Abstract: The glazed tile decorative art was one of the widely used ornamental techniques for the monumental buildings during the Mughal period, in Pakistan. Coloured tile samples from Jahangir tomb were analyzed to know the glaze composition and to identify the colouring phases used at that time. The study was performed using light microscopy (OM), scanning electron microscopy equipped with energy dispersive X-ray analyzer (SEM-EDS), Raman spectroscopy (RS) and electron microprobe analysis (EMPA). These complementary analytical techniques allowed characterizing the samples as alkali glazes made from plant ashes. The results indicated the use of lead-tin yellow type II for yellow glazes, cobalt and copper for blue glazes, mixtures of yellow and blue glazes for the green glazes, manganese for purple glazes, and a transparent glaze layer for white glazes.
Abstract: Several fungi present high tolerance to toxic metals and some are able to transform metals into metal-oxalate complexes. In this study, the ability of Beauveria bassiana to produce copper oxalates was evaluated in vitro. Growth performance was tested on various copper-containing media. B. bassiana proved highly resistant to copper, tolerating concentrations of up to 20 g.L-1, and precipitating copper oxalates on all media tested. Chromatographic analyses showed that this species produced oxalic acid as sole metal chelator. The production of metal-oxalates can be used in the restoration and conservation of archaeological and modern metal artefacts. The production of copper-oxalates was confirmed directly using metallic pieces (both archaeological and modern). The conversion of corrosion products into copper oxalates was demonstrated as well. In order to assess whether the capability of B. bassiana to produce metal-oxalates could be applied to other metals, iron and silver were tested as well. Iron appears to be directly sequestered in the wall of the fungal hyphae forming oxalates and probably goethite. However, the formation of a homogeneous layer on the object is not yet optimal. Silver nitrate was extracellularly reduced into nanoparticles of elemental silver by an unknown mechanism. The production of copper oxalates is immediately applicable for the conservation of copper-based artefacts. For iron and silver this is not yet the case. However, the vast ability of B. bassiana to transform toxic metals using different immobilization mechanisms seems to offer considerable possibilities for industrial applications, such as the bioremediation of contaminated soils or the green synthesis of chemicals.
Abstract: In the literature, the ability to transform metal compounds into metal oxalates has been reported for different species of fungi. This could be an innovative conservation method for archaeological and artistic metal artefacts. In fact, with a high degree of insolubility and chemical stability even in acid atmospheres (pH 3), metal oxalates provide the surface with good protection. Within the framework of the EU-ARTECH project, different fungal strains have been used to transform existing corrosion patinas on outdoor bronze monuments into copper oxalates, while preserving the physical appearance of these artefacts. Given the promising results obtained with this first attempt, the same approach is now applied within the BAHAMAS (Marie Curie Intra European Fellowship action) project, but extended to other metal substrates, for example iron and silver, which are frequently found in cultural heritage artworks and also encounter several problems of active corrosion. The research is investigating the formation mechanisms and adhesion properties of the newly formed metal oxalates by means of complementary analytical techniques (X-ray diffraction (XRD), FTIR microscopy, Raman microscopy, scanning electron microscopy (SEM-EDS), electrochemical impedance spectroscopy (EIS), colorimetry). For each metal substrate, the most appropriate fungal strain is going to be identified and applied to corroded sheets and the novel fungal treatment compared with those used so far. Treated metal sheets will be monitored during 1-year exposure to different cycles of artificial ageing, to evaluate the corrosion resistance of the fungal patinas obtained. The objective of this contribution is to present the first results achieved so far on naturally corroded bronze sheets during the EU-ARTECH project and the analytical procedure used for the testing of the proposed treatment performances during the BAHAMAS project.
Abstract: Different Fourier transform infrared microspectroscopic techniques, using attenuated total reflection (ATR) mode and single-element mercury–cadmium–telluride (MCT) detector (mapping) or multielement MCT detector (raster scanning), are compared with each other for the characterisation of inorganic compounds and organic substances in paint cross sections. All measurements have been performed on paint cross sections embedded in potassium bromide, a transparent salt in the mid-infrared region, in order to better identify the organic materials without the interference of the usual embedding resin. The limitations and advantages of the different techniques are presented in terms of spatial resolution, data quality and chemical information achieved. For all techniques, the chemical information obtained is found to be nearly identical. However, ATR mapping performed with a recently developed instrumentation shows the best results in terms of spectral quality and spatial resolution. In fact, thin organic layers (∼10 µm) have been not only identified but also accurately located. This paper also highlights the recent introduction of multielement detectors, which may represent a good compromise between mapping and imaging systems.
Abstract: Macro-attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopic imaging is presented as non-destructive analytical methodology with respect to the sample for the study of paint surfaces. This paper illustrates new opportunities offered by a conventional diamond ATR accessory coupled with a focal plane array detector to obtain chemical images of multi-layered paint cross-sections. The use of a large internal reflection element permits to increase the field of view of the imaging area up to 700 Î¼m Ã— 500 Î¼m and to obtain FT-IR images of the complete stratigraphy of the sample. This approach represents a versatile analytical tool to determine the composition of the inorganic and organic painting materials and to obtain information on their distribution within the different layers. In the optical arrangement used, a spatial resolution of approximately 15 Î¼m is achieved without the use of infrared microscope. This study demonstrates the possibilities offered by macro-ATR-FT-IR imaging for a simple identification of the different compounds present in paint cross-sections before performing further molecular and elemental analyses which may be time consuming or require particular sample preparation.
Abstract: Fourier transform infrared (FTIR) spectroscopy is one of the most widely applied techniques for the investigation of cultural heritage materials. FTIR microscopy is well established as an essential tool in the microdestructive analysis of small samples, and the recent introduction of mapping and imaging equipment allows the collection of a large number of FTIR spectra on a surface, providing a distribution map of identified compounds. In this Account, we report recent advances in FTIR spectroscopy and microscopy in our research group. Our laboratory develops, tests, and refines new and less-studied IR spectroscopy and microscopy methods, with the goal of their adoption as routine analytical techniques in conservation laboratories. We discuss (i) the analysis of inorganic materials inactive in the mid-IR region by means of far-IR spectroscopy, (ii) the development of new methods for preparing cross sections, (iii) the characterization and spatial location of thin layers and small particles, and (iv) the evaluation of protective treatments. FTIR spectroscopy and microscopy have been mostly used in the mid-IR region of 4000?600 cm?1. Some inorganic pigments, however, are inactive in this region, so other spectroscopic techniques have been applied, such as Raman spectroscopy. We suggest an alternative: harnessing the far-IR (600?50 cm?1). Our initial results show that far-IR spectroscopy is exceptionally useful with mural paintings or with corrosion products from which larger sample quantities can generally be collected. Moreover, the inorganic composition of a sample can be characterized by the presence of several compounds that are inactive in the mid-IR range (such as sulfides, oxides, and so forth). Stratigraphical analyses by FTIR microscopy can be hindered by the process of cross section preparation, which often involves an embedding organic polymer penetrating the sample?s porous structure. Here, the polymer bands may completely cover the bands of organic compounds in the sample. However, a correct methodological approach can prevent such limitations. For example, it is always advisable to analyze the sample surface before preparing the cross section in order to characterize the preparation layers and the varnish layers, which are generally applied to the surface of a painting both to protect it and improve the color saturation. Furthermore, the innovative use of IR-transparent salts as embedding material for cross sections can prevent contamination of the embedding resin and improve detection of organic substances. Another key point in the use of FTIR microscopy in artwork analysis is spatial resolution. The high-energy output of a new integrated FTIR microscope enhances the ability to characterize and spatially locate small particles and thin layers. Moreover, the new configuration proves extremely useful in the evaluation of protective treatments, because larger areas may be analyzed in less time in comparison to traditional systems, allowing the collection of more statistical data.
Abstract: In the field of FTIR spectroscopy, the far infrared (FIR) spectral region has been so far less investigated than the mid-infrared (MIR), even though it presents great advantages in the characterization of those inorganic compounds, which are inactive in the MIR, such as some art pigments, corrosion products, etc. Furthermore, FIR spectroscopy is complementary to Raman spectroscopy if the fluorescence effects caused by the latter analytical technique are considered. In this paper, ATR in the FIR region is proposed as an alternative method to transmission for the analyses of pigments. This methodology was selected in order to reduce the sample amount needed for analysis, which is a must when examining cultural heritage materials. A selection of pigments have been analyzed in both ATR and transmission mode, and the resulting spectra were compared with each other. To better perform this comparison, an evaluation of the possible effect induced by the thermal treatment needed for the preparation of the polyethylene pellets on the transmission spectra of the samples has been carried out. Therefore, pigments have been analyzed in ATR mode before and after heating them at the same temperature employed for the polyethylene pellet preparation. The results showed that while the heating treatment causes only small changes in the intensity of some bands, the ATR spectra were characterized by differences in both intensity and band shifts towards lower frequencies if compared with those recorded in transmission mode. All pigments' transmission and ATR spectra are presented and discussed, and the ATR method was validated on a real case study.
Abstract: The interaction of pigments and binding media may result in the production of metal soaps on the surface of paintings which modifies their visible appearance and state of conservation. To characterise more fully the metal soaps found on paintings, several historically accurate oil and egg yolk tempera paint reconstructions made with different pigments and naturally aged for 10 years were submitted to attenuated total reflectance Fourier transform infrared (ATR FTIR) microspectroscopic analyses. Standard metal palmitates were synthesised and their ATR spectra recorded in order to help the identification of metal soaps. Among the different lead-based pigments, red lead and litharge seemed to produce a larger amount of carboxylates compared with lead white, Naples yellow and lead tin yellow paints. Oil and egg tempera litharge and red lead paints appeared to be degraded into lead carbonate, a phenomenon which has been observed for the first time. The formation of metal soaps was confirmed on both oil and egg tempera paints based on zinc, manganese and copper and in particular on azurite paints. ATR mapping analyses showed how the areas where copper carboxylates were present coincided with those in which azurite was converted into malachite. Furthermore, the key role played by manganese in the production of metals soaps on burnt and raw sienna and burnt and raw umber paints has been observed for the first time. The formation of copper, lead, manganese, cadmium and zinc metal soaps was also identified on egg tempera paint reconstructions even though, in this case, the overlapping of the spectral region of the amide II band with that of metal carboxylates made their identification difficult. Figure FTIR false colour plot of the azurite distribution on a selected area of the azurite oil paint reconstruction
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