Analytical Study of a Chromatic Deterioration: Lead Pigments Fading in 18th Century Mural Paintings by SEM-EDS, µ-XRD and µ-RAMAN

Abstract

Analysis on 18th century mural paintings were carried out, both in situ and in laboratory, in order to identify the causes of a dramatic chromatic alteration of flesh tones. Many of the figures of the 18 mural scenes covering the nave vault of the Church of Santa Clara in Sabugueiro (Southern Portugal) have turned black while others have punctually bleached (Figure). The first assumption was the degradation of white lead pigment in an alkaline environment (fresco technique). The analytical setup comprised in-situ spectro-colorimetry, complemented with optic (OM) and electronic scanning microscopy (SEM-EDS), micro X-ray diffraction (µ-XRD), µ-Raman and Fourier transform infrared micro spectroscopy (µ-FTIR).