Interactions between silicate and salt melts in LBA glassmaking

A series of glassmaking experiments have been done to explore the influence, if any, of the presence of alkali chlorides in a typical soda-lime-silica glass batch on the final composition of the glass. The experiments have shown that concentrations of chlorides up to the limit of solubility of chlorine in the melt are actively contributing alkali ions to the glass-forming process, and that at higher chloride concentrations in the batch a separate salt melt forms, known as galle. At equilibrium conditions, the alkali ratio in the galle is different from the initial alkali ratio in the batch and differs from the ratio in the co-existing silicate melt. Significantly, there is full exchange of alkali ions between the two melt systems and the addition of pure potassium chloride to a batch containing pure sodium carbonate (=soda ash) results in the formation of a mixed alkali glass and a mixed alkali galle, with complementary alkali ratios. The alkali earth elements (i.e. calcium and magnesium), in contrast, are not taking part in these ion exchange reactions, and seem not to be affected by chlorides present in the batch. These findings are particularly relevant when comparing analyses of different plant ashes with archaeological glasses; the alkali ion ratios between ash and glass are only likely to be similar when no galle is forming together with the glass melt; in the presence of more than a few weight percent of chlorides in the batch, it is likely that the alkali ratio in the glass will be increasingly shifted away from the total alkali ratio in the batch as the chlorine content increases. While the argument is developed specifically for Late Bronze Age halophytic plant ash glasses, the results are likely to be valid in principle also for any other glasses based on halogen-rich batches and containing more than one alkali metal.     

The Production of Lead–Tin Yellow at Merovingian Schleitheim (Switzerland)*

A Merovingian crucible fragment, with internally adhering yellow glass, and yellow glass beads of the same region and period were investigated by non‐destructive XRF, optical microscopy and SEM‐EDS. Although the microstructure and chemical composition of the yellow pigment (lead–tin yellow type II, ‘PbSnO₃’) are almost identical in both the beads and the crucible, in the latter the pigment occurs in a much higher concentration. However, the glass base in the beads and the crucible is very different, indicating that the beads were not manufactured directly from the crucible. Instead, the crucible most likely served to produce lead–tin yellow, which was subsequently mixed elsewhere with a colourless soda–lime glass to produce yellow glass beads.     

Paint It Black: The Rise of Metallurgy in the Balkans

This paper integrates archaeological, material, microstructural and compositional data of c. 7,000 years old metallurgical production evidence with the aim to address the knowledge of the world’s earliest metalworkers. The main focus is placed on copper minerals, ores, slags, slagged sherds and metal droplets coming from four Vin?a culture settlements in Serbia and Bosnia and Herzegovina: Belovode, Plo?nik, Vin?a and Gornja Tuzla, all dated between c. 5400 and 4400 BC. Chemical study of copper minerals throughout all sites points at striking uniformity in selecting black and green minerals from the early days of the settlements’ occupation, some of which predate the metal smelting events. Microstructural examination of metal production debris showed convincing technological similarity throughout c. six centuries of copper making in the studied sites, as well as a consistent choice of black and green ores for metal extraction. We argue that black and green ores were intentionally selected as ingredients for the metal smelting ‘recipe’ in the early stages of Balkan metallurgy based on the knowledge related to their characteristic visual aspects. This finding demonstrates how important the adequate combination of colours was for the early copper metalworkers and suggests a unique technological trajectory for the evolution of metallurgy in this part of the world. It also illustrates the capacity that micro-research carries in addressing the how and why of the emergence of metallurgy, and outlines a methodology for future studies of early metallurgies worldwide.     

Shrinkage,Metropolization and Peripheralization in East Germany

Since around 2000, there has been extensive research on questions regarding shrinkage and urban renewal in Germany after a task force report revealed approximately 1.4 million vacant flats in East Germany. Since then, most towns and cities have been labelled “shrinking cities” there. While from a planning perspective urban decline and also shrinking cities are widely studied phenomena throughout the industrialized world and a substantial literature exists on the phenomenon in Germany, the impact of political debates and normative considerations is under-researched. This paper highlights the role of political–normative ideas of metropolization and societal relations within this complex core–periphery process, elaborating on the concept of peripheralization and calling for further research.     

5,000 years old Egyptian iron beads made from hammered meteoritic iron

The earliest known iron artefacts are nine small beads securely dated to circa 3200 BC, from two burials in Gerzeh, northern Egypt. We show that these beads were made from meteoritic iron, and shaped by careful hammering the metal into thin sheets before rolling them into tubes. The study demonstrates the ability of neutron and X-ray methods to determine the nature of the material even after complete corrosion of the iron metal. The iron beads were strung into a necklace together with other exotic minerals such as lapis lazuli, gold and carnelian, revealing the status of meteoritic iron as a special material on a par with precious metal and gem stones. The results confirm that already in the fourth millennium BC metalworkers had mastered the smithing of meteoritic iron, an iron–nickel alloy much harder and more brittle than the more commonly worked copper. This is of wider significance as it demonstrates that metalworkers had already nearly two millennia of experience to hot-work meteoritic iron when iron smelting was introduced. This knowledge was essential for the development of iron smelting, which produced metal in a solid state process and hence depended on this ability in order to replace copper and bronze as the main utilitarian metals.     

Early copper smelting at Itziparátzico,Mexico

Archaeological fieldwork and archaeometallurgical analysis have identified a Late Postclassic regional centre of copper production in western Mexico. The total output from a single unit of production at the site of Itziparátzico is an estimated ten tons of copper and nearly forty tons of slag over the lifetime of the installation. It is argued that this smelting was based on slag-tapping furnaces, a technology previously unknown from Mesoamerican archaeological sites. The smelting site is in dense woodland with ample fuel supply, some 125 km from the next mining area with documented contemporary ore extraction; the copper produced would have been passed on to the capital, another 60 km away, for further distribution and working. The scale of production at Itziparátzico indicates that copper smelting was done by part-time specialists embedded in a predominantly agricultural economy, and formed part of a centrally organized network of mining, smelting and processing of copper to supply the Tarascan state.     

Explaining the evolution of ironmaking recipes – An example from northwest Wales

Building on insights from previous Darwinian studies of technology, this paper explores the potential of evolutionary models to explain diversity and change in bloomery ironmaking recipes. Bloomery, or direct process ironmaking, involves the solid state reduction of iron oxide to metal and was the predominant means of producing iron in the pre-industrial world. The most archaeologically accessible record of bloomery practice is slag, an essential by-product of the smelting process. Ironmaking recipes can be characterized by their slag chemistry using a combination of multivariate statistics, ternary phase diagrams, and oxide ratios. Models derived from evolutionary theory are used to explain the shape, structure, and trajectories of ironmaking lineages identified from patterns of slag chemistry in terms of invention, selection, and socially mediated constraint processes. The utility of this approach is demonstrated by its application to slag excavated at Llwyn Du, a late medieval bloomery in northwest Wales.     

Western technical traditions of pottery making in Tang Dynasty China: chemical evidence from the Liquanfang Kiln site,Xi'an city

This study is based on the SEM-EDS and LA-ICP-AES analyses of a sample of twenty-nine Tang sancai sherds unearthed from the Liquanfang site, Xi'an city. The results indicate that ceramics with yellowish bodies are calcareous and those with red bodies were made of ferruginous clays. The use of calcareous clay in Tang sancai bodies is otherwise unknown in Chinese history, which suggests that the technique of Tang sancai making at this site might have been influenced by ceramic technology from the Near East or Central Asia. The paper therefore argues that the traditional approach of treating calcareous clay as the main characteristic of pottery made in the ancient Near East or Central Asia is not necessarily accurate. It is likely that some calcareous Tang sancai ceramics were made in the capital city of the Tang dynasty.