Statistical evaluation of data obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES) for archaeological copper ingots

Abstract

ICP-AES was used for the quantitative determination of copper and copper accompanying elements (As, Ag, Bi, Co, Fe, Mn, Ni, Pb, Sb, Sn, Zn) that are present as impurities in plano-convex ingots from seven late bronze age hoards in Slovenia. Principal component analysis (PCA) was used for multi-dimensional data evaluation and for visualisation of ingots as points in reduced two-dimensional space. From the analytical and PCA results, it has been concluded that iron as well as arsenic, and to a less extent nickel and antimony, are the most relevant variables for differentiation between ingots. Furthermore, on the basis of PCA results, the relationship between object position in two-dimensional space and its elemental composition has been established. The information obtained by PCA transformation allowed us to make some hypotheses about the possible multi-stage smelting process and about ore types used in ancient copper production. We also show that, in general, there are no significant differences among the copper ingots from different Slovenian locations.