Paint Relics on Middle Age Building Stones as Proxies of Commercial Routes and Artistic Exchanges: A Multi-Analytical Investigation

Abstract

Fifty-four pieces out of 356 marble pieces deriving from the decorative and architectonic apparatus of the medieval monastic complex of S. Francesco of Castelletto (Genoa, Italy) preserve traces of varicolored paint layers. Microscopic samples of green, blue, red, pink, white, and yellow paint relics were collected by scalpel and analyzed by means of Scanning Electron Microscope coupled with Energy Dispersive Spectroscopy (SEM-EDS), µ-Raman, and Fourier Transform Infra-Red Spectroscopy with Attenuated Total Reflection (FTIR-ATR), to characterize pigments and binders. The combined results from the different techniques allowed verification that stone decoration in Genoa during the Middle Ages encompassed a calcite groundwork and the use of a mixture of oils and proteins (probably egg) to apply pigments. The assemblage of impurities within the pigment has been correlated with the provenance sites along the commercial continental (Hungary and France) and maritime (Sardinia, Cyprus, or Veneto) routes between the 13th and 15th centuries. Moreover, the investigation of the painted layer improved the characterization of the decorative techniques in use in Genoa during the Middle Ages.

Antimony and Nickel Impurities in Blue and Green Copper Pigments

“…As frequent, they classified goethite, malachite, hematite, and cuprite; and as less frequent-cerussite, cinnabar, quartz, calcite, rutile and anatase, rhodochrosite, carbon, beudantite, and jarosite. Barite was also reported as an admixture in azurite layers [36,63], or azurite transformed to atacamite mixed with paratacamite layers [12]. Raman spectroscopy confirmed barium carbonate in azurite [64].…”

“…The impurities of copper pigments most reported in the literature are red and brown iron oxides and hydroxides-hematite and goethite [12,33,34,61]. Identification of individual grains of malachite in azurite paint layers is also common [18,36,62,63]. Aru et al [33] extended the list and divided the impurities identified in azurite specimens into two groups.…”

Methodological Approach to Reconstructing Lost Monuments from Archaeological Findings: The San Francesco di Castelletto Church in Genoa

“…Pigments collected from diverse Middle Age pieces were analysed in situ by optical microscopy, collecting data on size and relative distribution of pigment particles in the pictorial layer. The study was deepened by means of SEM-EDS analysis [11]. Microanalysis evidenced that blue areas correspond to copper carbonate (Figure 6A,B).…”

“…The yellow pigment is a lead-based product (Figure 6G,H). Subsequent µ-Raman (Horiba Jobin-Yvon Explora_Plus) and FT-IR spectroscopy (Spectrum 65 FT-IR spectrometer with a diamond attenuated total reflectance (ATR) device) analysis confirmed azurite as the main component of blue paint layers, red ochre for the various shades of red, green earths for green areas, and massicot for yellow traces [11]. Scrivano et al [11] analysed in detail the paint relics, aiming at reconstructing the Middle Age art supply market and paint techniques.…”

“…The marble is homeoblastic, organised in a granoblastic texture, with low-grade anisotropy and linear to lobate grain boundaries. (C) Comparison between maximum grain size (MGS) values of the white marbles most diffused in ancient times (graph modified from Antonelli and Lazzarini[11]). The red dotted line presents the mean MGS value of the sample from the present study, and the red area corresponds to the Gaussian curve of the measured MGS values.…”