A TECHNICAL NOTE ON NIELLO
R. Newman, J. R. Dennis, & E. Farrell
NIELLO IS A LUSTROUS blue-black substance used to enrich and heighten engraved and chased ornaments and inscriptions on silver, bronze, and gold objects. More rarely, it may have been used as a kind of “ink” on nonengraved surfaces.1 Niello consists of one or more metallic sulfides (sliver, copper, and lead), and, depending upon its precise composition, may either be fused or burnished into place. Surviving classical, medieval, and Renaissance recipes indicate that virtually every possible combination of the three types of sulfides may have been used as niello, although not all of these variations have been identified on objects to date.
In some instances, niello could conceivably be confused with other black substances on metal objects: chemical patinas on copper alloys; lacquers or dark resinous materials; enamel; and so forth. All of these may be readily distinguished from niello by analytical tests.
This note summarizes the history of niello and some of the properties of the various types. For the sake of brevity, various types will be referred to by the metals which have entered into their compositions (e.g., “copper niello” for copper sulfide, etc.)