PIXE analysis of jewels from an Achaemenid tomb (IVth century BC)

Ion beam analysis has seldom been applied to gemmology. The privileged location of the Laboratoire de recherche des musées de France, close to some of the most prestigious art collections, along with the implementation of the AGLAE IBA facility, have allowed us to initiate several gemmological research programs since 1991. The latest of these deals with a series of Achaemenid jewels (IVth century BC) exhibited in the Louvre museum. The aim of the present research is three-fold: determination of the coloured materials inlayed in gold, composition of the golden alloys and the inlay fixation technique. Analyses have been carried out by PIXE using an external proton beam under conditions set from test experiments on reference gemstones in order to optimise the experimental parameters. Quantitative chemical analysis of both major and trace elements has allowed us to distinguish between 15 types of fine or ornamental stones as well as man-made materials and to identify a peculiar cement technique. We will describe the analytical procedure in detail, then present the main results obtained on coloured inlays and cement and underline a potential drawback of the technique, i.e. a transient colour variation of the target under the impact of the beam, which needs further investigation.