A Non-Invasive and Sustainable Characterization of Pigments in Wall Paintings: A Library of Apulian Colors

Abstract

This paper proposed a multianalytical, non-invasive, accessible and expensive (compared to traditional ones) approach for the characterization of pictorial surfaces. A set of 18 pigments and 37 mixtures widely used in the Middle Ages in the Apulia (Italy) artistic and archaeological contexts was considered, and corresponding replicas were produced. Pigments were first characterized by X-ray powder diffraction (XRPD), then replicas were studied by optical microscopy using a portable instrument, colorimetry and fiber optic reflectance spectroscopy (FORS). The investigation provided encouraging results, which allowed the creation of a library including diagnostic microscopic, colorimetric and reflectance markers of each pigment and the identification of the mixtures’ components.

On Devotional Artworks: A Non-Invasive Characterization of Pigments of the Madonna della Croce Wall Painting in Triggiano (Bari, Southern Italy)

“…The red colour of the background was due to the finer fraction of the red pigment, which was invisible to the microscope magnification (lower than 220×). The parameters observed on both pigments would seem to be consistent with red ochre [24,29,33,34] and vine black (C) [29,35] markers, respectively. The most common red ochres used as pigment in the wall paintings are those composed of earth deposits rich in Fe(III) oxides, and the main chromophore is hematite (Fe 2 O 3 ) [34].…”

“…For the microscopic characterization of samples, the observation of peculiar markers proposed by Fioretti et al [29] was followed. It considered the chromatic, morphological, optical, and other features of pigment particles and their relationship with the background.…”

“…The observation by the portable digital microscope allowed us to evaluate the parameters observed as key markers by Fioretti et al [29] for all 42 samples and to suppose the nature of pigments on the basis of comparison with their data. Thanks to these observations, samples with similar characteristics were grouped.…”

“…For the characterization of pigments in surface pictorial layers, in addition to the most common investigation techniques, including Raman spectroscopy and X-ray fluorescence spectroscopy, the current literature also provides numerous examples of the effectiveness of fibre optic reflectance spectroscopy [19][20][21][22][23], colorimetry [24][25][26] and portable digital microscopy [27][28][29].…”

“…An efficient approach based on the matching of results obtained by means of portable microscopy, FORS, and colorimetry for the identification of pigments and their mixtures in wall painting was proposed by Fioretti et al [29]. This multianalytical approach, which also provides a detailed library of results and photomicrographs, was considered for the analysis of pictorial material in the Madonna della Croce painting, and the obtained results were compared with XRF data.…”