X-ray techniques applied to surface paintings of ceramic pottery pieces from Aguada Culture (Catamarca, Argentina)

摘要

X-ray diffraction (XRD), energy dispersive spectrometry (EDS), x-ray imaging (XRI) and scanning electron microscopy (SEM) techniques were applied to characterize and differentiate surface paintings of archeological pottery from the Aguada Ambato and Portezuelo styles (Catamarca, Argentina). Standard procedures are not always appropriate for such samples (paint layers are porous, nonplanar and discontinue). Image processing is necessary when chemical contrast is not discriminated. Soft x-ray lines (e.g. Fe Q are more revealing because those detected come from shallower depths, clearly depicting the composition of the paint layer. These styles differ in mineralogy and chemistry suggesting that they are two distinctive entities not only on their designs but also on the materials chosen and the technology used. Aguada Portezuelo paints contain Ca (white), Fe-Mn (black), Fe-Mn-Ca (dark reddish) and Fe-Ca (reddish). The white ones correspond to gehlenite, a firing product (possible firing temperature >= 900-1000 degrees C calcite and CaO occur in cases of firing temperatures <900 degrees C. Aguada Ambato presents difficulties for paint discrimination; only EDS spectra show slight differences. White paint from Tricolor Ambato contains mainly Pb-phases (hatchite, anglesite, plumalsite), reddish paint resembles the paste (similar to Fe, hematite); reddish surfaces may have not been painted but polished. Black paint has scarce Mn-minerals. On Black Incised sherds no particular phase was identified suggesting possible organic pigments or resulting from the firing technique. The chemistry and mineralogy of the paste almost always overlap that of the paints; painted layer is irregular and partially worn by years of burial. Copyright (C) 2008 John Wiley & Sons, Ltd.