Possibilities and Limitations of Non-Invasive Analytical Methods in the Examination of Garnet- and Niello-Inlaid Precious Metal Objects – Case Study of Three Polychrome Animal-Style Silver Buckles from the 5th-Century Carpathian Basin

Abstract

The use of non-destructive and non-invasive analytical methods is widespread in the archaeometric study of metal objects, particularly in the case of precious metal artefacts, from which sampling is not, or in a limited way, allowed due to their high value. In this study, we highlight the main advantages and limitations of non-destructive analytical methods used on three polychrome animal-style silver buckles from the mid-to-late-5th-century Carpathian Basin. Optical microscopic observations, handheld XRF, SEM-EDX and μ-XRD analyses were performed to determine the chemical composition of the metals and their decoration (gilding, garnet and niello inlays), as well as the microtexture and mineralogical composition of the niello, in order to gain a better understanding of the materials used and reconstruct the manufacturing techniques in detail. The buckles were manufactured from relatively high-quality silver derived from the re-use of gilded silver scrap metal and intentionally alloyed with brass or leaded brass. The presence of mercury indicated the use of fire gilding. The niello inlays are composed of mixed silver-copper sulphides, even reaching the composition of pure copper sulphide; this is the first time, when copper sulphide niello is observed on a silver object. The almandine garnets most probably originate from Southern India and Sri Lanka. IANSA 2021 ● XII/1 ● 45–67 Viktória Mozgai, Eszter Horváth, Bernadett Bajnóczi: Possibilities and Limitations of Non-Invasive Analytical Methods in the Examination of Garnetand Niello-Inlaid Precious Metal Objects – Case Study of Three Polychrome Animal-Style Silver Buckles from the 5th-Century Carpathian Basin 46 hand, in assessing the presence of any alloying practice and standardisation. From the middle of the 5th century AD, silver became a more important raw material than gold. The combination of these two precious metals provided a new opportunity to enhance the polychrome effect. The use of uncoated gold material or gold plates on silver objects, typical for the Hunnic Period, was superseded by the use of (fire)gilding (Horváth et al., 2019; Mozgai et al., 2019b). In the case of niello, a black silver and/or copper sulphide inlaying material, its artificial, recipe-like character is the key to identify the process of its making and fusing. Dissimilarities in the composition and technology may reflect different goldsmithing traditions or even workshop practices. Since the discussed buckles have close relations with late Roman military equipment in several aspects (Böhme, 1974), determination of the mineralogical composition and microtexture of niello inlays may provide relevant new results. Analytical data are expected to prove or disprove the continuity of the late Roman niello recipes and technology. In contrast with the silver alloy and niello inlay, the garnet inlays represent a primary raw material of natural origin. During data evaluation, no chemical transformation/alteration or human intervention needs to be considered. Therefore, in the case of garnet, we could target the localisation of potential geological sources or the identification of their character (e.g., alluvial or mined garnet). The proportions of major, minor and trace elements, as well as the combination of special inclusions, have proved to be the fingerprint evidence for (certain/particular) garnet Figure 1. The analysed polychrome animal-style rhomboid silver buckles. A: the buckle from Zsibót-Domolospuszta (buckle ZsD) (Janus Pannonius Museum, Pécs); B: the buckle from Bácsordas (Karavukovo) (buckle B/K) (Hungarian National Museum, Budapest); C: the buckle with an unknown provenance (buckle UP) (Hungarian National Museum, Budapest). The tongues associated with the buckle with unknown provenance (buckle UP). D: tongue decorated with a bird’s head; E: tongue decorated with a bird and boar head (photos: E. Horváth). 0 10 cm 0 10 cm