1,721,031 research outputs found
Identificazione non invasiva e proprietà fotofisiche di pigmenti a base di cadmioutilizzati nella pittura moderna e contemporanea
No full textDegradation process of lead chromate in paintings by Vincent van Gogh studied by STEM-EELS
No full textOptical coherence tomography and reflection FTIR as complementary tools for examination of varnish layers in Vincent van Gogh’s Sunflowers– preliminary results
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XAFS and species-specific imaging: new and old combinations for elucidating natural alteration reactions in pigmented materials
No full textNon-invasive Investigations of Paintings by Portable Instrumentation: The MOLAB Experience
No full textThe in situ non invasive methods have experienced a significant development in the last decade because they meet specific needs of analytical chemistry in the field of cultural heritage where artworks are rarely moved from their locations, sampling is rarely permitted, and analytes are a wide range of inorganic, organic and organometallic substances in complex and precious matrices. MOLAB, a unique collection of integrated mobile instruments, has greatly contributed to demonstrate that it is now possible to obtain satisfactory results in the study of a variety of heritage objects without sampling or moving them to a laboratory. The current chapter describes an account of these results with particular attention to ancient, modern, and contemporary paintings. Several non-invasive methods by portable equipment, including XRF, mid- and near-FTIR, UV–Vis and Raman spectroscopy, as well as XRD, are discussed in detail along with their impact on our understanding of painting materials and execution techniques. Examples of successful applications are given, both for point analyses and hyperspectral imaging approaches. Lines for future perspectives are finally drawn
Non-invasive identification of metal oxalates and carboxylates on paintings by reflection mid-FTIR spectroscopy
No full textNon-invasive identification of metal-oxalate complexes on polychrome artwork surfaces by reflection mid-infrared spectroscopy
No full textIn this work a reflection mid-infrared spectroscopy study of twelve metal-oxalate complexes, of interest in art conservation science as alteration compounds, was performed. Spectra of the reference materials highlighted the presence of derivative-like and/or inverted features for the fundamental vibrational modes as result of the main contribution from the surface component of the reflected light. In order to provide insights in the interpretation of theses spectral distortions, reflection spectra were compared with conventional transmission ones. The Kramers-Kronig (KK) algorithm, employed to correct for the surface reflection distortions, worked properly only for the derivative-like bands. Therefore, to pay attention to the use of this algorithm when interpreting the reflection spectra is recommended. The outcome of this investigation was exploited to discriminate among different oxalates on thirteen polychrome art-works analyzed in situ by reflection mid-infrared spectroscopy. The visualization of the v(s)(CO) modes (1400-1200 cm(-1)) and low wavenumber bands (below 900 cm(-1)) in the raw reflection profiles allowed Ca, Cu and Zn oxalates to be identified. Further information about the speciation of different hydration forms of calcium oxalates were obtained by using the KK transform. The work proves reflection mid-infrared spectroscopy to be a reliable and sensitive spectro-analytical method for identifying and mapping different metal-oxalate alteration compounds on the surface of artworks, thus providing conservation scientists with a non-invasive tool to obtain information on the state of conservation and causes of alteration of artworks
Chromium speciation methods and infrared spectroscopy for studying the chemical reactivity of lead chromate-based pigments in oil medium
No full textEnvironmental factors, such as light, humidity and temperature are triggering agents for the alteration of organic and/or inorganic constituents of oil paintings. The oxidation of the organic material is favored by increasing of relative humidity and temperature, whereas processes involving changes of the oxidation states of a number of inorganic pigments (e.g., vermilion, cadmium yellows, zinc yellows, chrome yellows) are mainly activated by light-exposure. In view of the optimization of the long-term conservation and restoration strategies of paintings it is of relevant interest to establish the consequences of thermal parameters (temperature and relative humidity) on the chemical/photochemical-reactivity and the nature of the alteration products of light sensitive-pigments in oil medium.To this aim here we propose a multi-method analytical approach based on the combination of diffuse reflectance UV–Vis, FTIR, synchrotron radiation (SR)-based micro X-ray fluorescence (μ-XRF)/micro-X-ray absorption near edge structure (XANES) and electron paramagnetic resonance (EPR) spectroscopies for studying the effects of different relative humidity conditions before and after light exposure on the reactivity of a series of lead chromate-based pigments [such as PbCrO∙ PbO (monoclinic), PbCrO (monoclinic) and PbCrSO (orthorhombic)] in an oil medium. The investigation of paint models was also compared to that of a late 19th century historical orthorhombic PbCrSO oil paint.Diffuse reflectance UV–Vis and FTIR spectroscopies were used to obtain information associated with chromatic changes and the formation of organo-metal degradation products at the paint surface. SR-based Cr K-edge μ-XANES/μ-XRF mapping analysis and EPR spectroscopy were employed in a complementary fashion to determine the amount, nature and distribution of Cr(III) and Cr(V)-based alteration compounds within the paints with micrometric spatial resolution.Under the employed thermal aging conditions, lead(II)-carboxylates and reduced Cr-compounds (in abundance of up to about 35% at the surface) have been identified in the lead chromate-based paints. The tendency of chromates to become reduced increased with increasing moisture levels and was favored for the orthorhombic PbCrSO compounds. The redox process gave rise to the formation of Cr(V)-species in relative amount much higher than that was formed in the equivalent paint which was exposed only to light. After light-exposure of the thermally aged paints, compounds ascribable to the oxidation of the organic binder were detected for all the types of pigments. Nevertheless, the previous thermal treatment increased the tendency toward photo-reduction of only the PbCrSO pigment. For this light-sensitive compound, the thickness variation of the reduced Cr-rich (ca. 70%) photo-alteration layer with moisture levels could be ascribed to a surface passivation phenomenon that had already occurred before photochemical aging
Photo-induced redox reactions of Cr, Cd and Hg: a significant threat to modern and ancient works of art
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