The relevance of vein texture in understanding the past hydraulic behaviour of a crystalline rock mass: reconstruction of the palaeohydrology of the Mecsekalja Zone,south Hungary

This study reconstructs the palaeohydrogeologic evolution of the shallow‐to‐moderate Mesozoic subsidence history for the Mecsekalja Zone (MZ), a narrow metamorphic belt in the eastern Mecsek Mountains, Hungary. Brittle deformation of the MZ produced a vein system with a cement history consisting of five sequential carbonate generations and one quartz phase. Vein textures suggest different fluid‐flow mechanisms for the parent fluids of subsequent cement generations. Combined microthermometric and stable‐isotope measurements permit reconstruction of the character of subsequent fluid generations with different flow types, as defined by vein textures, yielding new information regarding the hydraulic behaviour of a metamorphic crystalline complex. Textural observations and geochemical data suggest that fracture‐controlled flow pathways and externally derived fluids were typical of some flow events, while percolation through the rock matrix and the relationship to the Cretaceous volcanism and dyke emplacement were typical of others. The difference in the mode of calcite deposition from pervasive fluids (i.e. pervasive carbonatisation along grain boundaries versus deposition in antitaxial veins) between two calcite generations related to the volcanism inspired a stress‐dependent model of antitaxial vein growth. Textural and isotope variations in a vein generation produced by the same parent fluid indicate rock‐dependent hydraulic behaviour for different rock types, distinct action of the contemporaneous fracture systems and different extents of fluid–rock interaction. Cathodoluminescence microscopy and fluid‐inclusion microthermometry shed light on the possible role of hydraulic fracturing in the formation of massive calcite. The time of formation was estimated from the isotope composition of the oldest calcite generation and its presumptive relationship with the sedimentary sequences to the north, whereas microthermometry permitted conciliation of the reconstructed flow sequence with the Mesozoic subsidence history of the Mórágy Block (including the MZ).     

DIRECT EVIDENCE OF PRIMARY GLASS PRODUCTION IN LATE BRONZE AGE AMARNA,EGYPT

This paper presents direct archaeological evidence for the primary production of glass at the LBA site of Tell el‐Amarna, in the form of numerous finds of semi‐finished glass. The diagnostic microstructural and chemical composition of these finds is presented alongside macroscopically similar finds, of shapeless lumps of finished white glass. The semi‐finished glass was found to contain numerous inclusions of residual quartz and newly formed lime‐rich crystal phases, but no added colorant. However, several samples of semi‐finished glass have antimony oxide levels comparable to those of finished white glass, suggesting that the opacifier was added to the initial glass‐making batch. The results are discussed in comparison with the evidence for glass‐making from Qantir – Pi‐Ramesse, identifying some close technical similarities, which indicate that the same technological processes were used at both sites for the production of glass.     

Variability in single smelting episodes – a pilot study using iron slag from Uganda

Most archaeometallurgical studies of iron smelting are based on the analyses of slag fragments randomly selected from slag deposits, and assume that these samples are representative of the typical smelting conditions of the given context. However, little archaeometallurgical research has been published to explore the variability in slag composition within a single smelt, or between individual smelts at the same production site. The material used in this pilot study originates from two iron smelting sites identified in the Buganda Kingdom, Uganda, dated to the 18th and 19th centuries AD. The remains represent evidence of the industrial scale iron production that supported the growth and power of the kingdom. The slag survives in large clusters of complete blocks, in some cases weighing over 100 kg, each resulting from a single smelting episode in a pit furnace. A multi-sample analytical approach has allowed an insight into the compositional diversity within the slag from single smelting events, reflecting changing parameters in the smelting systems. The internal variation of the slag blocks is subsequently compared within and between sites, to address issues of standardisation and to differentiate two technological traditions that would appear very similar at the macroscopic level. On this basis, some sampling recommendations are made for future slag block studies.     

Shades of blue – cobalt-copper coloured blue glass from New Kingdom Egypt and the Mycenaean world: a matter of production or colourant source?

Cobalt blue glass has long now been recognised as characterised by a distinct compositional signature within the typical compositional range of Late Bronze Age glass. More recently, a copper-rich variation of cobalt blue glass has been seen throughout Egypt and the Mycenaean world. This paper discusses and defines this glass type based on trace elemental data, examines whether this lighter-shaded cobalt blue glass is a natural or an anthropogenic variant of cobalt blue glass, and identifies its likely production in Egypt. It investigates the role of this type of glass, particularly with regard to the distribution pattern and the significance of its prevalence in the Mycenaean mainland and the Aegean.     

A truly refractory crucible from fourth millennium Tepe Hissar, Northeast Iran

From the Early Chalcolithic to the Late Iron Age, melting and smelting crucibles were usually made from non-refractory ceramic fabrics, which required heating of the charge from within the crucible to avoid collapsing the ceramic itself. In this paper, an unusual melting crucible from Northeast Iran, radiocarbon-dated to the Late Chalcolithic (ca. 3600 BCE), will be presented that significantly changes our understanding of the development of technical ceramics in Southwest Asia. This crucible, made of a highly refractory talc-based ceramic held together by an outer layer of traditional non-refractory ceramic, is to our knowledge unprecedented at such an early date. As will be argued, this ancient crucible was heated from the exterior or from below and not from the interior. This method of firing, combined with the highly-specialized construction technique, makes this crucible so far unique in prehistoric metallurgy, and forces us to re-examine traditional models for the development of technical ceramics and metallurgical practices in the Old World.     

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.     

Hydrothermal palaeofluid circulation in the fracture network of the Baksa Gneiss Complex of SW Pannonian Basin,Hungary

A well‐developed fracture‐filling network is filled by dominantly Ca‐Al‐silicate minerals that can be found in the polymetamorphic rock body of the Baksa Gneiss Complex (SW Hungary). Detailed investigation of this vein network revealed a characteristic diopside→epidote→sphalerite→albite ± kfeldspar→chlorite1 ± prehnite ± adularia→chlorite2→chlorite3→pyrite→calcite1→calcite2→calcite3 fracture‐filling mineral succession. Thermobarometric calculations (two feldspar: 230–336°C; chlorites: approximately 130–300°C) indicate low‐temperature vein formation conditions. The relative succession of chlorites in the mineral sequence combined with the calculated formation temperatures reveals a cooling trend during precipitation of the different chlorite phases (T_chlorite1: 260 ± 32°C →T_chlorite2: 222 ± 20°C →T_chlorite3: 154 ± 13°C). This cooling trend can be supported by the microthermometry data of primary fluid inclusions in diopside (T_h: 276–362°C) and epidote (T_h: 181–359°C) phases. The identical chemical character (0.2–1.5 eq. wt% NaCl) of these inclusions mean that vein mineralization occurred in a same fluid environment. The high trace element content (e.g. As, Cu, Zn, Mn) and Co/Ni ratio approximately 1–5 of pyrite grains support the postmagmatic hydrothermal origin of the veins. The vein microstructure and identical fluid composition indicate that vein mineralization occurred in an interconnected fracture system where crystals grew in fluid filled cracks. Vein system formed at approximately <200 MPa pressure conditions during cooling from approximately 480°C to around 150°C. The rather different fluid characteristics (T_h: 75–124°C; 17.5–22.6 eq. wt% CaCl₂) of primary inclusions of calcite1 combining with the special δ¹⁸O signature of fluid from which this mineral phase precipitated refer to hydrological connection between the crystalline basement and the sedimentary cover.