We have developed a new theoretical framework within which to analyses these data. This is a dynamic model which focuses not on individual objects but on assemblages of objects, which are created according to the specific question - an assemblage could be all the objects in a tomb, or all the objects of a particular type across Eurasia. The key element is to look at change in the archaeometallurgical record - change over time, or change across space by comparing several contemporary sites. This leads to a new set of tools with which to interpret these data, including an approach known as 'Copper Groups', which uses data on the commonly measured trace elements (arsenic, antimony, silver and nickel) to look at the common patterns of trace elements in the data. A similar approach is taken to re-defining the categorization of the types of alloys used in antiquity. This offers the possibility of defining 'primary' and 'secondary' alloying practices, the latter which might represent substantial metal recycling. It also leads to speculation about the existence of 'Regional Alloying Practice', which is a way of going from the chemical composition of objects to the minds of the foundry metalworkers who were creating these alloys (e.g. Pollard and Liu 2021). This apporach has been set out in the volume entitled 'Beyond Provenance' (Pollard et al 2018).
Perhaps the most radical work has been to re-think the interpretation of lead isotope data in archaeological metals. Traditionally this has been done using a pair of plots showing all three isotope ratios, based on the plots used in isotope geochemistry to predict the geological age of the deposit. We have extended this to plotting 1/Pb (the inverse of the lead concentration in each object) against one of the lead isotope ratios measured in the same object. This has the advantage of combing chemical and isotopic data in the same diagram, but also allows mixing lines to be highlighted - mixing of different sources of lead, or mixing of copper with lead. More recently we have argued that because archaeology is asking different questions of the data than does isotope geochemistry, then other forms of display can be more useful. For example, in Liu et al (2018) (Beyond ritual bronzes) we experimented with a completyely new means of data presentation, with time as the horizonal axis and one of the isotope ratios as the vertical axis. This allows the easy identification of when lead sources changed, and how many sources were being used at a particular time. This could be as useful as knowing where those sources actually were.
We have spent considerable time looking at the circulation of metal within Bronze Age China (e.g. Liu et al 2018), and also the interaction of the metalworking traditions of the Steppe and Central China (Hsu et al 2016). This latter issue is particularly important in understanding the origins of the Chinese Bronze Age, since it is widely accepted that metalworking arrived in China from the Steppe to the west and the north. This work has included a study of the metalwork from southern Siberia, particularly the Minusinsk basin and Mongolia. Perhaps most signifcantly, we have showed that access to metal resources in Bronze Age China was highly dependent on social status (Liu et al 2020). The 'top elites' had access to highly purified copper, and the alloys were made with a high degree of control. The 'lesser elites' used less pure copper, and the alloying was less precise, suggesting the use of some recycled metal.
In western Asia, the key issue is the origin and spread of alloying copper with tin to produce bronze. This started almost as soon as the smelting of copper (at least 5000 BCE), but there was a major change during the third millennium BCE, both in terms of the metal sources used and the alloying technology, which gave rise to a rapid increase in the ubiquity of bronze. An ongoing focus of this research is the transition from the 'accidental' creation of copper alloys (arising from the smelting of naturally or deliberately mixed ores), to the 'deliberate' addition of alloying metals (principally tin). Attention in Europe has concentrated on the Iberian peninsula, as well as the Atlantic coastal trade. Publications have focussed on the chemical composition of British Bronze Age swords, as opposed to ther objects (daggers and axes), showing strong evidence for different perceptions of the nature and value of each class of object (Bray 2016). In collaboration with Spanish partners, we have attempted to show how large-scale long-term patterns can be mapped during the Iberian Copper Age (Perruchetti et al 2020).
