In situ DRIFT, Raman, and XRF implementation in a multianalytical methodology to diagnose the impact suffered by built heritage in urban atmospheres

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The Raman spectra of the Na 2 SO 4 -K 2 SO 4 -H 2 O system are not well-defined in the literature. Specifically, the proper identification of sodium and potassium sulphate (aphthitalite or glaserite, K 3 Na(SO 4 ) 2 ) and anhydrous sodium sulphate (thenardite, Na 2 SO 4 ) is particularly problematic because their vibrational profiles present the same main Raman peak at 993 cm −1 and very similar low frequency bands. As proved in bibliography, the similarity of their spectra can often lead to uncertain or erroneous identifications. Considering that aphthitalite and thenardite can be found as degradation products on built heritage materials and the degree of danger associated to them is not the same, being the second one the most harmful, the resolution of this problem has a critical importance. For this reason, in the present work, the Raman spectra of aphthitalite and thenardite are deeply studied to identify the vibrational fingerprints enabling their correct identification. The results here summarized and provided by two different Raman instruments highlight that the spectrum of aphthitalite displays characteristic bands at 1,084 and 1,202 cm −1 . In contrast, the bands at 1,100, 1,129, and 1,152 cm −1 seem to be characteristic of thenardite. Furthermore, when those secondary bands are not observed or mixtures of both compounds are present, the ratio between their most intense bands at 452 and 993 cm −1 is the key for their correct characterization. On the whole, this study fills the gaps observed in literature and gives the solution for the correct identification of aphthitalite and thenardite even when secondary bands are not observed.

Section: Resultsmentioning

confidence: 89%

The Raman spectra of the Na₂SO₄‐K₂SO₄ system: Applicability to soluble salts studies in built heritage

Prieto‐Taboada

Vallejuelo

Veneranda

et al. 2018

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“…A decade ago, for example, a compact, potentially transportable prototype instrument capable of carrying out Raman, laser‐induced breakdown, and laser‐induced fluorescence spectroscopy using a single‐pulsed laser source was developed for the analysis of cultural heritage objects and successfully tested on ultramarine blue pigments and proteinaceous binders . To this seminal body of literature, one must add a handful of Raman studies carried out with the aid of movable instrumentation, which focus on the assessment of certain materials' conservation state or degradation processes, most notably building materials and outdoor steel sculptures . The performances of portable Raman instrumentation have been also compared with those of mobile Fourier‐transform infrared spectroscopy to monitor the conservation treatment of monument plaster surfaces using various classes of polymeric consolidants and protectives …”

Section: Introductionmentioning

confidence: 99%

Evaluation and optimization of the potential of a handheld Raman spectrometer: in situ, noninvasive materials characterization in artworks

Pozzi

Basso

Rizzo

et al. 2019

Decades of technological and methodological advances in Raman spectroscopy have brought this technique from laboratory innovation to a well-established analytical tool with increasing applicability to the study of cultural heritage objects. Enduring research in the field of miniaturization has given rise to new generations of mobile, portable, and handheld spectrometers that have deeply transformed the way in which scientists approach materials analysis. Although sometimes limited in terms of performance and flexibility compared with their benchtop counterparts, miniaturized instruments are typically compact and light, user-friendly, and equipped with fiber optics and batteries, thus

“…In the Pompeii mural paintings, the formation of coquimbite on the surface is generated by the interaction of iron (III) oxide with carbonate and sulfate anions of the plaster generated by cycles of wet deposition of acid aerosol (SO 3 or H 2 SO 4 ) of the environment. As attested by Gomez et al the formation of iron sulfate in the pore stones can occur at pH values lower than 4.5 as occurs in the presence of acid pollutants. Subsequently, coquimbite is produced by hydration processes.…”

Section: Resultsmentioning

confidence: 99%

Darkening of lead‐ and iron‐based pigments on late Gothic Italian wall paintings: Energy dispersive X‐ray fluorescence, μ‐Raman, and powder X‐ray diffraction analyses for diagnosis: Presence of β‐PbO₂(plattnerite) and α‐PbO₂(scrutinyite)

Costantini

Lottici

Bersani

et al. 2020

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This work reports the results of an extensive study carried out on the wall paintings preserved inside the Saint Stephen's chapel in Montani (Val Venosta, Bozen, Italy), by means of μ‐Raman spectroscopy, portable X‐ray fluorescence (XRF) spectrometry, and powder X‐ray diffraction, in order to characterize materials and their alteration products that cause the blackening of paintings. In situ XRF analysis allowed identifying the areas of interest where the blackening appeared. The complementary analytical techniques allowed reconstructing a chromatic palette used by the artists that includes expensive pigments, such as lapis lazuli and cinnabar, indicating a wealthy client. Raman spectra at very low power recorded on blackened degraded samples showed the presence of a mixture of the two polymorphs of lead (IV) dioxide, plattnerite (β‐PbO2), and scrutinyte (α‐PbO2), as degradation products of lead‐based pigments. On these samples, no evidence of white lead was found, although a white lead conversion treatment had been applied on the paintings. The degradation of red lead (Pb3O4) into a mixture of plattnerite, scrutinyte, and anglesite (PbSO4) was demonstrated in some darkened samples. Furthermore, the degradation of haematite (Fe2O3) with the formation of magnetite (Fe3O4) and coquimbite (Fe2(SO4)3·9H2O) was also identified as responsible for the blackening of the paintings. The influence of original materials and environmental and anthropogenic factors such as the valley's orography and the presence of contaminating agents (SOx) is discussed to explain the decay phenomena.