decoration must have been frequently applied all through the middle ages: especially fine examples once existed at Notre Dame, Paris, and at Cluny, where the columns of the sanctuary were covered with plates of silver in the 11th century, each plate being richly orna mented with designs in niello. Among the early Teutonic and Celtic races, especially from the 8th to the 11th centuries, both in Britain and other countries, niello was frequently used to decorate the very beautiful personal ornaments of which so many specimens enrich the museums of Europe. The British Museum possesses a fine fibula of silver decorated with a simple pattern in niello and thin plates of repousse gold. This, though very similar in design to many fibulae from Scandinavia and Britain, was found in a tomb at Kerch (Panticapaeum). Several interesting gold rings of Saxon workmanship have been found at different times, on which the owner's name and ornamental patterns are formed in gold with a background of niello. One with the name of Ethel wulf, king of Wessex (836-858), is now in the British Museum. Another in the Victoria and Albert Museum has the name of Alhstan, who was bishop of Sherborne from 823 to 867. The metal-workers of Ireland, whose skill was quite unrivalled, practised largely the art of niello from the loth to the 12th century, and possibly even earlier. Fine croziers, shrines, fibulae and other objects of Irish workmanship, most skilfully enriched with elaborate niello-work, exist in considerable numbers. From the 13th to the 16th century but little niello-work appears to have been produced in England. It is, however, in Italy that the art of niello-work was brought to greatest perfection. During the whole mediaeval period it was much used to decorate church plate, silver altar-frontals and the like. The magnificent frontals of Pistoia cathedral and the Florence baptistery are notable instances of this. During the 15th century, especially at Florence, the art of niello-work was practised by almost all the great artist goldsmiths of that period. The British Museum possesses the finest existing example of 15th-century German niello. It is a sil ver beaker, covered with graceful scroll-work, forming medallions, in which are figures of cupids employed in various occupations.
BIBLIOGRAPHY.—The Archaeological Journal of 1862 (vol. xix., p. 323) has an excellent monograph on the subject, see also vol. xii., p. 79 and vol. iv., p. 247 ; Labarte, Arts of the Middle Ages (i855) ; Texier, Dictionnaire de l'orfevrerie, p. 1822 (Paris, 1857) ; Lessing, Collectaneen zur Literatur (vol. xii., art. "Niellum") ; C. Davenport in Journal of Soc. of Arts, vol. xlviii. (Igo') .