Confocal XANES and the Attic black glaze: the three-stage firing process through modern reproduction

The decorated black- and red-figured Athenian vases (sixth and fifth century BC) and the plain black-glazed ware represent a milestone in our material culture due to their aesthetic and technological value; the Attic black glaze is of particular interest since it is a highly resistant potash-alumino-silicate glass, colored by magnetite nanocrystals (<200 nm). This study presents a new methodological approach for correlating the iron oxidation state in the black glaze layer with the manufacturing process by means of conventional and confocal X-ray absorption near edge spectroscopy (XANES). The enhanced surface sensitivity of confocal XANES is combined with conventional XANES resulting in higher counting rates to reliably evaluate the iron oxidation state (Fe(3+)/ΣFe) of the surface layer. A detailed description of the new evaluation procedure is presented. The three-stage firing process was retraced by correlating selected attic black-glazed (BG) specimens from different periods (Archaic, Classical, Hellenistic) with laboratory reproductions. The modern BG specimens serving as reference samples were produced by following the three-stage firing process (i.e., under oxidizing-reducing-oxidizing (ORO) conditions) at different top temperatures, using clay suspensions of different particle size produced with treatment of raw illitic clays from Attica.