μ-Raman spectroscopy as a useful tool for improving knowledge of ancient ceramic manufacturing technologies

In recent decades, μ-Raman spectroscopy has become a powerful technique for studying ceramics, with the advantage of performing fast, reproducible and reliable analyses that provide effective information on ceramic technology. In the present paper, the potential of μ-Raman spectroscopy was evaluated by comparing the results of spectroscopic analyses with a wide range of conventional compositional and mineralogical analyses. Particular fragments of pottery from the archaeological site of Pollena Trocchia (Campania, Italy), characterized by a variegated color zonation, a symptom of uncontrolled firing conditions, were subjected to in-depth analytical investigation. Data from the μ-Raman measurements were in very good agreement with the analytical set of conventional analyses and permitted to better constrain the firing temperatures, evaluate changes in the oxidative steps, and assert the provenance of volcanic raw materials. The results illuminated that pottery was crafted by mixing a low-CaO base clay with volcanic temper from the environs of Vesuvius and fired in a not well-controlled firing atmosphere, which determined the development of Fe(III) oxides at rims of sherds and Fe(II)-bearing phases at cores. Moreover, even in the absence of newly-formed minerals, firing temperatures were estimated between 900 and 950 °C, as suggested by the mineralogical and spectroscopic evidence of the prograde 10 Å dehydroxylated phyllosilicates.