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.
Bayesian statistics, beta regression, compositional modelling, gold alloys, metallurgy, Muisca, pre-Hispanic Colombia, regional archaeological models
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