Work Package A: Main Analytic Work
Work Package A1: Selection and drilled sampling
A detailed compositional analysis of 3,000 silver coins, obtained from drilled samples of the ‘heart metal’ of each coin, will form the methodological basis of this study. To achieve this, 2,800 coins will be selected by the PI in their respective museums. 200 additional coins for drilled sampling (and for further analysis in Work Package B) will be purchased by the PI. Drilled samples will be taken by Dr Matthew Ponting by drilling into the cylindrical edge of the coin using a 0.6mm diameter drill bit, avoiding the surfaces of the coin. The first few millimetres of turnings are discarded as unrepresentative, and then a 12-15 mg drilled sample is taken from a 1 cm deep hole in the coin body. The sampling and analytical strategy of this project ensures that a truly representative bulk chemical composition is established for each coin selected, whilst causing only minimal damage.
Work Package A2: MP-AES and ICP-MS analysis
The samples from the first work package will be analysed using plasma-induced emission spectrometry (MP-AES) by Dr Matthew Ponting. This method is used because of a proven record of providing rigorously reliable data with which to reconstruct patterns of ancient coin manufacture (Butcher and Ponting 2015). The results will provide the proportions of silver, copper, and minor and trace elements for every coin. The same sample solutions will also be used for inductively-coupled plasma mass spectrometry (ICP-MS) allowing the measurement of ultra-trace elements such as platinum, palladium, osmium, indium and iridium. The quality of the data used to understand and interpret the chemistry of silver production, refining and recycling pathways in antiquity is important as some of the distinctions between these pathways can be minimal. The analytical data generated will be examined by a variety of univariate and multivariate statistical techniques to identify compositional groups that can then be related to known numismatic groups and then quantify the levels of difference or similarity between them.
Work Package A3: Lead isotope analysis
Lead isotope analysis will be by thermal ionisation mass spectrometry (TIMS) using the remaining solution from the elemental analysis in the second work package. The work will be subcontracted to the British Geological Survey laboratories under the supervision of Professor Jane Evans and Dr Vanessa Pashley. Not all of the coins sampled will be subjected to lead isotope analysis, given the costs involved, but a selection of 250 samples will be made based on what has been learned from the elemental analyses. The project will develop an innovative approach to the use of lead isotope data together with trace element data, which will allow us to better identify and understand the processes of recycling and mixing, and to identify the likely sources of material that were being mixed together. The second post-doctoral researcher will be tasked with developing detailed data modelling systems for silver alloys using the elemental and isotopic data generated by the project and will publish papers on this methodology and results.
Work Package A4: Microstructure study
The techniques utilised will be Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy (SEM-EDS). The microstructures of the alloys from which ancient coins were made are of crucial importance to their study. Not only can the microstructure inform on the method of manufacture but it is also crucial to understanding the effects of post-depositional corrosion processes. Given that the removal of sections from coins in Museum collections will not be permitted, this project envisages the purchase of selected examples of the main coin types specifically for destructive analyses.
Work Package A5: Metrology
An overview of coin weight standards is important for determining not only the average silver content of the issues and potential relationships of the different coinages to one another, but also the influences of these different coinages on one another. The effects of debasement on the weights of individual surviving specimens can skew the data (due to preferential corrosion and leaching of the copper portion on the alloy from the interior). This will lead to artificially reduced average weights that could potentially give the impression of weight reductions when in fact debasement was occurring instead. The PI has worked on this problem for many years and will utilise and refine innovative strategies for overcoming it. The key starting point is the knowledge of the alloys used that will be generated by this project (Work Package A2) and data about internal leaching of copper derived from the microstructure study and μXES analysis (Work Packages A4 and B2). Data for the weight standards will be derived from weights of surviving specimens that show little sign of wear or corrosion. These will be collected from museum specimens, paper publications and online collections (e.g. coinarchives.com, Coinage of the Roman Republic Online (CRRO) and Online Coins of the Roman Empire (OCRE). Average weights are combined with median and modal values and weight distributions, and adjusted to take account of debasement and internal leaching, to arrive at a likely target weight.
Work Package A6: Hoard data
Money is predominantly a social construct, and to approach its uses the project also has to take into account the evidence for circulation. Most ancient silver coins are found in hoards rather than as single finds. The hoard evidence is important in that it is the only clear evidence we have for patterns of circulation (what coins were probably circulating together, the weight and condition of the older coins at the date of the hoard’s closure). It has been the subject of considerable study, mainly for the light it sheds on the dating of various issues (Crawford 1970, 1974) and their geographical limits of circulation (Crawford 1985; Backendorf 1998). Without a more detailed knowledge of the composition (Work Package A2) combined with metrology (Work Package A5) of the coins, it has proved difficult to say much that is conclusive about the geographical and chronological patterns of hoarding in relation to changes in fineness and weight, particularly for non-Roman type issues of the eastern Mediterranean. The main focus of this project will be on the use of hoards as evidence for public reaction to these changes: whether they were aware of the changes and selected coins for hoarding according to their perceived quality. The third post-doctoral researcher will be engaged to work with the PI on this research.
Work Package A7: Coinage Conference
In the fourth year of the project, as the analytical section of the project draws to a close, the team will hold a two-day international conference on ‘Rome and the Coinages of the Mediterranean’, with invited speakers composed of team members, postdocs, members of our advisory panel and other experts in the field. The conference will be held at the British School at Rome, with which the University of Warwick has strong links. Placing it in Rome will raise the international profile of the project as well as paying homage to the city from which many of the coinages studied originated. The papers arising from the conference would form an edited volume, with editorial work by the PI and the third post-doctoral researcher.