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SEM–EDS and μ-XRD study of the niello inlays of a unique late Roman silver augur staff (lituus) from Brigetio, Pannonia (Hungary)
Abstract
Niello, a bluish black metal sulphide, was widely used for decoration of metal objects by artisans of the Roman Empire. Our knowledge, however, concerning the exact Roman-period niello technique, the appearance of binary silver–copper sulphide niello-decorated silver objects in particular is very scarce. An extensively nielloed silver augur staff (lituus), a unique find from the territory of the Roman Empire, was analysed non-destructively with SEM–EDS and micro-X-ray diffraction techniques. Five niello types were identified, their chemical compositions range from silver sulphide (Ag2S, acanthite) to binary silver–copper sulphide of Ag:Cu ratio 1:1 (stromeyerite). The augur staff decorated with such heterogeneous niello inlays is the first object ever analysed in this manner. Mineralogical and archaeological arguments link niello heterogeneity to the primary production of the object rather than to any post-production repair. Texture-related mineral phase observations allow closer insight into Roman niello technology. The variable copper content is not to be attributed to some technological innovation. The silversmith simply employed not only silver, but in order to make up for the shortage of silver, also differently debased silver, possibly scrap materials for producing niello. Both production (260–280s AD) and burial (early fourth century AD) periods of the lituus are well-dated, and the object was excavated from an undisturbed sarcophagus. Therefore, our data imply that silver–copper sulphide niello reaching the composition of stromeyerite was used by the Roman craftsmen 200 years earlier than previously studied finds had indicated.
... Among inlaying techniques, niello is a black metal sulfide of one or more metals that can be fused or inlaid into the recess engraved in metal including silver, gold and copper-based alloy. Its origin is still obscure 18,19 . The first conclusive evidence of niello dates from the first century CE 18,20,21 . ...
... The composition of niello changed over the course of time. During the Roman period, niello was typically composed of the sulfide of one metal, such as silver or copper, for objects made of the same metals [18][19][20] . There is evidence to suggest that silver-copper sulfide was used intentionally at the end of the fifth century CE, and that silver-copper-lead sulfide was used in Eastern Europe from the eleventh century CE 18,20 . ...
... Published niello analyses suggest that silver sulfide was decorated on gold objects between the fourth-fourteenth centuries CE 20,21 . Silver sulfide niello was produced by melting silver and excess sulfur together 19,20,23 . Modern experiments suggest that silver sulfide can only be applied to a metal recess in solid form because silver sulfide is easily decomposed before reaching its melting point (861 °C) in an oxidizing atmosphere; it is thus practical to heat the niello to about 600 °C to soften it, after which it can be applied 20,21,24 . ...
Northern dynasties (386–581 CE) of China witnessed extensive cultural contacts with the outside world. Several gold objects of this period indicate multiple cultural influences. However, very few of
them were testified by metallurgic analysis. The gold jewellery including a finger ring and an earring with exotic features were uncovered from the joint elite Sogdian tomb of Shi Jun and his wife of the Northern Zhou dynasty (557–581 CE) in Xi’an. The current study applied multiple non-destructive analyses to investigate the decorative techniques and materials of the two objects. the results showed
that both ornaments were made of refined gold. Autogenous welding and brazing were employed for joining the granules of the earring, indicating different technical choices. More interestingly, niello made of silver sulfide was identified as an innovative technology to decorate the finger ring, presenting the earliest evidence of niello inlay in ancient china. it is noteworthy that powders of silver and sulfur were applied separately, deferring from the traditional method of silver sulfide being synthesised prior to being used. These findings help us gain insights into understanding the technical features of early Medieval gold jewellery, as well as the goldsmith’s methods and intentions.
... Five niello types were identified, their chemical compositions range from silver sulphide (acanthite) to binary silver-copper sulphide of Ag:Cu ratio 1:1 (stromeyerite). Type 1 niello is homogeneous polycrystalline silver sulphide (acanthite, Ag 2 S); Type 2 niello is inhomogeneous silver-copper sulphide (exsolution of acanthite, Ag 2 S and jalpaite, Ag 3 CuS 2 ); Type 3 niello is homogeneous polycrystalline silver-copper sulphide (jalpaite, Ag 3 CuS 2 ); Type 4 niello is inhomogeneous silvercopper sulphide (exsolution of jalpaite, Ag 3 CuS 2 and mckinstryite, Ag 5 Cu 3 S 4 ); and Type 5 niello is homogeneous polycrystalline silver-copper sulphide (stromeyerite, AgCuS) (Figs. 4-5.) (Mozgai et al. 2019). Grybeck & Finney (1968) for jalpaite (Ag 1.55 Cu 0.45 S-Ag 1.5 Cu 0.5 S); Skinner et al. (1966) and Kolitsch (2010) for mckinstryite (Ag 1.18 Cu 0.82 S-Ag 1.25 Cu 0.75 S) and Frueh (1955) and Tokuhara et al. (2009) for stromeyerite (Ag 0.9 Cu 1.1 S-Ag 1.0 Cu 1.0 S), respectively. ...
... Based on archaeological arguments the augur staff is well-dated to 260-280s AD and was presumably buried with the last augur of Brigetio in the early decades of the 4 th century AD (Barkóczi 1965;Mráv 2010a;2010b). Both mineralogical and archaeological arguments link niello heterogeneity to the primary production of the object rather than to any post-production repair or post-burial corrosion processes (Mozgai et al. 2019). The variable copper content of the niello decorations of the augur staff indicates no technological innovation. ...
... The variable copper content of the niello decorations of the augur staff indicates no technological innovation. The silversmith simply employed not only silver but in order to make up for the shortage of silver also differently debased silver, possibly scrap materials of the workshop for producing niello (Mozgai et al. 2019). The elevated copper content of niello inlays shows that silver-copper sulphide niello, even stromeyerite (AgCuS), was used by the Roman craftsmen two-hundred years earlier (last third of 3 rd century AD) than the previous studies indicated (end of 5 th century AD). ...
X-ray diffraction (XRD) is a widely used method to specify the mineralogical composition of archaeological artefacts, e.g. the material of inlays or corrosion products of metal objects. Laboratory micro-XRD instruments, like the RIGAKU DMAX RAPID II micro-X-ray diffractometer (μ-XRD), can be used instead of conventional X-ray (powder) diffraction analysis if sampling is not or just limitedly allowed due to e.g. the high value of the archaeological object. In these cases, in situ non-destructive measurements directly on the object or on the detached, small-sized samples are preferred. The possible application of this laboratory micro-XRD instrument in the analysis of archaeological metal objects is demonstrated on the example of three case studies. In order to reconstruct the manufacturing technique of Roman-period niello (black metal sulphide), niello inlays of a late Roman silver augur staff were analysed. Due to the uniqueness and high value of the well-dated and intact object, only non-destructive analytical methods were permitted. Based on the SEM-EDS and μ-XRD results, five niello types were found on the object: pure silver sulphide and different silver-copper sulphides (with silver/copper ratio from 3:1 to 1:1). The object was originally decorated with these diverse niello inlays indicating that silver-copper sulphide niello, even stromeyerite (AgCuS), was used by the Roman craftsmen two-hundred years earlier (last third of 3 rd century AD) than the previous studies indicated (end of 5 th century AD). Corrosion products of a large-sized, late Roman copper cauldron were examined in order to characterise the burial environment. The corroded metal samples taken from the cauldron were analysed in cross section, layer-by-layer, using electron microprobe and μ-XRD analyses. Different corrosion products were identified: copper oxide (cuprite) and copper carbonate (malachite) are the products of passive corrosion indicating burial in a well-aerated, calcareous soil environment, whereas copper chloride (nantokite), copper hydrochloride (paratacamite/atacamite) and copper sulphate (brochantite) are the products of active corrosion forming after excavation. Material and corrosion products of gold and gilded silver objects of the Hunnic Period were analysed by using electron microprobe and μ-XRD analyses. The surface of the high-purity gold objects is covered by a very thin reddish layer, which is a tarnish composed of mixture of gold-silver sulphide corrosion products. The silver objects were completely mineralised into silver sulphobromide and bromian silver chloride (embolite), typical corrosion products of silver alloys buried in soil environment (rich in organic matter). No copper corrosion products were detected indicating that the silver objects were most probably manufactured from high-purity silver alloy.
... Intentional use of binary silver-copper sulphide niello (stromeyerite AgCuS) is assumed to have started only at the end of the 5 th century AD (Moss, 1953;Dennis, 1979;Newman et al., 1982;La Niece, 1983;Oddy et al., 1983;Schweizer, 1993;Northover and La Niece, 2009). Recent studies have proved that silver-copper sulphide niello (reaching the composition of stromeyerite) was already being used in Roman times (Mozgai et al., 2019c). ...
... The use of silver-copper sulphide niello by the craftsmen can be threefold (Mozgai et al., 2019c): (i) unintentional use, when the goldsmith was not aware of the copper content of the silver alloy used for the preparation of the niello; (ii) intentional use, when the silversmith was aware of the variable copper content of the silver alloy available to him, but did not care; and (iii) technological innovation, when the silversmith intentionally prepared a starting silver-copper alloy using a recipe to gain either technological or economic benefits. ...
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 for 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.
Niello is a black material composed of one or more metal sulphides. It contrasts particularly effectively with the metal when inlaid or fused into a recessed design in gold or silver, but is also found on bronze and brass. X-ray diffraction analysis of niello from 180 objects spanning the period between the first century A.D. and the present, from Europe and the Middle and Far East, has established that, as a general rule, Roman niello is composed of the sulphide of one metal only, either silver or copper and, furthermore, the niello is usually made of the same metal as that of the object into which it was inlaid. Sulphides made with silver and copper together were introduced at the end of the fifth century, though silver sulphides were still being made, particularly in the areas dominated by Rome. The manufacture of niello of more than one metal represents a technological advance as, unlike the single sulphides, they can be fused into an engraved design without damaging the metalwork. Lead was added to the ingredients as early as the eleventh century A.D. in eastern Europe. This composition will flow well when melted and therefore can be used to fill more complex designs. Leaded niello superseded the other types almost completely and is still made today. Gold silver sulphide, a hitherto unrecognized type of niello, was found on a number of gold items of various dates.
Although gilt silver threads were widely used for decorating historical textiles, their manufacturing techniques have been elusive for centuries. Contemporary written sources give only limited, sometimes ambiguous information, and detailed cross-sectional study of the microscale soft noble metal objects has been hindered by sample preparation. In this work, to give a thorough characterization of historical gilt silver threads, nano- and microscale textural, chemical and structural data on cross sections, prepared by focused ion beam milling, were collected, using various electron-optical methods (high-resolution scanning electron microscopy (SEM), wavelength-dispersive electron probe microanalysis (EPMA), electron back-scattered diffraction (EBSD) combined with energy-dispersive electron probe microanalysis (EDX), transmission electron microscopy (TEM) combined with EDX, and micro-Raman spectroscopy. The thickness of the gold coating varied between 70–400 nm. Data reveal nano- and microscale metallurgy-related, gilding-related and corrosion-related inhomogeneities in the silver base. These inhomogeneities account for the limitations of surface analysis when tracking gilding methods of historical metal threads, and explain why chemical information has to be connected to 3D texture on submicrometre scale. The geometry and chemical composition (lack of mercury, copper) of the gold/silver interface prove that the ancient gilding technology was diffusion bonding. The observed differences in the copper content of the silver base of the different thread types suggest intentional technological choice. Among the examined textiles of different ages (13th–17th centuries) and provenances narrow technological variation has been found.
The use of silver in ancient civilisations of Mesopotamia, Egypt, Ionia, Greece, Rome and China is presented. Principles of silver corrosion in different environments containing humidity, oxygen, carbonates, sulphur, chlorides, peroxides, ozone and UV, and the morphology of the corrosion layers are described. Cleaning, anti-tarnishing and protection methods are explained. Inhibitor hexadecanethiol (HDT) and a composite coating of Paraloid B-72 containing 2% nano-alumina pigment are tested on silver specimens with tarnished and corroded surfaces and found to be protective when exposed in sulphides and chloride environments in the laboratory, satisfying aesthetic and reversibility criteria. © 2013
On résume les travaux antérieurs sur le nielle et décrit une méthode de préparation pour le laboratoire. On discute le comportement thermique et l'application du nielle sur les métaux, puis on examine sa nature chimique et minéralogique. On propose des tests d'identification qui furent appliqués dans l'examen d'objets datant de l'antiquité jusqu'au XIXe siècle. On arrive à un résultat intéressant: le nielle composé un mélange de sulfures ne fut employé qu'au Xe ou XIe siècle. Auparavant, il se composait d'un seul sulfure, dont l'application au métal nécessitait l'emploi d'une technique différente de celle utilisée par la suite pour les mélanges de nielle mentionnés dans les œuvres du Moine Théophile, d'Eraclius et de Cellini.
This paper surveys previous research on the history and composition of niello and discusses recipes for niello which are recorded in some mediaeval technological treatises. Analytical results (by X-ray diffraction and X-ray fluorescence in the scanning electron microscope) are then reported for 18 niello inlays in copper, silver or gold objects from a wide range of cultural periods and geographic areas. /// L'article passe en revue les recherches effectuées sur l'histoire et la composition du niel, ainsi que les recettes de niel qui se trouvent dans la littérature technologique médiévale. Les résultats analytiques obtenus (en diffraction X et fluorescence X par microscope électronique à balayage) sont présentés pour 18 incrustations de niel existant sur des objets de cuivre, d'argent et d'or, d'époques et de sites variés. /// Diese Abhandlung gibt einen Überblick über die vorausgegangene Forschung bezüglich der Vorgeschichte und Zusammensetzung von Niello und diskutiert die Rezepte für Niello, die in einigen mittelalterlichen technologischen Abhandlungen dokumentiert sind. Es wird über analytische Ergebnisse (durch Röntgenstrahlenbeugung und Röntgenstrahlenfluoreszenz im Elektronenabtastmikroskop) für 18 Niello-Einlagen in Kupfer-, Silber- bzw. Goldgegenständen aus einem breiten Umfang an Kulturzeitspannen und geografischer Gebiete berichtet.
Niello, a lustrous blue-black material, consists of one or more metallic sulfides (silver, copper, and lead). It is used to decorate silver, bronze, and gold objects. The history of the use of niello is reviewed, as well as the properties of the various types.
Stromeyerite, below 93° C., forms orthorhombic crystals having space group symmetry Cmcm, with a = 4.06 A; b = 6.66 A; c = 7,99 A. The unit cell con-tains Ag4CU4S4, with each element occupying 4-fold special positions. The Ag is at 000, OO-h ~ ~ 0, and tH. The Cu and S atoms are at Oy-l, 01d-, ~ ~+ y-r, and tl-Y1, where the y parameter for Cu is 0.46 and for S is 0.80. The volumes of the principal BRILLOUIN zones of stromeyerite have been computed. The assumed electron-to-atom ratio will not exactly fill any of the principal zones. Consequently, a small portion of the electrons must be at a higher energy level separated by an energy gap from the others. A defect struc-ture with up to 0.1 of the Ag atoms missing at random is proposed as a possible lower energy structure. This suggestion is in agreement with the experimental data found in the literature on the preparation of synthetic stromeyerite.
One of the more tangible benefits that accrued to Rome from the conquest of an empire was the acquisition of significant mineral resources, significant because Italy, although rich in iron, could not provide a sufficient supply of the whole range of metals needed by the Roman state for coinage and by members of the élite for the luxury artefacts that helped to enhance their social status. Once Rome had gained control over metalliferous regions of the Mediterranean, Romans, and especially Italians, were not slow to become involved in mining overseas, while the state came to gain considerable revenue from the leasing of contracts for the right to exploit state-owned mineral resources.
The hydrothermal technique was applied to the syntheses of ternary metal sulfides, AgCuS and Ag 3CuS 2, using silver, copper, and sulfur powders as starting materials. AgCuS was obtained as a single phase when the starting ratio of Ag:Cu:S was 0.9:1.1:1 in water above 120°C for 10 h except for synthesis condition at 120°C for 60 h and inductively coupled plasma (ICP) analysis revealed that experimental silver and copper contents in products were Ag 0.89Cu 1.10S. At 120°C for 60 h, some unidentified peaks were observed in the powder X-ray diffraction (XRD) pattern and plate crystals of new compound were found in addition to AgCuS particles from the field emission scanning electron microscopy (FE-SEM) image. Pure Ag 3CuS 2 was also prepared by a simple reaction of stoichiometric silver, copper, and sulfur powders above 90°C, and the composition of products was Ag 2.99Cu 1.00S.
Mckinstryite, Cuo.s+aAgi.sS, where 0 > x > 0.02, was found on a specimen collected in 1907 at the Foster Mine, Cobalt, Ont. Mckinstryite is orthorhombic, space group Pnam or Pna2x, a = 14.043 ± 0.005 A, b = 15.677 ± 0.006 A and c = 7.803 ± 0.003 A, € = 32, specific gravity 6.61 ± 0.03. Strongest X-ray powder diffraction lines are 2.606 A(10), 2.070 A(7), 3.062 A, 3.508 A, 2.862 A, 1.948 A(5), 2.407 A(4), and 2.567 A(4). Mckinstryite is named in honor of Hugh Exton McKinstry, 18961961, late Professor of Economic Geology, Harvard University.
This system is characterized by several phases with highly disordered cation sites, extensive solid solutions, and reaction rates so rapid as to be unquenchable. Ternary compounds, occurring only along the join Cu2S-Ag2S, are jalpaite (Cuo.45Ag1.55S), stromeyerite (CuAgS) and Cuo 8Ag 1-2S. Although orthorhombic chalcocite (Cu 2S) can dissolve up to 1.87 ± 0.37 mol % Ag 2S at 63° C, at high temperatures a cation-disordered, non-quenchable solid solution with a hexagonal closest packed (hep) structure exists from Cu 2S to (Cuo.9 6Ag 104)S. Chalcocite becomes hexagonal at 103.5° C and stromeyerite inverts to the same hep structure at 93.3° C. The eutectoid between chalcocite and stromeyerite is at (Cuj 76Ag 024) S and 67° C. Cu 08Ag 12 S breaks down at 94.4° C to jalpaite + (Cu 096Ag 1-04)S. Jalpaite inverts at 117° C to a copper-rich argentite with a body-centered cubic (bee) structure. At 420° C and 593° C, respectively, Cu2S and Ag2S invert to face-centered cubic (fee) phases with structures identical to that of "high-digenite. " The fee phase has a lowest temperature of stability of 115° C at a composition of (Cu 0 Agx 12)S. Above this temperature the field expands across the Cu 2S-Ag 2S join and also towards more sulfur rich compositions, replacing all other phases including digenite. After the inversion of sulfur-rich argentite at 622° C, a broad fee field extends as a belt across the ternary diagram. Examination of assemblages with bulk compositions in the system Cu-Ag-S indicates that in nature, as in the laboratory, reaction rates are rapid. The former existence of high temperature phases has been demonstrated by the preservation of pseudomorphs and can be inferred from certain textural evidence.
The previously unknown crystal structure of mckinstryite, originally described as Ag 1.18 Cu 0.82 S or (Ag,Cu) 2 S, was solved and refined using single-crystal X-ray diffractometer data collected from a sample from the Clara mine, Black Forest (Mo- K α radiation, CCD area detector, R 1( F ) = 3.85%). Mckinstryite has the refined formula Ag 4.92 Cu 3.08 S 4 or Ag 1.23 Cu 0.77 S (idealized Ag 5 Cu 3 S 4 or Ag 1.25 Cu 0.75 S) and crystallizes in space group Pnma (no. 62), with a = 14.047(3) Å, b = 7.805(2) Å , c = 15.691(3) Å, V = 1720.3(7) Å ³ , Z = 8. The structure contains five Ag, six Cu and eight S sites in the asymmetric unit. One of the Ag sites shows minor Cu-for-Ag substitution. The topology is based on flat, interrupted (010) layers of Cu and S atoms (all atoms on y = 0.25), in which the Cu atoms show triangular or two-coordination to S (interrupted {6,3} tiling). These layers alternate with uneven layers consisting of Ag atoms showing irregular three- to two-coordination to S. Some fairly short Ag–Cu contact distances (2.781–2.884 Å) strongly indicate that metal-metal interaction plays an important role in mckinstryite. The topology is related to that of stromeyerite (∼AgCuS) which contains complete flat layers of Cu atoms triangularly coordinated to S atoms, alternating with layers of loosely packed Ag atoms.
A critical evaluation of literature data on the chemical composition and unit-cell parameters of mckinstryite confirms the presence of a small compositional range of mckinstryite which extends approximately from Ag 1.18 Cu 0.82 S to Ag 1.25 Cu 0.75 S, with the presently studied sample being fairly Agrich. The accurate limits of this range at ambient temperature are still to be determined.
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