Cadmium Pigments Research Articles

Modern Muralists in the Spotlight: Technical and Material Characteristics of the 1946–1949 Mural Paintings by Almada Negreiros in Lisbon (Part1)

This paper presents the first insight into how Almada Negreiros, a key artist of the first generation of modernism in Portugal, created his mural painting masterpiece in the maritime station of Rocha do Conde de Óbidos in Lisbon. This set of six monumental mural paintings dates from 1946 to 1949 and is considered Almada’s artistic epitome. As part of the ALMADA project: Unveiling the mural painting art of Almada Negreiros, the murals are being analyzed from a technical and material perspective to understand his modus operandi and the material used. This is the first study of this nature carried out on site and in the laboratory using standard and more advanced imaging, non-invasive analysis, and microanalysis techniques. This article reports the results obtained with visual examination, technical photography in visible (Vis), visible raking (Vis-Rak), complemented by 2D and 3D optical microscopy (OM), scanning electron microscopy with energy-dispersive spectrometry (SEM-EDS), and Fourier transform infrared micro-spectroscopy (µ-FTIR) of the paint layers. The results show the similarities, differences, and technical difficulties that the painter may have had when working on the first, third, and presumably last mural to be painted. Vis-Rak light images were particularly useful in providing a clear idea of how the work progressed from top to bottom through large sections of plaster made with lime mortars. It also revealed an innovative pounced technique used by Almada Negreiros to transfer the drawings in full scale to the walls. Other technical characteristics highlighted by the analytical setup are the use of textured, opaque, and transparent paint layers. The structure of the paintings does not follow a rigid build-up from light to dark, showing that the artist freely adapted according to the motif represented. As far as the colour palette is concerned, Almada masterfully uses primary and complementary colours made with Fe-based pigments and with synthetic ultramarine blue, cadmium pigments, and emerald green.

Cadmium Yellow Pigments in Oil Paintings: Optical Degradation Studies Utilizing 3D Fluorescence Mapping Supported by Raman Spectroscopy and Colorimetry

The degradation of cadmium yellow in paintings is influenced by various factors, primarily environmental conditions and light exposure. Applying a thin protective layer of linseed oil on the surface could help mitigate these processes. Linseed oil, being a natural material, acts as a barrier against harmful atmospheric agents like moisture and oxygen, which contribute to the degradation of pigments including cadmium yellow. Additionally, linseed oil reduces direct light exposure, thereby lowering the risk of fading and color alteration. In this study, we explored the degradation of cadmium pigments mixed with oil and applied on canvas. We elucidated how the use of a binder prevents the direct oxidation of the pigment, inducing artificial degradation by irradiating samples with UVA (365 nm) and UVC (250 nm) sources. By employing various spectroscopic techniques such as three-dimensional fluorescence mapping (PLE) and Raman, along with colorimetric analysis, we gained a comprehensive understanding of the degradation process, particularly when linseed oil serves as a protective layer.

Impacts of dissolved organic matter on the aggregation and photo-dissolution of cadmium pigment nanoparticles in aquatic systems

Cadmium pigments are a group of inorganic pigments used in consumer products. The aggregation behavior and photo-dissolution process of cadmium pigment nanoparticles in aquatic systems control their environmental fate, which is largely unknown. Herein, we investigated the influence of dissolved organic matter (DOM) on the aggregation behavior and photo-dissolution process of CdS nanoparticles in aquatic systems. Bare CdS nanoparticles are prone to aggregation in both NaCl and CaCl2 solutions. DOM can remarkably increase the colloidal stability of CdS nanoparticles owing to the steric hindrance and enhanced electrostatic repulsion. With 10 mg/L Suwannee River natural organic matter (SRNOM), the colloidal stability of CdS nanoparticles is significantly enhanced in NaCl solutions (i.e., the critical coagulation concentration, CCCNa, is 707.2 mM). Suwannee River humic acid (SRHA) has a stronger stabilization effect than SRNOM due to its higher molecular weight and aromaticity. The Ca2+ cations can induce charge neutralization and structural compacting of DOM corona, efficiently reducing the colloidal stability of CdS nanoparticles. The CCCCa is 10.8 mM and 14.9 mM with 10 mg/L SRNOM and SRHA, respectively. Upon solar irradiation, the presence of a low concentration of SRNOM (3 mg/L) can enhance the photo-dissolution of CdS nanoparticles and the consequent Cd2+ leaching. This is caused by the facilitated electron transfer from CdS nanoparticles to O2 induced by SRNOM corona, leading to better electron-hole separation. However, a high concentration of SRNOM inhibited the photo-dissolution of CdS nanoparticles due to the strong inner filter effect and the scavenging of phototransients. The colloidal stability of SRNOM-coated CdS nanoparticles increases in NaCl but decreases in CaCl2 solutions after irradiation owing to the oxidation of SRNOM corona. Our results highlight the decisive role of DOM in the environmental fate of cadmium pigments.

Properties of poly (vinyl chloride) membranes containing cadmium pigments, irradiated with UV radiation

The cadmium pigments were yellow, orange and red pigments. They consisted of cadmium sulphide and cadmium sulphide with zinc sulphide as well as cadmium sulphide with cadmium selenide. Their quantitative composition and specific surface area were examined. The pigments were used to color the poly (vinyl chloride) plastisol films, which were then exposed to UV radiation. The surfaces of the coloured membranes were examined by infrared spectroscopy before and after irradiation with UV. The changes occurred in the PVC membrane were investigated by thermogravimetric analysis. The degree of crystallinity of the pigments and the membrane was determined by X-ray diffraction. The color change of the membranes was determined from the spectra obtained by reflection spectroscopy, and the components of colour L*, a* and b* were calculated. Base of them, the tolerance of colour deviations (ΔE*) was determined. The calculations allowed for the determination of the effect of UV irradiation on the change of the colour of the membranes and confirmation of the degradation of the pigments and polymer membrane.

Cadmium sulfide / selenide pigments

AbstractCadmium sulfide and selenide pigments (cadmium pigments) belong to the inorganic yellow, orange and red pigments. Cadmium sulfide pigments are based on the wurtzite lattice, where cadmium can be partially substituted by zinc or mercury and sulfide by selenide. Cadmium pigments are characterized by excellent optical and application characteristics in particular regarding brightness of shade, hiding power, tinting strength, and weather fastness. The declining use of cadmium-containing materials in the last decades is a result of the environmental discussion and the development of less problematic substitute products, especially of bismuth vanadate and high-value organic, temperature-stable yellow and red pigments.

Sunlight mediated cadmium release from colored microplastics containing cadmium pigment in aqueous phase

The plastics industry is the biggest consumer of cadmium pigments. Little is known about the leaching of hazardous Cd2+ from colored microplastics containing cadmium pigment in aquatic systems. Here, we reported the release of Cd2+ from different sized microplastics containing cadmium pigment in aqueous phase under simulated sunlight. The release of Cd2+ was caused by the photo-dissolution of cadmium pigment. The release kinetics is highly size-dependent. It was relatively low for microplastics with size larger than 0.85 mm but increased significantly with decreasing size for microplastics smaller than 0.85 mm. The polymer matrix was oxidized during light exposure, leading to lower average molecular weight and the formation of oxygen-containing groups. Part of the polymer matrix was degraded into soluble organic carbon under simulated sunlight, resulting in continuous Cd2+ release from the pigment particles embedded in the polymer. The polymer degradation rate is also highly size-dependent. The degradation of the polymer matrix and the release of Cd2+ were intertwined. Cadmium leaching from microplastics from a commercial product containing cadmium pigment was confirmed in water under simulated sunlight. This work suggests that the photochemical processes of inorganic pigments will lead to the release of heavy metals from colored plastic debris.

Cadmium and its inorganic compounds - expressed as Cd - inhalable fraction. Documentation of proposed values of occupational exposure limits (OELs)

Cadmium (Cd) is a white metal with a bluish tint. It forms a number of compounds occurring in them on the degree of oxidation 2+. Cadmium compounds are water-soluble to varying degrees. The highest risk groups include employees involved in the production of nickel-cadmium batteries, alloys, cadmium pigments as well as employees of non-ferrous metal smelters and cutting welders of metals covered with a cadmium anti-corrosion layer. According to the Central Register of Data on Exposure to Substances , Preparations, Factors or Technological Processes on Carcinogenic or Mutagenic Action, 4276 workers in Poland were exposed to cadmium and its compounds. Cadmium is absorbed into the body through inhalation and digestive systems. In humans, the absorption is 2–50% and 4–6%, respectively. Elimination of cadmium from the body is a slow process. The estimated half-life of cadmium is from 5 to 30 years. Results of studies conducted in subjects exposed to cadmium in the work environment showed that the threshold concentration of cadmium in urine, at which increased excretion of low molecular weight proteins in urine was found, is 5–10 µg/g creatinine. In 1993, IARC identified cadmium and its compounds as a human carcinogen (group 1). The results of experimental studies in rats provided evidence of cadmium carcinogenicity as a result of inhalation exposure. Cadmium is recognized by SCOEL as a category C carcinogen, i.e. as a genotoxic carcinogen for which a threshold of action (concentration) can be determined, also called a practical threshold. The critical organs for the toxic effects of cadmium and its inorganic compounds in humans, depending on the route of exposure, are kidneys, lungs and possibly bones. The critical effect of cadmium on kidneys is increased excretion of low molecular weight proteins in urine, while the critical effect on lungs is the carcinogenic effect. Inhalation studies in rats exposed to cadmium at concentrations of 30 µgCd/m3, 13.4 µgCd/m3 and 10 µgCd/m3 for 18 months were used as the basis to propose TLV-TWA. The concentration of 10 µg Cd/m3 was taken as the NOAEL value. After applying the formula and taking into account the uncertainty factors with a total value of 10, the concentration of 0.001 mg/m3 (1 µgCd/m3) was determined as the TLV-TWA value for the inhaled fraction. Biological monitoring is the best indicator of cadmium exposure. The excretion of cadmium in urine enables the assessment of cumulative cadmium in the body and takes into account all sources of cadmium exposure, including contaminated food and smoking, while the blood cadmium concentration is a measure of current exposure. Previous BEI values in blood and urine were 5 μgCd/l and 5 μgCd/g creatinine, respectively. After discussion at the 91st meeting of the Interministerial Committee for TLVs and PELs, these values were maintained as mandatory. This article discusses the problems of occupational safety and health, which are covered by health sciences and environmental engineering.

Time-Resolved Photoluminescence Microscopy Combined with X-ray Analyses and Raman Spectroscopy Sheds Light on the Imperfect Synthesis of Historical Cadmium Pigments.

Recent studies have shown that modern pigments produced after the Second Industrial Revolution are complex systems characterized by a high level of heterogeneities. Therefore, it is fundamental to adopt a multianalytical approach and highly sensitive methods to characterize the impurities present within pigments. In this work we propose time-resolved and spectrally resolved photoluminescence (PL) microscopy for the mapping of luminescent crystal defects and impurities in historical cadmium-based pigments. PL analysis is complemented by X-ray diffraction, X-ray fluorescenceand Raman spectroscopies, andbyscanning electron microscopy to determine the chemical composition and crystal structure of samples. The study highlights the heterogeneous and complex nature of historical samples that can be associated with the imperfect manufacturing processes tested during the period between the 1850s and 1950s. The results also allow us to speculate on a range of synthesis processes. Since it is recognized that the stability of paints can be related to pigments synthesis, this research paves the way to a wider study on the relationship between synthesis methods and deterioration of cadmium pigments and paints. This rapid and immediate approach using PL can be applied to other semiconductor pigments and real case studies.

Sunlight Promotes Fast Release of Hazardous Cadmium from Widely-Used Commercial Cadmium Pigment.

Cadmium pigments are widely used in the polymer and ceramic industry. Their potential environmental risk is under debate, being the major barrier for appropriate regulation. We show that 83.0 ± 0.2% of hazardous cadmium ion (Cd2+) was released from the commercial cadmium sulfoselenide pigment (i.e., cadmium red) in aqueous suspension within 24 h under simulated sunlit conditions. This photodissolution process also generated sub-20 nm pigment nanoparticles. Cd2+ release is attributed to the reactions between photogenerated holes and the pigment lattices. The photodissolution process can be activated by both ultraviolet and visible light in the solar spectrum. Irradiation under alkaline conditions or in the presence of phosphate and carbonate species resulted in reduced charge carrier energy or the formation of insoluble and photostable cadmium precipitates on pigment surfaces, mitigating photodissolution. Tannic acid inhibited the photodissolution process by light screening and scavenging photogenerated holes. The fast release of Cd2+ from the pigment was further confirmed in river water under natural sunlight, with 38.6 ± 0.1% of the cadmium released within 4 h. Overall, this study underscores the importance to account for photochemical effects to inform risk assessments and regulations of cadmium pigments which are currently based on their low solubility.

Infrared Spectra of U.S. Automobile Original Finishes (1998–2000).IX. Identification of Bismuth Oxychloride and Silver/White Mica Pearlescent Pigments Using Extended RangeFT‐IRSpectroscopy,XRFSpectrometry, andSEM/EDSAnalysis

Bismuth oxychloride (BiOCl) was the first viable synthetic pearl pigment developed 50years ago. It was only used for a limited time period in automotive paint (model years 1998-2000), serving to produce luster for a single Chrysler black metallic color. Identification of this pigment in an unknown automotive paint can thus facilitate determination of the vehicle of origin. Bismuth oxychloride imparts effects similar to those produced by silver/white mica pearlescent pigments, and such a pigment was used together with bismuth oxychloride in at least one original equipment manufacturer (OEM) basecoat. Silver/white micas are now used primarily in white pearl tricoat systems. This article describes the identification of bismuth oxychloride and silver/white mica pearlescent pigments in automotive finishes using FT-IR spectroscopy, X-ray fluorescence (XRF) spectrometry, and SEM/EDS analysis. Data for some cadmium pigments, which were used in automotive paint several decades ago, are also presented as they produce infrared absorptions similar to that of bismuth oxychloride.

Analysis of cadmium-based pigments with time-resolved photoluminescence

For the first time the kinetic emission properties of commercially available cadmium-based pigments were studied. For analysis, a streak camera-based photoluminescence device was used with a temporal resolution ranging from ps to μs, considering the emission from both the band edge and the first deep trap state. Band edge emission shows a rapid picosecond lifetime strictly related to pigment composition, with cadmium sulphide pigments decaying more rapidly than those based on cadmium sulphoselenides. The trap state emission lifetime is on the order of tens of microseconds and is uncorrelated with pigment composition. In addition, a high dependence of spectral and lifetime emission properties on excitation irradiance has been observed, as carrier recombination in cadmium pigments is highly influenced by electron trapping. All this information provides insight into the photo-physical properties of these widely employed modern pigments, which highlights how luminescence measurements are useful for discriminating among cadmium pigments.

Properties of acid or alkali treated cadmium pigments

Abstract Series of cadmium pigments were chemically modified by immersion in acidic and basic conditions. Many changes were documents both for structure and properties of CdS pigments doped with CdSe or ZnS. There were consistently observed changes in saturation of red and a decrease in green hue for sRGB values regardless of the acidity of digesting mixtures. Higher sensitivity to aggressive environment for pigments with higher CdSe doping was noticed. However, linear trend was broken after reaching 1:1 ratio of CdS: CdSe behind which again pigment were less prone to chemical digestion. The structural changes were described by thermogravimetric, methyl blue absorption and RTG diffraction studies. The acidic and basic conditions lead to change of increase of crystalline phase by digesting mainly amorphous part. This in turn resulted in changes of active adsorption sites increasing yellow pigment specific surface after alkaline treatment and decreasing it due to acidic condition. During pigments digestion in acidic and alkaline conditions their amorphous forms are removed from them which causes an increase in the number of active centers of adsorption.

Near-Infrared Luminescence of Cadmium Pigments: In Situ Identification and Mapping in Paintings

A comprehensive study of the luminescence properties of cadmium pigments was undertaken to determine whether these properties could be used for in situ identification and mapping of the pigments in paintings. Cadmium pigments are semiconductors that show band edge luminescence in the visible range and deep trap luminescence in the red/infrared range. Emission maxima, quantum yields, and excitation spectra from the band edge and deep trap emissions were studied for sixty commercial cadmium pigments that span the color range from yellow to red (reflectance transition 470 to 660 nm). For paints containing cadmium pigments, luminescence from deep traps was more readily observable than that from the band edge, although the yield varied widely from zero to around 4.5%. Optimal excitation for emission is found to be in the visible for both pigments in powder form and mixed with a medium. The maxima of the deep trap emission shift with the band gap energy, providing a potentially useful way to assign pigment type even when used in pigment mixtures. The usefulness of the results of the study on mockups was demonstrated by the mapping of cadmium pigments of different hues with the aid of calibrated luminescence imaging spectroscopy in a painting by Edward Steichen, entitled Study for 'Le Tournesol' (1920). Analysis of the luminescence image cube reveals at least six unique spectral components, associated with emission from white pigments, paint binder, and cadmium red and yellow pigments. The results were compared with those from X-ray fluorescence spectrometry (XRF) and fiber-optic reflection spectroscopy (FORS) and the results obtained on paint samples containing cadmium pigments. These results show that, when present, the emission from traps can be used as an analytical tool to identify cadmium pigments, to distinguish among cadmium sulfide, cadmium zinc sulfide, and cadmium sulfoselenide, and to map cadmium pigments, even in mixtures.

ChemInform Abstract: Inorganic Yellow-Red Pigments Without Toxic Metals.

Inorganic pigments have been utilized by mankind since ancient times, and are still widely used to colour materials exposed to elevated temperatures during processing or application. Indeed, in the case of glasses, glazes and ceramics, there is no alternative to inorganic pigments for colouring. However, most inorganic pigments contain heavy metals or transition metals that can adversely effect the environment and human health if critical levels are exceeded. Cadmium-based pigments in particular are a cause of concern: although the pigments are not toxic due to their very low solubility in water and dilute mineral acids, cadmium itself is toxic and can enter the environment in a bioavailable form through waste-disposal sites and incineration plants. This has led to regulations, based on the precautionary principle, that strongly restrict the use of cadmium pigments. And even though recent assessments have concluded that the risk to humans or the environment might be not as significant as originally feared, a strong demand for inherently safer substitutes remains. Here we demonstrate that solid solutions of the perovskites CaTaO2N and LaTaON2 constitute promising candidates for such substitutes: their brilliance, tinting strength, opacity, dispersability, light-fastness and heat stability rival that of the cadmium pigments, while their colour can be tuned through the desired range, from yellow through orange to deep red, by simple composition adjustments. Because all the constituent elements are harmless, this perovskite-based inorganic pigment system seems a promising replacement that could eliminate one of the sources for cadmium emissions to the environment and some of the remaining concerns about pigment safety.

Cadmium Yellow Detection and Quantification by Voltammetry of Immobilized Microparticles

Cadmium pigments (cadmium sulfide and cadmium sulfoselenide) produce intense colorings such as yellow, orange and red, and are well-known pigments in artists' colors, plastics, glasses, ceramics and enamels. This makes cadmium yellow a widespread pigment and hence is very interesting to develop a simple and fast procedure for its identification. Here we propose a straightforward procedure that is harmless to the sample allowing its application to valuable samples and also to very small samples. Three different electrochemical procedures were developed for the identification and quantification of CdS. They are based on voltammetry of immobilized microparticles that suffer a reductive scan at 60 mVs−1 from +0.30 V to −1.00 V producing peaks whose potential allows identification of the pigment. For quantitative purposes a pretreatment of −1.50 V for 10 s was applied and then an oxidative scan was performed. The relative position of the Cd oxidation peak to the peak potential of an internal standard (AgCl) was used to proceed to the calibration.

Cadmium colours: composition and properties

The composition and the properties of cadmium aquarelle colours are discussed. The examined colours were 24 different aquarelle cadmium colours from six different manufacturers. The colours ranged from light, bright yellows to dark, deep-red tones. The aim of this research was to find out if the pigments contain cadmium salts: sulphides and/or selenides. This information will help in choosing watercolours in conservation processes. Today, aquarelle colours not containing cadmium pigments are being sold as cadmium colours; thus their properties might be different from actual cadmium colours. The aim of the research was to verify that the colour samples contained cadmium pigments and to estimate their compositions and ageing properties. Element analyses were performed from colour samples using micro-chemical tests and X-ray fluorescence measurements. Thin-layer chromatography was used for analysing gum Arabic as a possible binding medium in the chosen colour samples. Through ageing tests, the resistance of the colour samples to the exposure to light, heat and humidity was studied. Visible-light spectroscopy was used in determining the hues and hue changes of the aquarelle colour samples. The spectrophotometer used the CIE L*a*b* tone colour measuring system. From the colour measurements the changes in the lightness/darkness, the redness, the yellowness and the saturation of the samples were examined.

Micro-Raman analysis of coloured lithographs.

Raman micro-spectroscopy was chosen for analysis and identification of the pigments present in four nineteenth-century hand-coloured lithographs, as this technique has several advantages over others for this purpose. The possibility of performing completely non-destructive analysis without any sampling is probably one of its most favourable qualities for art analysis. Raman spectroscopy can also be used to determine some pigments that cannot be detected using FTIR, such as vermilion, carbon blacks, cadmium pigments, etc. Among others, Prussian blue, ultramarine blue, carbon black, chrome yellow, yellow ochre, red lead, red iron oxide, burnt Sienna, indigo blue, chrome orange, phthalocyanine green, and some other organic pigments, were determined in the specimens. The results obtained have led to doubts about the age of the lithographs.

Nature and origin of black spots found on Miró paintings: a non-invasive study

The degradation mechanism of cadmium pigments in an oil painting by Joan Miró is determined and reproduced. All possible chemical reactions leading to the observed alteration are checked in laboratory conditions. The behaviour of the different materials (support, pigments and binding medium) are determined. The study of the reaction and products is made using optical microscopy, scanning electron microscopy (SEM) with an energy dispersive X-ray detector, Fourier transform infrared spectroscopy and X-ray diffraction.

Inorganic yellow-red pigments without toxic metals

Inorganic pigments have been utilized by mankind since ancient times, and are still widely used to colour materials exposed to elevated temperatures during processing or application. Indeed, in the case of glasses, glazes and ceramics, there is no alternative to inorganic pigments for colouring. However, most inorganic pigments contain heavy metals or transition metals that can adversely effect the environment and human health if critical levels are exceeded. Cadmium-based pigments in particular are a cause of concern: although the pigments are not toxic due to their very low solubility in water and dilute mineral acids, cadmium itself is toxic and can enter the environment in a bioavailable form through waste-disposal sites and incineration plants. This has led to regulations, based on the precautionary principle, that strongly restrict the use of cadmium pigments. And even though recent assessments have concluded that the risk to humans or the environment might be not as significant as originally feared, a strong demand for inherently safer substitutes remains. Here we demonstrate that solid solutions of the perovskites CaTaO2N and LaTaON2 constitute promising candidates for such substitutes: their brilliance, tinting strength, opacity, dispersability, light-fastness and heat stability rival that of the cadmium pigments, while their colour can be tuned through the desired range, from yellow through orange to deep red, by simple composition adjustments. Because all the constituent elements are harmless, this perovskite-based inorganic pigment system seems a promising replacement that could eliminate one of the sources for cadmium emissions to the environment and some of the remaining concerns about pigment safety.

Laser-Induced Fluorescence in Artwork Diagnostics: An Application in Pigment Analysis

The applicability of laser-induced fluorescence (LIF) spectroscopy as a nondestructive analytical technique for artwork diagnostics is investigated. In this work, LIF is employed in the examination of a set of cadmium sulfide- and cadmium selenide sulfide-based pigments in a series of oil painting test samples. Fluorescence spectra of the oil colors are recorded upon pulsed laser excitation at 532, 355 (Nd:YAG), and 248 nm (KrF excimer). The technique is shown to be suitable for differentiating among the various cadmium pigments used in this study and, furthermore, to be capable of identifying individual components in mixtures of these pigments on the basis of their characteristic fluorescence emission. Future prospects and the potential for the extension of LIF from a research laboratory technique into a conservator's tool for artwork diagnostics are discussed.