Evaluation of data processing and analysis approaches for fresco pigment studies by portable X-ray fluorescence spectrometry and portable Raman spectroscopy

Abstract

A portable X-ray fluorescence (XRF) spectrometer and portable Raman spectrophotometer were utilized at the Coriglia, Castel Viscardo excavation site near Orvieto, Italy to study pigments found on fresco. Over eighty fresco samples were analyzed. Identified pigments included vermillion, red ochre, yellow ochre, terre verte, Egyptian blue, and hematite. XRF spectroscopic data were collected utilizing three separate sets of instrument conditions. Various data processing and analysis approaches were evaluated for the XRF and Raman spectroscopic data including scatterplots and analysis of variance on integrated peak areas, live time correction of the XRF spectral intensities, principle components analysis on both the integrated peak areas and spectra, and data fusion of the spectra. Fusion of the high voltage and low voltage under vacuum XRF spectroscopic data provided improved data clustering results over single technique data. Fusion of high voltage XRF spectroscopic data with Raman data also was demonstrated to provide improved differentiation results for certain pigments. Data from individual pigments were then evaluated using these demonstrated best approaches for possible source variations with encouraging results.