Archaeological excavations at Bosutswe,Botswana: cultural chronology,paleo-ecology and economy

Excavations at the site of Bosutswe on the eastern edge of the Kalahari Desert in Botswana have uncovered over 4 m of deposit ranging in age from CE 700 to 1700. Our research has produced quantitative and qualitative measures of the material and ecological dimensions that structured the everyday actions and behaviors through which social identities were constituted, maintained, and transformed during the period when the polities of Toutswe, Mapungubwe, Great Zimbabwe and Khami rose to power. By examining the material dimensions that underlay shifting relations of production, exchange, and social stratification we are able to contextualize the social judgments that ascribed value to material goods and food ways, while specifying the ways these were used to create and naturalize social relationships and power differentials. Stable isotope analyses, combined with evidence of vitrified dung, further enable us to suggest changes in herd management strategies used by the inhabitants of the site to compensate for ecological changes brought about by long-term occupation, while at the same time enabling them to economically tie subordinates to them as social divisions became more rigidly defined after CE 1300. The cultural and economic changes that took place at Bosutswe thus directly impact our understanding of the social transformations that immediately preceded contemporary configurations of ethnicity in Botswana.     

The production of speiss (iron arsenide) during the Early Bronze Age in Iran

In this paper, analyses of some unusual slag samples from the prehistoric site of Tepe Hissar in northeastern Iran are presented. These slags are the remains of a five-thousand-year-old pyrotechnological process that produced speiss, a quasi-metallic material usually formed as an accidental by-product of copper or lead smelting. We argue that the “speiss slags” from Tepe Hissar suggest the intentional production of iron–arsenic alloy (“speiss”) in prehistory. Why the Tepe Hissar metalworkers produced speiss is a question that requires further investigation, but our preliminary assessment suggests that it was to provide arsenic as an alloying component for arsenical copper, the preferred copper alloy during much of the Early Bronze Age in Iran, and widely used across the ancient world. This recognition significantly advances our understanding of the early stages of metallurgy in the Old World.     

Middle Bronze Age metallurgy in the Levant: evidence from the weapons of Byblos

This paper constitutes a synthesis of a technological investigation on copper base alloy weapons from Byblos. Most of the weapons are typical of the Middle Bronze Age in the Levant. Methods such as metallographic examination and chemical analyses by EDS were used to identify the different stages of the chaîne opératoire used in the making of these weapons. The results reveal precise information regarding the production of several types of weapons such as the type and performance of the moulds used for casting and the deformation process. Furthermore, these results highlight the contribution of economic and cultural factors in the choice of components in a copper base alloy recipe. Finally, the use of silver–copper brazes for joining copper base alloy objects is recorded for the first time for the period and region concerned.     

Microstructural and Componential Characterization of the Plating Technology on Chinese Han Dynasty Bronze Fragments

The bronze wares of the Han Dynasty excavated in Chongqing are decorated with plating patterns, maintaining an exquisite lustre right up to modern times after the covering patina is cleared away. In this paper, a plated fragment of the Han Dynasty from the Wushan County Museum was characterized by combining optical microscopy (OM), scanning electron microscopy with X‐ray energy‐dispersive spectrometry (SEM–EDS), X‐ray fluorescence analysis (XRF), X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS). The results showed that the bronze fragment was gilded with a ~ 3 μm thick gilded layer and a ~ 20 μm thick silvered layer. The high concentration of Hg and Hg‐rich intermetallic compounds confirmed the existence of mercury gilding/silvering technology, for example, Au₉Hg in the gilded layer and Ag₁₃Hg₇ in the silvered layer. An ordered stripe structure was observed in the gilded surface, corresponding to the formation of rod‐like, intermetallic Au–Hg compounds. Specifically, a high concentration of Au was detected in the silvered layer. The exploration of gilded/silvered bronze casts light on this ancient technology and the benefit of identifying, protecting and reproducing it.     

For Whom the Bells Fall: Metals from the Cenote Sagrado,Chichén Itzá

Bells of copper and copper alloys and gold–copper alloys were deposited in events at the Cenote Sagrado at Chichén Itzá, Mexico during the site's primary occupation (ad 750–1050) and in later centuries. Housed in three museums in the United States and Mexico, bells (n = 38) were evaluated for traces of fabrication and alteration using Vis–UV–IR optical microscopy. Bulk compositions were determined through p‐ED‐XRF. Phases and compositional variation by depth were characterized through XRD and RBS. The technological styles of bell groups were ascribed to communities of metallurgical practice, from West and Central Mexico to Costa Rica and Panama.     

The technology of tin smelting in the Rooiberg Valley,Limpopo Province,South Africa,ca. 1650–1850 CE

A substantial indigenous tin-smelting industry arose in the Rooiberg valley of northern South Africa in the second millennium CE. This study concentrates upon tin-smelting slags and refractory ceramics from two archaeological sites that date between ca. 1650 CE and ca. 1850 CE. These were studied by optical and electron microscopy, wavelength-dispersive x-ray fluorescence (WD-XRF), inductively-coupled plasma mass spectrometry (ICP-MS), and electron microprobe (EMPA). The slags are predominantly glassy; high SnO and relatively low SiO₂ contents indicate that tin is a major glass-forming element. Comparison of slag chemistries with the mineralogy of ore deposits and host rocks shows that alluvial cassiterite was used at one of the sites, while cassiterite from hard-rock mining was smelted at the other site. Since few preindustrial tin slags have been studied, we compare our findings to other published examples, mostly from southwest England.     

The effect of soil conditions on the long-term corrosion of buried tin-bronzes and copper

The object of this work was to relate the corrosion of tin-bronzes to the chemical condition of the soil in which they have been buried, most of them since the Bronze Age. Naturally, it was not easy to obtain recent hoards with their related soils, and considerable reliance had to be placed on recorded finds by taking recent soil samples from sites on which hoards were found over a hundred years earlier. Even so, with the exception of peat, a reasonable relationship appears to exist between the pH of the soil and the state of the metal. Acid soils are aggressive to metals and alkaline soils are benign. In no cases were sulphate reducing bacteria active in promoting corrosion. In the main, peat and peaty soils were benign in spite of their acidity, probably due to the protective action of polyphenols.     

Archaeological and chemical evidence for the earliest American use of raw coal as a fuel in ironmaking

The archaeological discovery of bituminous coal in the tipple area and the subsequent analyses of specimens of the iron ore, charcoal, limestone, slag, and cast iron from the Eaton (Hopewell) blast furnace built in 1802 indicate that raw coal was used in combination with charcoal as a fuel in American iron smelting at least thirty years before it was used alone. Further, its use in this combinatory manner marks the earliest as yet attested to in the New World.     

Metallurgical analysis of copper artifacts from Cahokia

Copper artifacts from Cahokia Mounds, Illinois were analyzed from a materials science perspective to shed light on techniques used by Mississippian copper workers to deform nuggets of native copper into thin sheets. Eight small copper pieces from a copper-working site at Cahokia’s Mound 34 were subjected to metallographic examination. Replication experiments thereafter recreated features of the artifacts under controlled conditions. It is concluded that copper sheets were thinned through repeated cycles of hammering and annealing performed at temperatures achievable in an open wood fire. The welding of sheets to create multilayered objects was not observed in any artifacts and could not be accomplished experimentally. Additionally, a possible cutting method used on some artifacts was identified.     

Metallurgical ceramics from Mayapán,Yucatán,Mexico

Recent excavations at the Postclassic (AD 1050–1440) Maya site of Mayapán, Mexico, have uncovered a variety of metal objects, metal production debris, and ceramic objects that appear to be linked to metallurgical activities at the site. Our present study investigates a corpus of small ceramic objects to determine if these objects was used in metallurgical processes such as lost-wax casting. A variety of analytical techniques was utilized, including x-ray fluorescence, electron probe, petrography, and reflected light microscopy. Metal residues were detected on the surfaces of several objects, and copper prills were identified within the ceramic fabric, suggesting that the ceramics were exposed to liquid metal during remelting and/or casting events. A comparison of the microstructures of these metallurgical ceramics to typical ceramics from Mayapán demonstrates that the fabrics are very different, and suggests that the metallurgical ceramics were specifically engineered to function in the high temperature environment required for metallurgy. The distribution of metal and metallurgical ceramics across the site of Mayapán suggests that metal production activities may have been more widely distributed and practiced than earlier thought.