Degradation process of lead chromate in paintings by Vincent van Gogh studied by means of synchrotron X-ray spectromicroscopy and related methods. 1. Artificially aged model samples

Strong Photochemical Activity of Colored Microplastics Containing Cadmium Pigments: Mechanisms and Implications

Plastics used in daily life are often colored for esthetic and functional purposes. Nevertheless, little is known about the photochemical activity of colored microplastics and the associated risks that are ubiquitous in the environment. In this study, we report the strong photochemical activity of microplastics colored with cadmium pigments. These colored microplastics can be excited by photons within the solar spectrum (<514 nm), readily generating •OH, O2•-, and H2O2. Consequently, they can effectively degrade 17β-estradiol, achieving >91% degradation within 23 h under simulated solar exposure. Among microplastics colored with different cadmium pigments, those with a cadmium pigment S/Se ratio of 2:5 exhibited the highest photoactivity. This is attributed to the narrow band gap, fast charge separation, and efficient charge transfer of the microplastics, as suggested by the energy band, photocurrent, and electrochemical impedance results. Meanwhile, hazardous Cd2+ was leached from colored microplastics mainly owing to the oxidation of pigment lattices by photogenerated holes. Our results reveal that microplastics colored with photoactive inorganic pigments behave drastically differently from uncolored counterparts. This highlights the importance of considering pigments as a critical factor for better assessing the environmental fate and risks of colored microplastics and plastic products.

Effect of low molecular weight organic acids on the lead and chromium release from widely-used lead chromate pigments under sunlight irradiation

Lead chromate pigments are commonly used yellow inorganic pigments. They can pose environmental risks as they contain toxic heavy metals lead and chromium. Low molecular weight organic acids (LMWOAs), as widespread dissolved organic matter (DOM), affect the lead and chromium release from the pigment in water. In this work, the role of LMWOAs in the photodissolution of commercial lead chromate pigment was investigated. The pigment underwent significant photodissolution under simulated sunlight exposure with LMWOAs, and subsequently released Cr(III) and Pb(II). The photodissolution process is caused by the reduction of Cr(VI) by photogenerated electrons of the lead chromate pigment. The LMWOAs promoted photodissolution of the pigment by improving the electron-hole separation. The formation of Cr(III)-contained compounds leads to a slower release of chromium than lead. The photodissolution kinetics increase with decreasing pH and increasing LMWOAs concentration. The photodissolution of lead chromate pigment was basically positively related to the total number of hydroxyl and carboxyl groups in LMWOAs. The LMWOAs with stronger affinity to lead chromate pigment, lower adiabatic ionization potential (AIP) and higher energy of the highest occupied molecular orbital (EHOMO) are favorable to Cr(VI) reduction by photogenerated electrons and pigment photodissolution. 2.39% of chromium and 10.34% of lead released from the lead chromate pigment in natural conditions during a 6-h sunlight exposure. This study revealed the photodissolution mechanism of lead chromate pigment mediated by LMWOAs with different molecular structures, which helps understand the environmental photochemical behavior of the pigment. The present results emphasize the important role of DOM in the heavy metals release from commercial inorganic pigments.

Non-Destructive Analytical Investigation of Decorative Wallpapers Samples of the Nineteenth Century before Their Restoration

In this work, decorative wallpapers (19th century) from an historical palace located in Oiartzun (Basque Country, Spain) were analyzed before their restoration. Micro-energy dispersive X-ray fluorescence spectroscopy, Raman spectroscopy, and attenuated total reflectance infrared spectroscopy were used to investigate the elemental and molecular composition of pigments, the presence of binders, and the state of conservation of the paper support. The aim of the investigation was trying to understand the possible degradation pathways and identify the raw materials in order to choose the best restoration protocol according to the original aspect of wallpapers. As stated from both the elemental distribution and the identification of mineral phases by Raman spectroscopy, the most used pigment was lead chromate. It was mixed with other pigments such as ultramarine blue, zinc chromate, hematite, and atacamite among others to obtain different shades and they were applied mixed with an animal glue. Brass, identified thanks to elemental micro-EDXRF maps, was employed as a shiny decorative element. In addition, a partial degradation of cellulose was detected due to its natural ageing, the acidic nature of lignin, and to a phenomenon of humidity of the walls. Probably the deposition of black particulate matter was the cause of the darkening of the painting surfaces.

Evaluating Cr behaviour in two different polluted soils: Mechanisms and implications for soil functionality

This work investigates the mechanisms determining Cr speciation and availability in two different soils polluted with two chromium sources (an industrial sludge, highly polluted with Cr, and Cr(VI) solution) and the influence of these parameters on the recovery of the soil functions related with biological quality and plant growth. The experiment was carried out in greenhouse conditions using 36 pots of 17 kg for the growth of Silene vulgaris for 21 months. Logistic Regression Model using Lasso estimator shows that soil organic matter (SOM) and pH control Cr availability in studied soils. In soils treated with the sludge, X ray Absorption spectroscopy showed that Cr was present as Cr(III), biological quality indicators increased and plants were able to grow. However, in soils polluted with Cr(VI), Cr availability was significantly different in the two soils. In the alkaline and poor in organic matter soil, 12% of Cr(VI) remained in the soil leading to the decrease of soil quality indicators and the total inhibition of plant growth. In the neutral soil, Cr(VI) was totally reduced to Cr(III) by soil organic matter (SOM), quality indicators were not affected and plants grown properly. Infrared Spectroscopy showed that different functional groups reacted with Cr in the two soils. This study highlights the importance to understand the mechanisms underlaying Cr redox and adsorption reactions in Cr polluted soils as they determine the potential recovery of the functions related with biological quality indicators and plant growth. The methodology proposed allows this study in complex soil samples at realistic concentrations and may be useful for risk assessment and for the planning of managing strategies in Cr polluted soils.

Damages Induced by Synchrotron Radiation-Based X-ray Microanalysis in Chrome Yellow Paints and Related Cr-Compounds: Assessment, Quantification, and Mitigation Strategies

Synchrotron radiation (SR)-based X-ray methods are powerful analytical tools for several purposes. They are widely used to probe the degradation mechanisms of inorganic artists' pigments in paintings, including chrome yellows (PbCr_1-xS_xO₄; 0 ≤ x ≤ 0.8), a class of compounds often found in Van Gogh masterpieces. However, the high intensity and brightness of SR beams raise important issues regarding the potential damage inflicted on the analyzed samples. A thorough knowledge of the SR X-ray sensitivity of each class of pigment in the painting matrix is therefore required to find analytical strategies that seek to minimize the damage for preserving the integrity of the analyzed samples and to avoid data misinterpretation. Here, we employ a combination of Cr K-edge X-ray absorption near-edge structure spectroscopy, Cr-K_β X-ray emission spectroscopy, and X-ray diffraction to monitor and quantify the effects of SR X-rays on the stability of chrome yellows and related Cr compounds and to define mitigation strategies. We found that the SR X-ray beam exposure induces changes in the oxidation state and local coordination environment of Cr ions and leads to a loss of the compound's crystalline structure. The extent of X-ray damage depends on some intrinsic properties of the samples (chemical composition of the pigment and the presence/absence and nature of the binder). It can be minimized by optimizing the overall fluence/dose released to the samples and by working in vacuum and under cryogenic conditions.

Quantifying solvent action in oil paint using portable laser speckle imaging

The exposure of oil paintings to organic solvents for varnish removal or to water for the removal of surface dirt can affect the chemical and physical properties of oil paint in an undesired way. Solvents can temporarily plasticise and swell the polymerised oil paint binding medium, enhancing both the thermal mobility and mechanical displacement of pigments embedded in this film. The enhancement of these microscopic motions can affect both the chemical and physical stability of the object as a whole. In order to minimise solvent exposure during cleaning, an analytical method that can quantitatively measure the microscopic motions induced by solvent uptake, is required first. In this study, we use Fourier Transform Laser Speckle Imaging (FT-LSI) and a newly developed portable FT-LSI setup as highly resolved motion detection instruments. We employ FT-LSI to probe pigment motion, with high spatiotemporal resolution, as a proxy for the destabilising effects of cleaning solvents. In this way, we can study solvent diffusion and evaporation rates and the total solvent retention time. In addition, qualitative spatial information on the spreading and homogeneity of the applied solvent is obtained. We study mobility in paint films caused by air humidity, spreading of solvents as a result of several cleaning methods and the protective capabilities of varnish. Our results show that FT-LSI is a powerful technique for the study of solvent penetration during oil paint cleaning and has a high potential for future use in the conservation studio.

Oxygen K-edge X-ray Absorption Spectra

We review oxygen K-edge X-ray absorption spectra of both molecules and solids. We start with an overview of the main experimental aspects of oxygen K-edge X-ray absorption measurements including X-ray sources, monochromators, and detection schemes. Many recent oxygen K-edge studies combine X-ray absorption with time and spatially resolved measurements and/or operando conditions. The main theoretical and conceptual approximations for the simulation of oxygen K-edges are discussed in the Theory section. We subsequently discuss oxygen atoms and ions, binary molecules, water, and larger molecules containing oxygen, including biomolecular systems. The largest part of the review deals with the experimental results for solid oxides, starting from s- and p-electron oxides. Examples of theoretical simulations for these oxides are introduced in order to show how accurate a DFT description can be in the case of s and p electron overlap. We discuss the general analysis of the 3d transition metal oxides including discussions of the crystal field effect and the effects and trends in oxidation state and covalency. In addition to the general concepts, we give a systematic overview of the oxygen K-edges element by element, for the s-, p-, d-, and f-electron systems.

Pigment darkening as case study of In-Air Plasma-Induced Luminescence

We introduce the use of an In-Air Plasma-Induced Luminescence (In-Air-PIL) spectroscopy as an alternative to classical chemical and crystallographic methods used in materials science. The In-Air-PIL is evaluated on a case study investigating the effect of light aging on the darkening of five pristine yellow pigments commonly used in artworks. We show that the darkening is not associated to changes in the chemical composition, but to a loss in crystallinity, indicating an amorphization process of the pigments induced and catalyzed by the light irradiation. This favors the interaction of the pigment molecules with oxygen and carbon adsorbed from the environment or solved in the binding agent, subsequently leading to the formation of oxalates and carbonates as observed in other works. We demonstrate that the In-Air-PIL results are in perfect agreement with more complex classical materials science analysis methods, making our plasma-driven method a potentially easier and faster technique.

Sunlight-Mediated Lead and Chromium Release from Commercial Lead Chromate Pigments in Aqueous Phase

Lead chromate pigments are included in a group of the most widely used pigments, which account for 3% of worldwide lead consumption. This study reports the photoactivity of commercial lead chromate pigment (i.e., chrome yellow) under simulated sunlight. It underwent photodissolution in the presence of organic acid and dissolved organic matter in the aqueous phase, releasing Pb(II) and Cr(III). Pb(II) was released more readily than Cr(III) which mainly formed hydroxides and oxides. The photodissolution can be activated by light with a wavelength <514 nm. The reaction is mediated by the reduction of Cr(VI) in the pigment by self-generated electrons. The kinetics were mainly affected by the electron-hole separation efficiency which can be enhanced by electron donors. The reaction rate decreases with increasing solution pH as the photodissolution process consumes protons. The photodissolution of the chrome yellow pigment was further confirmed in a river water sample under natural sunlight, with 11.28% of lead and 2.56% of chromium released in 7 h. This study highlights the importance of considering photochemical processes in risk assessments and regulations of commercial semiconductor pigments, which are currently based on their solubility.

Characterization of Cr (VI) - Containing solid phase particles in dry dust deposition in Daejeon, South Korea

Solid phase speciation of chromium in dry dust deposition and road paint was determined using transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS). Spherical black carbon aggregates in dry dust deposition contained discrete nano-sized lead chromate (PbCrO₄) and zinc chromate (ZnCrO₄), which likely originated from yellow traffic paint and zinc chromate primer (corrosion resistant pigment), respectively based on their main applications. Road marking paint samples from auto roads included lead chromate particles whose size, shape, composition and crystal structure were similar to those in dry dust deposition. A slight difference was found at the particle boundary. Namely, lead chromate in traffic paint was encapsulated by silica-bearing matrix, while discrete lead chromate in the black carbon of dry deposition was rarely enclosed within silica-bearing matrix. The Cr K edge X-ray absorption near edge structure (XANES) spectrum for dry deposition showed the characteristic pre-edge resonance peak similar to the spectra for the Cr(VI) standard and road paint, but the lower intensity. The amount of Cr(VI) accounted for approximately 45% of the total Cr in the dust sample. The solid phase speciation of Cr observed using TEM and their valence states determined using XANES were consistent with the chemical speciation determined using the sequential extraction. The contribution of this study is that XANES was applied to identify Cr valance states in urban dust deposition and zinc chromate was found as a Cr(VI) phase in dry dust deposition using TEM. These study results provide novel data on Cr speciation and Cr(VI)-containing mineral phases in dry dust deposition and their potential sources. Based on the wide use of lead and zinc chromate, atmospheric contamination with these solid phase speciation of Cr(VI) is expected in other cities in the world.

Photochemistry of Artists' Dyes and Pigments: Towards Better Understanding and Prevention of Colour Change in Works of Art

The absorption of light gives a pigment its colour and its reason for being, but it also creates excited states, that is, new molecules with an energy excess that can be dissipated through degradation pathways. Photodegradation processes provoke long-term, cumulative and irreversible colour changes (fading, darkening, blanching) of which the prediction and prevention are challenging tasks. Of all the environmental risks that affect heritage materials, light exposure is the only one that cannot be controlled without any impact on the optimal display of the exhibit. Light-induced alterations are not only associated with the pigment itself but also with its interactions with support/binder and, in turn, are further complicated by the nature of the environmental conditions. In this Minireview we investigate how chemistry, encompassing multi-scale analytical investigations of works of art, computational modelling and physical and chemical studies contributes to improve our prediction of artwork appearance before degradation and to establish effective preventive conservation strategies.

Time-Resolved Photoluminescence Microscopy for the Analysis of Semiconductor-Based Paint Layers

In conservation, science semiconductors occur as the constituent matter of the so-called semiconductor pigments, produced following the Industrial Revolution and extensively used by modern painters. With recent research highlighting the occurrence of various degradation phenomena in semiconductor paints, it is clear that their detection by conventional optical fluorescence imaging and microscopy is limited by the complexity of historical painting materials. Here, we illustrate and prove the capabilities of time-resolved photoluminescence (TRPL) microscopy, equipped with both spectral and lifetime sensitivity at timescales ranging from nanoseconds to hundreds of microseconds, for the analysis of cross-sections of paint layers made of luminescent semiconductor pigments. The method is sensitive to heterogeneities within micro-samples and provides valuable information for the interpretation of the nature of the emissions in samples. A case study is presented on micro samples from a painting by Henri Matisse and serves to demonstrate how TRPL can be used to identify the semiconductor pigments zinc white and cadmium yellow, and to inform future investigations of the degradation of a cadmium yellow paint.

The effects of hydraulic retention time (HRT) on chromium(VI) reduction using autotrophic cultivation of Chlorella vulgaris

Chromium is an acutely toxic heavy metal that is known to be a carcinogen. Of the two predominant forms of chromium, Cr(III) and Cr(VI), Cr(III) has only about one thousandth the toxicity of Cr(VI). Using microalgal biomass is one way to remove Cr(VI) from the environment. Four days of hydraulic retention time (HRT) was required to completely reduce 10 mg/L of Cr(VI) in the influent. Microalgal biomass is conventionally regarded as an adsorbent in most Cr(VI) reduction studies. However, this study found that Chlorella vulgaris had the potential to convert Cr(VI) to Cr(III) through the enzymatic route of chromium reductase although the measured chromium reductase activity of C. vulgaris was less than that reported values obtained in bacteria. X-ray absorption near-edge spectroscopy (XANES) analysis further showed the absorption edge of Cr(III) in Cr(VI)-treated C. vulgaris, supporting the assumption of Cr(VI) potentially being converted to less-toxic Cr(III).

Analyzing the Heterogeneous Hierarchy of Cultural Heritage Materials: Analytical Imaging

Objects of cultural heritage significance are created using a wide variety of materials, or mixtures of materials, and often exhibit heterogeneity on multiple length scales. The effective study of these complex constructions thus requires the use of a suite of complementary analytical technologies. Moreover, because of the importance and irreplaceability of most cultural heritage objects, researchers favor analytical techniques that can be employed noninvasively, i.e., without having to remove any material for analysis. As such, analytical imaging has emerged as an important approach for the study of cultural heritage. Imaging technologies commonly employed, from the macroscale through the micro- to nanoscale, are discussed with respect to how the information obtained helps us understand artists' materials and methods, the cultures in which the objects were created, how the objects may have changed over time, and importantly, how we may develop strategies for their preservation.

"Paintings Fade Like Flowers": Pigment Analysis and Digital Reconstruction of a Faded Pink Lake Pigment in Vincent van Gogh's Undergrowth with Two Figures

Color fading in Vincent van Gogh's Undergrowth with Two Figures was studied chemically to facilitate the creation of a digital reconstruction of fugitive colors . The painting contains a field of white, green, orange, and yellow flowers under a canopy of poplar trees with two central figures-a man and a woman, arms entwined. From Van Gogh's letters, however, it is known that he painted the picture with some pink flowers, which appear to have altered, presumably to white. Raman spectroscopy was applied to microsamples of paint to identify the faded pigment as geranium lake, which in this painting consists of the dye, eosin (2',4',5',7'-tetrabromofluorescein). For the first time, lead(II) sulfate has been specifically identified as the likely inorganic substrate for a geranium lake used by Van Gogh in the last months of his life. Microfocus X-ray fluorescence (MXRF) spectroscopy was subsequently used in situ to analyze the white flowers to identify bromine as a proxy for eosin, thus indicating an original pink coloration. Of the 387 white flowers analyzed, 37.7% contained measurable bromine and were, therefore, originally pink. Several cross-sections from these formerly pink areas were assessed using a combination of visual inspection and microcolorimetry to create a colored mask in Adobe Photoshop to digitally reconstruct a suggestion of the original appearance of the painting with regard to the faded flowers. Additionally, microfadeometry was undertaken for the first time on a painting cross-section sample to understand the actual fading kinetics of the underlying bright pink geranium lake used by Van Gogh. A combination of Raman microspectroscopy, MXRF, and scanning electron microscopy energy dispersive spectroscopy (SEM-EDS) were utilized in situ and on paint microsamples to identify the complete palette used to create Undergrowth with Two Figures.

Handheld new technology Raman and portable FT-IR spectrometers as complementary tools for the in situ identification of organic materials in modern art

A non-invasive approach has been carried out to characterize painting materials used in modern artworks conserved in the art collection of Carandente's museum at Palazzo Collicola in Spoleto (Italy). This work is focused on the cross-validation of the handheld BRAVO Raman spectrometer, that uses a sequentially Shifted Excitation (SSE) to mitigate fluorescence, for the characterization specifically of organic materials. The analytical procedure, combining XRF, Raman and reflection infrared spectroscopy, allowed a complete characterization of the artists' palettes; particularly eight different synthetic dyes belonging to the class of pigment red (PR) and pigment yellow (PY.), synthetic and traditional binders, such as alkyd resin and lipids have been easily identified.

Non-Invasive and Non-Destructive Examination of Artistic Pigments, Paints, and Paintings by Means of X-Ray Methods

Recent studies are concisely reviewed, in which X-ray beams of (sub)micrometre to millimetre dimensions have been used for non-destructive analysis and characterization of pigments, minute paint samples, and/or entire paintings from the seventeenth to the early twentieth century painters. The overview presented encompasses the use of laboratory and synchrotron radiation-based instrumentation and deals with the use of several variants of X-ray fluorescence (XRF) as a method of elemental analysis and imaging, as well as with the combined use of X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Microscopic XRF is a variant of the method that is well suited to visualize the elemental distribution of key elements, mostly metals, present in paint multi-layers, on the length scale from 1 to 100 μm inside micro-samples taken from paintings. In the context of the characterization of artists' pigments subjected to natural degradation, the use of methods limited to elemental analysis or imaging usually is not sufficient to elucidate the chemical transformations that have taken place. However, at synchrotron facilities, combinations of μ-XRF with related methods such as μ-XAS and μ-XRD have proven themselves to be very suitable for such studies. Their use is often combined with microscopic Fourier transform infra-red spectroscopy and/or Raman microscopy since these methods deliver complementary information of high molecular specificity at more or less the same length scale as the X-ray microprobe techniques. Since microscopic investigation of a relatively limited number of minute paint samples, taken from a given work of art, may not yield representative information about the entire artefact, several methods for macroscopic, non-invasive imaging have recently been developed. Those based on XRF scanning and full-field hyperspectral imaging appear very promising; some recent published results are discussed.

Ab initio study of PbCr(1-x)S x O4 solid solution: an inside look at Van Gogh Yellow degradation

Van Gogh Yellow refers to a family of lead chromate pigments widely used in the 19th century and often mixed with lead sulfate to obtain different yellow hues. Unfortunately, some paintings, such as the famous Sunflowers series, suffered degradation problems due to photoactivated darkening of once bright yellow areas, especially when irradiated with UV light. Recent advanced spectroscopic analyses have proved that this process occurs mostly where the pigment presents a sulfur-rich orthorhombic phase of a PbCr(1-x)S x O4 solid solution, while chromium-rich monoclinic phases are lightfast. However, the question of whether degradation is purely a surface phenomenon or if the bulk properties of sulfur-rich pigments trigger the process is still open. Here, we use first-principles calculations to unveil the role of sulfur in determining important bulk features such as structure, stability, and optical properties. From our findings, we suggest that degradation occurs via an initial local segregation of lead sulfate that absorbs at UV light wavelengths and provides the necessary energy for subsequent reduction of chromate ions into the greenish chromic oxide detected in experiments. In perspective, our results set reliable scientific foundations for further studies on surface browning phenomena and can help to chose the best strategy for the proper conservation of art masterpieces.

Investigation on the hazing of a Brazilian contemporary painting

A whitish crystalline-like coating was observed on the surface of the painting "Incêndio", 1990, produced by Emmanuel Nassar and awarded at the 6th Biennial of Cuenca. This work belongs to the Contemporary Art Museum of the University of São Paulo (MAC-USP) and such coating modified the artwork characteristics, causing an unpleasant effect and compromising its exhibition. The choice of the proper conservation and restoration strategies involves the understanding of the degradation process, demanding the identification of the chemical compounds formed on the painting surface, as well as of the other components in the painting. The results here obtained from Raman and optical microscopies, FTIR-ATR, SEM-EDS and GC-MS, revealed that the efflorescence chemical composition is almost only palmitic acid, with minor contents of stearic acid and their methyl esters, and that the paints are composed by chrome yellow, amorphous carbon and toluidine red pigment; an aluminum silicate filler in the black paint applied on the aluminum ground was also detected. Hierarchical Cluster Analyses (HCA) of the Raman spectra also revealed that the concentration of the efflorescence minor components depends on the paint composition. It was suggested, therefore, that the degradation process resulted from segregation and migration of mainly palmitic acid from the dried paints. Restoration methodologies used in similar cases, as well as factors that contribute to this process, were discussed.

The efficiency of micro-Raman spectroscopy in the analysis of complicated mixtures in modern paints: Munch's and Kupka's paintings under study

Twenty one mock-up samples containing inorganic pigments primarily used at the turn of the 19th and 20th century were selected for comparative study and measured by micro-Raman and portable Raman spectrometers. They included pure grounds (chalk-based, earth-based and lithopone-based), grounds covered by resin-based varnish, and different paint layers containing mixtures of white, yellow, orange, red, green, blue and black pigments, usually in combination with white pigments (titanium, zinc and barium whites or chalk). In addition, ten micro-samples obtained from seven paintings of two world-famous modern painters Edvard Munch and František Kupka have been investigated. Infrared reflection spectroscopy (FTIR), portable X-ray fluorescence (XRF) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) were used as supplementary methods. The measurements showed that blue pigments (ultramarine, Prussian blue and azurite), vermilion and ivory black in mixture with whites provided characteristic Raman spectra, while Co-, Cd- and Cr- pigments' bands were suppressed by fluorescence. The best success rate of micro-Raman spectroscopy has been achieved using the 780 nm excitation, however, the sensitivity of this excitation laser in a portable Raman instrument significantly decreased. The analyses of micro-samples of paintings by E. Munch and F. Kupka showed that micro-Raman spectroscopy identified pigments which would remain unidentified if analyzed only by SEM-EDS (zinc yellow, Prussian blue). On the other hand, chromium oxide green and ultramarine were not detected together in a sample due to overlap of their main bands. In those cases, it is always necessary to complement Raman analysis with other analytical methods.

Structural and electronic properties of the PbCrO4 chrome yellow pigment and of its light sensitive sulfate-substituted compounds

Chrome Yellows (CY) are a family of synthetic pigments of formula (PbCr_(1−x)S_xO₄) used by van Gogh. We investigate structure/property relations in CY by first-principles methods, providing insight into their possible degradation mechanisms.

Metal concentrations and distribution in paint waste generated during bridge rehabilitation in New York State

Between 1950 and 1980, lead and chromium along with other metals have been used in paint coatings to protect bridges from corrosion. In New York State with 4500 bridges in 11 Regions 2385 of the bridges have been rehabilitated and subsequently repainted after 1989 when commercial use of lead based paint was prohibited. The purpose of this research was to address the concentration and distribution of trace metals in the paint waste generated during bridge rehabilitation. Using hypothesis testing and stratified sampling theory, a representative sample size of 24 bridges from across the state was selected that resulted in 117 paint waste samples. Field portable X-ray fluorescence (FP-XRF) analysis revealed metal concentrations ranged from 5 to 168,090 mg kg(-1) for Pb, 49,367 to 799,210 mg kg(-1) for Fe, and 27 to 425,510 mg kg(-1) for Zn. Eighty percent of the samples exhibited lead concentrations greater than 5000 mg kg(-1). The elevated iron concentrations may be attributed to the application of steel grit as an abrasive blasting material routinely used by state Departments of Transportation in the paint removal process. Other metals including Ba and Cr were observed in the paint waste as well. As a result of the paint formulation, metals were found to be associated in the paint waste (Pb correlated with Cr (r=0.85)). The elevated metal concentrations observed raises concern over the potential impact of leaching from this waste stream.

Toxic effects of Mn2O3 nanoparticles on rat testis and sex hormone

BACKGROUND AND OBJECTIVE

The safety of Mn2O3 nanoparticles (which are extensively used in industries) on male reproductive system is not known. Hence, we investigated the effects of Mn2O3 nanoparticles on male reproductive system.

MATERIALS AND METHODS

A total of 40 Wistar adult male rats were randomly assigned to four groups of 10 rats each. Three groups received Mn2O3 solution in concentrations of 100, 200, and 400 ppm orally for 14 days; the control group received equal volume of saline solution. Blood samples and testicles were collected for analysis.

RESULTS

Significant reduction in luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone, spermatogonial cells, primary spermatocyte, spermatid and Leydig cell was observed in the Mn2O3 nanoparticles treated groups compared with controls.

CONCLUSION

Mn2O3 nanoparticles significantly reduce FSH, LH, and testosterone levels resulting in a significant reduction in testicular cytology.

Electrospray ionization linear trap quadrupole Orbitrap in analysis of old tempera paintings: application to nineteenth-century Orthodox icons

Proteomic approach in combination with mass spectrometry demonstrates a great potential for identification of proteinaceous materials in works of art. In this study we used a linear trap quadrupole Orbitrap (LTQ-Orbitrap), a state-of-the-art mass spectrometer for parts per million accuracy analyses of peptides behind tryptic hydrolysis. After the efficiency of the proteomic method was confirmed for reference and model samples, micro-samples from historical paintings were for the first time analysed using this technique. Superior performances of the liquid chromatography-mass spectrometry approach using a LTQ-Orbitrap mass spectrometer allowed identification of egg yolk peptides in two samples from nineteenth-century Orthodox icons, indicating egg tempera as the painting technique. Accurate precursor ion masses, in the range of ±2 ppm, and retention times of tryptic peptides strengthen protein identification. Additionally, in all historical samples the presence of animal glues suggested that the ground layer was likely bound using bovine collagen. Comparing to results acquired using matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry in our previous study, here we achieved higher ion scores and protein scores, better sequence coverage and more identified proteins. In fact, a combination of the two mass spectrometric techniques provided overlapping and complementary data, related to the detection of peptides with different physicochemical properties.

Optimal sample preparation to characterize corrosion in historical photographs with analytical TEM

An alternative focused ion beam preparation method is used for sampling historical photographs containing metallic nanoparticles in a polymer matrix. We use the preparation steps of classical ultra-microtomy with an alternative final sectioning with a focused ion beam. Transmission electron microscopy techniques show that the lamella has a uniform thickness, which is an important factor for analytical transmission electron microscopy. Furthermore, the method maintains the spatial distribution of nanoparticles in the soft matrix. The results are compared with traditional preparation techniques such as ultra-microtomy and classical focused ion beam milling.

Nanoscale investigation of the degradation mechanism of a historical chrome yellow paint by quantitative electron energy loss spectroscopy mapping of chromium species

Getting the picture: The investigation of 100 year old chrome yellow paint by transmission electron microscopy and spectroscopy has led to the identification of four types of core-shell particles. This nanoscale investigation has allowed a mechanism to be proposed for the darkening of some bright yellow colors in Van Gogh's paintings (e.g. in Falling leaves (Les Alyscamps), 1888).

SR-FTIR imaging of the altered cadmium sulfide yellow paints in Henri Matisse's Le Bonheur de vivre (1905-6)--examination of visually distinct degradation regions

SR-FTIR imaging has been used to map the mid-IR active photo-degradation phases in two thin sections of cadmium yellow paint removed from Henri Matisse's Le Bonheur de vivre (1905-1906, The Barnes Foundation). These samples represent both the darkened cadmium yellow foliage in the upper left of the work and the lightened cadmium yellow field beneath the central reclining figures. The altered cadmium yellow paints from both regions were found to contain cadmium carbonate (CdCO3), cadmium sulphate (CdSO4), and cadmium oxalate (CdC2O4). Each of these phases was imaged to determine their positions as a function of depth, with the aim of better understanding the role of each phase in the degradation mechanism. This speciation mapping is critical because cadmium oxalate was used in this period as an additive in cadmium yellow light. In addition, cadmium carbonate and cadmium sulphate were synthesis starting materials for cadmium yellow, and so their distribution throughout the paint layer can provide an indication of their roles. It was established that cadmium oxalate is localized at the surface of the paint layer, cadmium carbonate is found deeper in the layer but still enriched at the surface, and cadmium sulphate is distributed throughout the layer. This distribution, along with the chloride content of the paint suggesting a cadmium chloride starting material, is consistent with an alteration mechanism in which the cadmium sulphide is oxidized to sulphate and this is then converted to carbonate and oxalate. The relative solubilities of the three photo-degradation products are also relevant to their locations in the paint film.

The use of synchrotron radiation for the characterization of artists' pigments and paintings

We review methods and recent studies in which macroscopic to (sub)microscopic X-ray beams were used for nondestructive analysis and characterization of pigments, paint microsamples, and/or entire paintings. We discuss the use of portable laboratory- and synchrotron-based instrumentation and describe several variants of X-ray fluorescence (XRF) analysis used for elemental analysis and imaging and combined with X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Macroscopic and microscopic (μ-)XRF variants of this method are suitable for visualizing the elemental distribution of key elements in paint multilayers. Technical innovations such as multielement, large-area XRF detectors have enabled such developments. The use of methods limited to elemental analysis or imaging usually is not sufficient to elucidate the chemical transformations that take place during natural pigment alteration processes. However, synchrotron-based combinations of μ-XRF, μ-XAS, and μ-XRD are suitable for such studies.

Collagen-based proteinaceous binder-pigment interaction study under UV ageing conditions by MALDI-TOF-MS and principal component analysis

This study focuses on acquiring information on the degradation process of proteinaceous binders due to ultra violet (UV) radiation and possible interactions owing to the presence of historical mineral pigments. With this aim, three different paint model samples were prepared according to medieval recipes, using rabbit glue as proteinaceus binders. One of these model samples contained only the binder, and the other two were prepared by mixing each of the pigments (cinnabar or azurite) with the binder (glue tempera model samples). The model samples were studied by applying Principal Component Analysis (PCA) to their mass spectra obtained with Matrix-Assisted Laser Desorption/Ionization-Time of Flight Mass Spectrometry (MALDI-TOF-MS). The complementary use of Fourier Transform Infrared Spectroscopy to study conformational changes of secondary structure of the proteinaceous binder is also proposed. Ageing effects on the model samples after up to 3000 h of UV irradiation were periodically analyzed by the proposed approach. PCA on MS data proved capable of identifying significant changes in the model samples, and the results suggested different aging behavior based on the pigment present. This research represents the first attempt to use this approach (PCA on MALDI-TOF-MS data) in the field of Cultural Heritage and demonstrates the potential benefits in the study of proteinaceous artistic materials for purposes of conservation and restoration.