Tracing impurities to minerals: overlapping XRF and XRD data sets derived from synchrotron techniques

Recipes for the manufacture of metals-based synthetic minerals, as well as the pharmacological preparations they formed an integral part of, are historically well documented in the Greco-Roman world. The purpose of the present research is to identify and evaluate these preparations in archaeological artifacts (labelled ‘cosmetics’ or ‘medicines’, found as pellets or mineralised powders in small ceramic/metal containers) to match ‘recipe’ with ‘product’. To that end, we have applied synchrotron techniques, specifically the spatial overlay of 2D XRF (major/trace elements) over XRD scans (crystalline phases), to two lead-based powders recovered from within metal vials from the ‘tomb of the doctor’ cemetery of Alykes, Pydna in Macedonia, Greece (4thc BCE). The aim is to ascribe major elements and impurities to spatially well-defined crystalline phases. While the major element (i.e., Pb) clearly overlaps with the main Pb-rich phases identified (i.e., cerussite and hydrocerussite), minor/trace elements (for example Cu, Fe, Mn) equally clearly distribute themselves in a number of non-Pb based phases (i.e., quartz or amorphous). Had these elements been part of burial contamination they would likely ‘blanket’ cover all phases indiscriminately. Fe can be in the form of amorphous ferrihydroxides, on which Cu adsorbs; it can adhere onto quartz. When no quartz is present, organics (waxes/resins) may be the ‘carriers’ of these elements. We argue that being able to differentiate between elements arising from burial environment (randomly on all phases observed) versus those integrally associated with the preparation of the powder is a powerful tool in the study of these unique samples of early pharmaceuticals technology.