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Accuracy improvement by means of porosity assessment and standards optimization in SEM-EDS and XRF elemental analyses on archaeological and historical pottery and porcelain

Turco, F., Davit, P., Cossio, R., Agostino, A., Operti, L.
Journal of archaeological science: Reports 2017 v.12 pp. 54-65
X-ray fluorescence spectroscopy, archaeology, calcium, calibration, ceramics, clay, energy-dispersive X-ray analysis, glass, image analysis, iron, minerals, pellets, porosity, potassium, scanning electron microscopy, temperature
SEM-EDS and XRF 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/glass 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, especially for SEM-EDS, was evidenced when the calibration is performed using a standard with porosity comparable to the samples, with regard to the pottery temperature range. Conversely, for the analysis of high-fired samples simulating porcelain (1200°C) no substantial difference was observed with respect to the usual massive minerals/glass calibration. Finally, results showed the unsuitability of calibration performed by means of unfired pellets, for both pottery and porcelains.