ACCURACY IMPROVEMENT BY MEANS OF POROSITY ASSESSMENT AND STANDARDS OPTIMIZATION IN SEM-EDS ELEMENTAL ANALYSES ON ARCHAEOLOGICAL AND HISTORICAL POTTERY AND PORCELAIN

SEM-EDS analyses of pellets produced with powdery clay and ceramic standards and fired at increasing temperatures showed a systematic overestimation of the abundance of heavier detected elements (K, Ca, Ti and Fe) using the conventional procedure of calibration with massive mineral certified materials followed by normalization of the detected values. Errors were particularly noticeable for samples fired in the typical range of temperatures of archaeological and historical pottery (600-900 °C) and for unfired samples, and were attributed to material porosity. An extremely simple method based on the SEM-BSE image analysis is proposed for the semi-quantitative evaluation of porosity. A remarkable increase of accuracy was evidenced when the calibration is performed using a standard with porosity comparable to the samples, with regard to the pottery temperature range.