The use of electron spin resonance spectroscopy for determining the provenance of classical marbles

The possibility of identifying the provenance of classical marbles and solv ing related questions, such as the joining fragments problem, via electron spin resonance spectroscopy has been reexamined. The method is based on cha racterization of the Mn2+ impurity ubiquitously present in marbles. Six dif ferent, although correlated, spectroscopic variables, such as intensity, li newidth, metal hyperfine splitting and others have been measured, together with some petrographic properties, for over 500 samples belonging to 14 dif ferent Italian, Greek and Turkish quarrying sites. The work, still in progr ess, is aimed to establish a marble database including all the historically relevant sites within the Mediterranean basin. The experimental data matri x has been analyzed with the aid of multivariate statistical techniques, pr imarily linear and quadratic discriminant analysis, and the ability of the method to classify correctly unknown samples has been estimated through sta ndard techniques (resubstitution, jackknife), but also employing control "u nknown" samples. The essential re suit is that, although the all-variables approach may describe the data set very accurately, the predictive power is due to four variables only, which are a suitable combination of spectrosco pic and petrographic information. In this way 82.4% of the control samples could be assigned correctly whereas inclusion of additional variables in th e classification rule may result in substantially poorer performance. The c onclusion is that ESR spectroscopy, although not providing a complete and g eneral solution for the marble provenance problems, is probably, at the mom ent, the most developed methodology for identifying marbles. Its results, c oupled with artistic historical information, deal correctly with a number o f relevant archaeometric problems.