Niello (objects decorated with Niello are called Nielli), also called Tula (Tulaware) is a metallic alloy made by fusing together silver, copper and lead, and mixing the molten mixture with sulfur, creating the familiar grayish-black enamel-like filling. At the height of its popularity, during the Renaissance, the technique was used for the embellishment of liturgical objects, as well as utilitarian objects typically small in scale such as belt buckles, cups, boxes, and cane or knife handles. Nielli were produced by the ancient Romans and were well established in England at an early date, reaching its peak in 15th century Italy at the workshop of a Florentine goldsmith. Russian goldsmiths revived the craft and worked in Tula in the late 18th century, and Niello work came to be known in Russia as Tula work.
Tula’s melting point at approximately 500° C is significantly below that of silver’s at 800° C. In order for the Tula to adhere to the metal object (usually silver), a pattern must be etched/engraved, or cut out of the work piece, leaving gaps. The molten grayish-black colored sulfides are powdered and after engraving on silver is completed, the object is moistened with a flux, and some of the powder is then spread on the object and the metal strongly heated. As the Niello melts, it runs into the engraved channels. The excess Niello is then removed by scraping until the filled channels are clearly visible. The surface is then polished.
The process is very difficult and time-consuming, and this specialty is today virtually lost.