Sandwich structures in the Etruscan-Padan type pottery.

The sandwich (black core) structure in the production of Etruscan-Padan type pottery was investigated. Petrographic, X-ray diffraction (XRD) and Mössbauer data showed that colour changes from core to margin are related to differences in both Fe oxidation state and abundance of maghemite, hercynite and hematite. The occurrence of maghemite and hercynite and the higher quantity of Fe(II) in the cores suggest poor oxygen diffusion in the potsherds during firing. This is congruent with the occurrence of high fractions of paramagnetic Fe in octahedral sites, located in the amorphous phase probably derived from chlorite breakdown, and with the wide range of grain-size distribution of oxidic particles, indicated by the slowing down of superparamagnetic relaxation as temperatures are lowered.