Of forming, gilding and intentionality in Pre-Columbian goldwork: analytical characterisation of artefacts from the Museo del Oro, Bogotá

The analytical study of ancient metalwork is a useful strategy to characterise past technologies, but in contrast with other American metalworking traditions this approach has been relatively limited in the context of pre-Columbian Colombia. As a contribution to this emerging research area, this paper presents the results of a compositional and technological study on seven gold alloy artefacts from the collections of Museo del Oro, Bogotá D.C., Colombia, focusing on alloy selection, forming technologies and surface treatments. The artefacts come from four different metalworking regions, and include personal adornments, a votive figure, and an unidentified sheet fragment. Surface imaging and microanalyses were carried out by scanning electron microscopy with energy dispersive spectrometry (SEM-EDS). X-ray mapping was undertaken to gain further insight into depth and nature of surface treatments and internal microstructures. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) data was also collected, enabling cross-analytical technique comparisons and the collection of trace element data. The results allow the identification of alloying technologies and forming methods, as well as the characterisation of corrosion products and gilding layers, and discussion of the intentionality of the latter where present. The case studies are discussed in relation to the existing pool of evidence and used to assess the potential for further analyses on the region’s metalwork.Institute of Archaeometallurgical Studies, MSc Scholarship Arts and Humanities Research Council, PhD Studentship, AH/L503897/1 British Academy, SG-5424

Bayesian regional models of gold and copper alloys from pre-Hispanic Colombia

Throughout the two millennia preceding the European conquest of the Americas, the region of present-day Colombia was witness to the emergence and development of highly sophisticated metallurgical technologies. Alloys of gold, silver, copper, and platinum were used in the creation of a wide range of artefacts intended for personal ornamentation, ceremonial use, funerary goods, functional tools, and votive offerings. While our understanding of the region’s societies has been transformed by a century of research highlighting the diversity of its metallurgical practices, many aspects remain less well understood. This is particularly the case when it comes to understanding the variability of alloy selection and use across space. For the first time, this thesis collates all known compositional data (>2,300 object analyses) on archaeological alloys from within the region, dating to before c. 1600 AD. It addresses research questions relating to the role of technological, environmental, and cultural factors behind alloy selection, at two different scales of analysis. The first focuses on an overview of alloy use across the whole of present-day Colombia. The second presents in-depth modelling of alloying practices for one of the metallurgical regions of Colombia, the Muisca (600-1600 AD). These Bayesian models provide a significant contribution to the field of archaeological science, by introducing a novel set of statistical approaches (multilevel, Gaussian Process, and beta regression modelling) that simultaneously account for sampling uncertainties and interdependencies; allow for the explicit modelling of spatial autocorrelation; and accommodate for the compositional nature of analytical data. It is argued that other archaeological research projects working with large-scale, regional datasets have much to gain from adopting similar methodologies that mitigate the risk of reaching incomplete or biased conclusions. The archaeological implications are used to discuss how Muisca metalworking practices were embedded within complex symbolic frameworks and politically and ritually intertwined exchange networks. The cross-regional Colombian analyses, in turn, are used to highlight the importance of pre-Hispanic metal synergies, where the use of both gold and copper was highly interlinked through space. Notable variations of technological practices across space are also witness to the variability of human responses to different environmental and cultural stimuli – with local adaptations not readily explained by dichotomous metal symbolism, or by the local availability of ore sources

Archaeological science, globalisation, and local agency: gold in Great Zimbabwe

Acknowledgements: We would like to thank Dr Godfrey Mahachi, the Executive Director of the National Museums and Monuments of Zimbabwe, for awarding permits for excavations and for studying the objects. We thank members of the excavation team especially Dr. Foreman Bandama, Dr. Tawanda Mukwende, and Dr. Robert Nyamushosho. We would further like to extend our gratitude to Catherine Kneale and Dr. Simon Griggs at the University of Cambridge for facilitating and supporting the laboratory analyses presented in this paper, as well as Julia Montes-Landa for preparing the polished blocks.Funder: National Research Foundation of South AfricaFunder: University of Cape Town; doi: http://dx.doi.org/10.13039/501100007112Great Zimbabwe (CE1000–1600) is world famous for outstanding cultural innovations and localised and globalised entanglement with trans-Africa and trans-Indian Ocean exchange. New excavations yielded fragments of over a hundred gold processing vessels comprising reused pottery and purpose-made crucibles from stratified contexts in the Eastern Ridge Ruins and adjacent areas. Selected samples were studied using archaeological, microscopic, and compositional (SEM–EDS) techniques. All ceramics were made of alumina-rich clays and contain minerals common to granite-derived lithologies typical of the area, although it is possible that particularly refractory clays were selected to make crucibles locally. These technical ceramics were used for refining and collecting gold at high temperature, most likely producing not only relatively standardised ingots but also finished objects. The composition of the gold prills set in crucible slag is consistent with that of natural, unalloyed gold, while the variability in silver levels and minor impurities point to heterogeneous sources of the gold. Considering these finds in their multiple site and regional contexts, and together with complementary threads of information from early reports of antiquarians and looters, we argue that local agency and gold consumption were much more significant than generally assumed. The conclusion to the paper is that Great Zimbabwe’s famous participation in local and global exchanges was backed by internally driven but improvisation laden production and consumption occurring in homesteads located throughout its various settlements. We end by raising a word of caution about oversimplified narratives of globalisation and their archaeological expressions (see Supplementary Material S0 for the abstract in Shona)

Archaeological science, globalisation, and local agency: gold in Great Zimbabwe

Great Zimbabwe (CE1000–1600) is world famous for outstanding cultural innovations and localised and globalised entanglement with trans-Africa and trans-Indian Ocean exchange. New excavations yielded fragments of over a hundred gold processing vessels comprising reused pottery and purpose-made crucibles from stratified contexts in the Eastern Ridge Ruins and adjacent areas. Selected samples were studied using archaeological, microscopic, and compositional (SEM–EDS) techniques. All ceramics were made of alumina-rich clays and contain minerals common to granite-derived lithologies typical of the area, although it is possible that particularly refractory clays were selected to make crucibles locally. These technical ceramics were used for refining and collecting gold at high temperature, most likely producing not only relatively standardised ingots but also finished objects. The composition of the gold prills set in crucible slag is consistent with that of natural, unalloyed gold, while the variability in silver levels and minor impurities point to heterogeneous sources of the gold. Considering these finds in their multiple site and regional contexts, and together with complementary threads of information from early reports of antiquarians and looters, we argue that local agency and gold consumption were much more significant than generally assumed. The conclusion to the paper is that Great Zimbabwe’s famous participation in local and global exchanges was backed by internally driven but improvisation laden production and consumption occurring in homesteads located throughout its various settlements. We end by raising a word of caution about oversimplified narratives of globalisation and their archaeological expressions (see Supplementary Material S0 for the abstract in Shona).Excavations were funded through grants from the National Research Foundation of South Africa and the University of Cape Town to SC. This work was funded by a Newton Mobility Grant from the Royal Society for the project “Archaeological science and globalisation: a case study of crucibles and metallurgical artefacts from Great Zimbabwe World Heritage site” (NMG\R1\180327). Additional funding was obtained from the British Academy Global Professorship Programme (GP1_100569) and from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 101021480, REVERSEACTION project)

Archaeological science, globalisation, and local agency: gold in Great Zimbabwe.

Acknowledgements: We would like to thank Dr Godfrey Mahachi, the Executive Director of the National Museums and Monuments of Zimbabwe, for awarding permits for excavations and for studying the objects. We thank members of the excavation team especially Dr. Foreman Bandama, Dr. Tawanda Mukwende, and Dr. Robert Nyamushosho. We would further like to extend our gratitude to Catherine Kneale and Dr. Simon Griggs at the University of Cambridge for facilitating and supporting the laboratory analyses presented in this paper, as well as Julia Montes-Landa for preparing the polished blocks.Funder: National Research Foundation of South AfricaFunder: University of Cape Town; doi: http://dx.doi.org/10.13039/501100007112UNLABELLED: Great Zimbabwe (CE1000-1600) is world famous for outstanding cultural innovations and localised and globalised entanglement with trans-Africa and trans-Indian Ocean exchange. New excavations yielded fragments of over a hundred gold processing vessels comprising reused pottery and purpose-made crucibles from stratified contexts in the Eastern Ridge Ruins and adjacent areas. Selected samples were studied using archaeological, microscopic, and compositional (SEM-EDS) techniques. All ceramics were made of alumina-rich clays and contain minerals common to granite-derived lithologies typical of the area, although it is possible that particularly refractory clays were selected to make crucibles locally. These technical ceramics were used for refining and collecting gold at high temperature, most likely producing not only relatively standardised ingots but also finished objects. The composition of the gold prills set in crucible slag is consistent with that of natural, unalloyed gold, while the variability in silver levels and minor impurities point to heterogeneous sources of the gold. Considering these finds in their multiple site and regional contexts, and together with complementary threads of information from early reports of antiquarians and looters, we argue that local agency and gold consumption were much more significant than generally assumed. The conclusion to the paper is that Great Zimbabwe's famous participation in local and global exchanges was backed by internally driven but improvisation laden production and consumption occurring in homesteads located throughout its various settlements. We end by raising a word of caution about oversimplified narratives of globalisation and their archaeological expressions (see Supplementary Material S0 for the abstract in Shona). SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12520-023-01811-7.Excavations were funded through grants from the National Research Foundation of South Africa and the University of Cape Town to SC. This work was funded by a Newton Mobility Grant from the Royal Society for the project “Archaeological science and globalisation: a case study of crucibles and metallurgical artefacts from Great Zimbabwe World Heritage site” (NMG\R1\180327). Additional funding was obtained from the British Academy Global Professorship Programme (GP1_100569) and from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 101021480, REVERSEACTION project)

Beyond baselines of performance: beta regression models of compositional variability in craft production studies

Chemical analyses of archaeological artefacts are often used for provenance studies and for assessing whether specific performance characteristics were targeted by craftspeople in the past. Traditionally, the answers to these questions were sought by identifying compositional averages and by studying their correlations with either the geochemical signatures of candidate raw material sources or the corresponding physical or chemical properties of the studied materials. However useful, this approach only exploits part of the potential information locked inside the chemical compositions of archaeological artefacts. We argue that different levels of compositional dispersion observed within and across archaeological assemblages, and in particular changes in them as a function of behaviourally meaningful factors (such as the size, function, or recovery location of the objects), are sources of information in themselves. To gain probabilistic insights into both types of variability (averages and dispersions) simultaneously, we introduce variable dispersion beta regression models for the archaeological sciences. In doing so, we show how adopting the beta distribution provides a significantly improved alternative to previous solutions to modelling compositional data within the field — namely, those involving simple linear regression on log-transformed data. These approaches often result in numerically impossible predictions, whilst beta regression restricts the model predictions between the upper and lower compositional bounds, accounts for the inherently inconsistent variances of compositional data, and explicitly permits the modelling of compositional dispersions as a function of covariates. Finally, we expand upon this toolset by showing how using a hierarchical model specification within the framework accounts for both local variation and more widely shared practices of material processing and procurement concurrently, and alleviates issues to do with sampling uncertainty. We demonstrate the proposed approach with a study of Muisca gold procurement practices (AD 600-1600) in the Eastern Highlands of Colombia, based on a dataset of 243 elemental analyses. The results allow us to argue for intra-regional movements of fresh geological gold imported from a variety of distant sources. We suggest these movements could result from contributions of gold by people converging into the same location for festivities. The approaches taken to modelling compositional data are readily applicable to other sub-disciplines of the archaeological sciences, such as compositional studies of ceramics and glass, or modelling the variability of diets in isotopic studies.Primary funding was obtained from the Arts and Humanities Research Council UK (AHRC), which funded the lead author’s Cambridge AHRC-Doctoral Training Partnership Scholarship (2112128). Additional funding was obtained from the Osk. Huttunen Foundation and the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 101021480, REVERSEACTION project). In addition, we would like to thank St John’s College, University of Cambridge, and the Department of Archaeology, University of Cambridge, for conference funding to disseminate the results of this research