Analysis of bulk and inorganic degradation products of stones, mortars and wall paintings by portable Raman microprobe spectroscopy
Analytical Chemistry, Universidad del País Vasco / Euskal Herriko Unibertsitatea, Leioa, Basque Country, SpainAnalytical and Bioanalytical Chemistry (Impact Factor: 3.44). 06/2004; 379(1):42-50. DOI: 10.1007/s00216-004-2496-2
This work reports the use of a portable Raman microprobe spectrometer for the analysis of bulk and decaying compounds in carbonaceous materials such as stones, mortars and wall paintings. The analysed stones include limestone, dolomite and carbonaceous sandstone, gypsum and calcium oxalate, both mono- and dihydrated, being the main inorganic degradation products detected. Mortars include bulk phases with pure gypsum, calcite and mixtures of both or with sand, soluble salts being the most important degradation products. The pigments detected in several wall paintings include Prussian blue, iron oxide red, iron oxide yellow, vermilion, carbon black and lead white. Three different decaying processes have been characterised in the mortars of the wall paintings: (a) a massive absorption of nitrates that reacted with calcium carbonate and promoted the unbinding of pigment grains, (b) the formation of black crusts in the vault of the presbytery and (c) the thermodecomposition of pigments due to a fire.
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- "The results suggest that chromatic change in the paint layer can be due to the presence of calcium oxalates. Several studies have reported the occurrence of weddellite in degraded areas of mural paintings (Pérez-Alonso et al., 2004;Nevin et al., 2008;Sarmiento et al., 2008) due to the metabolic activity of the microorganisms, which secrete oxalic acid that reacts with calcium compounds present on the surface (Sarmiento et al., 2008).3.2.2. Analysis of the oxalates in simulated assays The influence of microorganisms metabolic activity on the malachite pigments alteration was studied using high cells density of pure and mixed cultures e microsamples removed from degraded areas of the painting which retain the presence of total microbial communities, and simulating the influence of these cultures on real sterilised microsamples, as mentioned in the section of methods. "
ABSTRACT: Oxalate film formation is a pathology that often occurs in mural paintings and may result from the concomitant action of microorganisms and environmental conditions. Low Choir of the Convent of Nossa Senhora do Saudacao (Portugal) has mural paintings with an extraordinary beauty, which over time have been suffered polychromy degradation and biofilm formation, presenting an ideal case study to investigate the role and impact of microorganisms in the biodeterioration process. Bacterial populations, filamentous fungi belonging to the genera Cladosporium, Penicillium, Nectria and yeast strain of the genera Rhodotorula were isolated from these wall paintings. The penetration of fungal hyphae in the microstructure of mortars, observed by scanning electron microscopy, seems to be responsible for cracking and detachments in some areas of the painting. The study revealed that the veils on the surface of the paintings are essentially oxalates and that these biofilms are caused by metabolic activity of bacterial communities. Furthermore, the colour alteration of green areas due to microorganisms was detected by Raman microscopy, in real samples and under in vitro conditions, being the result of the metabolic activity of microorganisms present on the paintings, which promote calcium oxalates formation over the malachite paint layers.
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ABSTRACT: Raman spectroscopy with portable fiber optics microprobe, FT-IR spectroscopy and ion chromatography have been applied to the study of mortars and wall paintings in the church of Santa Marı́a de Hermo (Asturias, North of Spain) before the restoration works. This scientific analysis was performed to compare with a diagnosis report based on restorer’s expertise. The church showed problems of damp as well as clear evidences of flora, fungus and mould presence. The combination of both vibrational spectroscopic techniques made it possible to determine the chromatic palette of the wall paintings composed of: CaCO3, carbon black, red ochre, yellow ochre, minium and cinnabar. In addition, some decay products have been determined, such as nitrate salts, and gypsum.From the conclusions of the scientific analysis the supposedly distemper wall paintings from the XVIIth century were confirmed as frescoes and were then dated back to the XVth century by the art historians. The detachment of the pigment grains from the wall paintings is attributed to the loss of the binding power of CaCO3 by its partial transformation into calcium nitrate due to chemical reactions with nitrates. Clear evidence of nitrate migration from the graveyard behind the northern wall of the church has been determined from the quantification of nitrate salts by ion chromatography.
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ABSTRACT: Raman spectroscopy has been widely applied in the analysis of different types of artwork. This technique is sensitive, reliable, non-destructive and can be used in situ. However, there are few references in the literature regarding specific Raman spectra libraries for the field of artwork analysis. In this paper, the development of two on-line databases with Fourier transform Raman (FT-Raman; 1064 nm) and dispersive Raman (785 nm) spectra of materials used in fine art is presented; both are implemented in the e-vibrational spectroscopic databases of artists' materials database (e-VISART). The database provides not only spectra, but also information about each pigment. It must be highlighted that for each pigment or material several spectra are available from different dealers. Some of the FT-Raman spectra available in the e-VISART database have not been published until now. Some examples in which the e-VISART database has been successfully used are presented.
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