Analytical Techniques Applied to the Study of Industrial Archaeology Heritage: The Case of Plaiko Zubixe Footbridge

In this work, micro-Raman spectroscopy and micro-energy-dispersive X-ray fluorescence spectroscopy (µ-EDXRF) were applied on microsamples taken from the Plaiko Zubixe footbridge (1927) located in Ondarroa (Basque Country, Spain) in order to investigate the original paint coating and make an evaluation of the conservation state before its restoration. Elemental and molecular images were acquired for the study of the compounds distribution. Some modern pigments such as phthalocyanine blue and green pigments, minium, calcium carbonate, Prussian blue, and hematite were identified. Barium sulfate and titanium dioxide were recognized as opacifier agents. Thanks to the study of the stratigraphies, it has been possible to determine the original paint layer, which includes lead white, ultramarine blue, carbon black, and barium sulfate. In addition, colorimetric analyses made it possible to know the CIELab values of the original layer in order to reproduce the original colour during the planned restoration work. The massive presence of chlorine detected by µ-EDXRF and the corrosion products of the rust layer, in particular akaganeite and hematite, highlighted the atmospheric impact in the conservation of the bridge because they were due to the effect of both marine aerosol and to the presence of acidic components in the environment coming from anthropogenic activity. This work demonstrated the usefulness of a scientific approach for the study of industrial archaeology heritage with the aim to contribute to its conservation and restoration.     

Complexation of CH3Hg+ with chloride,sulfate and carbonate in NaClO4: construction of thermodynamic models

The complexation of CH₃Hg⁺ with major ions present in sea and estuary waters (Cl^?, SO₄^2? and CO₃^2?) was studied potentiometrically in an NaClO₄ medium in the ionic strength range 0.1–3.0 mol dm^?3 at 25 °C. The potentiometric data, treated with non‐linear least squares computer programs, led us to establish the formation of the species CH₃HgCl in equilibrium with chloride, CH₃Hg(SO₄)^? species with sulfate and no complex with carbonate. The stoichiometric stability constants obtained at the different ionic strengths were correlated by means of the modified Bromley methodology (MBM) to determine the corresponding thermodynamic constants and interaction parameters. This study is the second of a series designed to simulate, using the MBM thermodynamic model, the behaviour of methylmercury in different conditions of sea and estuary waters. In the first study of the series, the hydrolysis equilibria of methylmercury in NaClO₄ ionic media were established. Copyright © 2002 John Wiley & Sons, Ltd.     

Complexation and Precipitation of Arsenate and Iron Species in Sodium Perchlorate Solutions at 25∘C

The complexation of As(V) in aqueous solutions in the presence of iron(III) was investigated spectrophotometrically with both variable and constant ionic strengths. The determined thermodynamic and stoichiometric formation constants of the FeHAsO₄⁺ species are log₁₀^∘β = 9.21± 0.01 and log₁₀^Iβ (1.0mol⋅dm⁻³ NaClO₄) = 7.78 ± 0.01, respectively. The numerical treatment of the obtained spectral data was performed with the SPECA program. The analysis required the consideration of the hydrolysis of Fe(III) and the protonation of As(V) in the pH range studied. No significant hydrolysis was observed because of the low pH values (pH < 2.5) involved. The stabilities of the solid Fe(III) arsenates was established by solubility experiments. All of the solubility experiments were performed in aqueous NaClO₄ solutions at constant ionic strength (1.0mol⋅dm⁻³) and at 25^∘C. The experimental data were consistent with FeAsO₄⋅2H₂O being the solid phase (log₁₀ ^∘ K_so = −24.30± 0.08). The corresponding thermodynamic constants were computed by means of the Modified Bromley's Methodology (MBM) that describes the variation of the activity coefficients of all of the ions involved in the complexation and precipitation equilibria with the medium and ionic strength. Finally, the solid phase obtained in this work was also characterized by FT-IR and FT-Raman spectroscopies, and the hydration of the solid iron arsenate was confirmed by X-ray diffraction data.     

Raman fibre optic approach to artwork dating

Raman micro-probe spectroscopy has been applied to the analysis of a non catalogued hand-crafted wallpaper during its restoration process. The analysis has been totally non-destructive without the necessity of taking any sample. The artwork showed a great chromatic palette having been detected the presence of calcium carbonate, Prussian blue, ultramarine blue, gypsum (CaSO4.2H2O), minium (Pb3O4), vermilion (HgS), chrome orange (CaCO3), chrome yellow (PbCrO4), barium sulphate and carbon black (C). From the spectroscopic analysis the date of its manufacturing has been set between 1828 and 1830, introduction of chrome yellow and orange, as well as artificial ultramarine blue, and 1840, when continuous industrial wallpapers were extensively manufactured in Europe.     

On-line FT-Raman and dispersive Raman spectra database of artists’ materials (e-VISART database)

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.