Raman spectroscopy as a means for the identification of plattnerite (PbO2), of lead pigments and of their degradation products

Pb nanospheres encapsulated in metal-organic frameworks-derived porous carbon as anode for high-performance sodium-ion batteries

Alloying-type anode materials are considered promising candidates for sodium-ion batteries (SIBs) due to their high theoretical capacities. However, their application is limited by the severe capacity decay stemming from dramatic volume changes during Na+ insertion/extraction processes. Here, Pb nanospheres encapsulated in a carbon skeleton (Pb@C) were successfully synthesized via a facile metal-organic frameworks (MOFs)-derived method and used as anodes for SIBs. The nanosized Pb particles are uniformly incorporated into the porous carbon framework, effectively mitigating volume changes and enhancing Na+ ion transport during discharging/charging. Benefiting from this unique architecture, a reversible capacity of 334.2 mAh g-1 at 2 A g-1 is achieved after 6000 cycles corresponding to an impressive 88.2 % capacity retention and a minimal capacity loss of 0.00748 % per cycle. Furthermore, a high-performance full sodium-ion battery of Pb@C//NVPF was constructed, demonstrating a high energy density of 291 Wh kg-1 and power density of 175 W kg-1. This facile MOFs-derived method offers insights into the design of high-capacity alloy-type anode materials using Pb sources, opening up new possibilities for innovative approaches to Pb recycling and pollution prevention.

Rapid and sensitive in situ detection of heavy metals in fish using enhanced Raman spectroscopy

Heavy metals have been widely applied in industry, agriculture, and other fields because of their outstanding physics and chemistry properties. They are non-degradable even at low concentrations, causing irreversible harm to the human and other organisms. Therefore, it is of great significance to develop high accuracy and sensitivity as well as stable techniques for their detection. Raman scattering spectroscopy and atomic absorption spectrophotometer (AAS) were used parallelly to detect heavy metal ions such as Hg, Cd, and Pb of different concentrations in fish samples. The concentration of the heavy metals is varied from 5 ppb to 5 ppm. Despite the satisfactory recoveries of AAS, their drawbacks are imperative for an alternative technique. In Raman scattering spectroscopy, the intensities and areas of the characteristic peaks are increased with increasing the concentration of the heavy metals. For Hg concentration ≥ 1 ppm, a slight shift is observed in the peak position. The obtained values of peak intensity and peak area are modeled according to Elvoich, Pseudo-first order, Pseudo-second order, and asymptotic1 exponential model. The best modeling was obtained using the Elovich model followed by the asymptotic1 exponential model. The introduced Raman spectroscopy-based approach for on-site detection of trace heavy metal pollution in fish samples is rapid, low-cost, and simple to implement, increasing its visibility in food safety and industrial applications.

Time and spatially resolved VIS-NIR hyperspectral imaging as a novel monitoring tool for laser-based spectroscopy to mitigate radiation damage on paintings

The increased adoption of non-invasive laser-based techniques for analysis of cultural assets has recently called into question the non-invasiveness of the techniques in practical operation. The methods to assess the occurrence of radiation-induced alteration on paintings are very limited and none of them can predict damage. Here we present a novel multimodal imaging approach to understand the time and spatial evolution and types of laser-induced surface alterations, through simultaneous monitoring using visible and near infrared (VIS-NIR) reflectance hyperspectral imaging (HSI) and thermal imaging during Raman spectroscopy. The resultant physical and chemical changes were examined in detail by optical coherence tomography and synchrotron based micro-X-ray powder diffraction. HSI was found to be the most sensitive in detecting laser induced alternations compared with conventional methods. It is orders of magnitude more sensitive than Raman spectroscopy and even synchrotron-based micro-X-ray powder diffraction. In cases of thermally driven alterations, transient and reversible reflectance changes were found to be the first indications of laser-induced modifications and can therefore be used as precursors to prevent damage. VIS-NIR reflectance spectroscopy should be used to monitor laser-based analysis and potentially other radiation-based techniques in situ to mitigate laser induced alteration.

Raman Study of 532-Nanometer Laser-Induced Degradation of Red Lead

Red lead is commonly employed as a red pigment in numerous valuable cultural artifacts. Raman spectrometry has been widely employed as the primary tool in many nondestructive studies on red lead. Therefore, it is necessary to evaluate and study the impact of lasers on the pigment. The degradation of red lead induced by a 532 nm laser is investigated using micro-Raman spectroscopy. At room temperature, red lead begins to degrade into β-PbO when the power density of the 532 nm laser reaches approximately 5.1 × 104 W/cm2 (laser: 532 nm, objective: 50×). At this point, the temperature at the focus of the sample is estimated to be at least 500 °C, aided by the Raman peak shift of β-PbO. Furthermore, the power density of the laser-induced degradation decreases as the temperature of the red lead increases. Hence, the degradation of red lead can be attributed to the photothermal effect. The temperature rise can be explained by two factors. First, red lead exhibits a high absorbance of approximately 0.5942 at 532 nm. Second, red lead has significantly low thermal diffusivity and conductivity, measuring 0.039 mm2·s-1 and 0.078 W·m-1·K-1, respectively, which leads to heat accumulation at the focal point of the laser beam. To better preserve cultural heritage, the appropriate laser power should be prioritized when the degradation process is caused by the thermal effect of laser irradiation.

Lead in the Presence of Iron under Alkaline Conditions for the Oxygen-Evolution Reaction

The oxygen-evolution reaction (OER) is a bottleneck in water splitting, which is a critical process for energy storage. In this study, the electrochemistry of Pb in the absence or presence of K2FeO4, as a soluble Fe source, is examined at pH ≈ 13. Our findings indicate that Pb exhibits limited catalytic activity for the OER under alkaline conditions. However, upon the addition of K2FeO4 to the electrolyte, a significant enhancement in the OER activity is observed in the presence of Pb. A notable observation in this study is the formation of stable Fe(IV) species following the OER during chronoamperometry experiments conducted in an alkaline solution. In addition to in situ Raman and visible spectroscopies, the operated electrodes have been characterized by high-resolution transmission electron microscopy, scanning electron microscopy, electron spin resonance spectroscopy, X-ray diffraction, electrochemical methods, electron paramagnetic resonance, and X-ray absorption spectroscopy. Through our experimental investigations, it is consistently observed that the presence of Fe ions on the surface of Pb/PbOx serves as an effective catalyst for the OER. However, it is important to note that this heightened OER activity is only temporary due to the low adhesion of Fe ions on the surface of Pb/PbOx.

Mesostructured lead dioxide grown on titania nanotubes for diclofenac water removal through electrocatalytic and photoelectrocatalytic processes

Mesostructured PbO2/TiO2 materials were synthesized to perform electrocatalysis (as electrooxidation, EO) and photoelectrocatalysis for removing diclofenac (DCF), 15 ppm concentration in 0.1 M NaSO4 solutions, at different pH conditions (3.0, 6.0 and 9.0) by applying 30 mA cm-2. Titania nanotubes (TiO2NTs)-based materials were prepared to synthetize with a massive PbO2 deposit on this support to obtain TiO2NTs/PbO2 and a TiO2NTs:PbO2 material consisting in a dispersed PbO2 deposit on TiO2-NTs that allowed the formation of a heterostructured surface of combined composition (TiO2 and PbO2). Organics removal (DCF and byproducts) was monitored through UV-vis spectrophotometry and high-performance liquid chromatography (HPLC) during degradation tests. TiO2NTs/PbO2 electrode was tested in both processes, removing DCF at neutral and alkaline solution conditions in EO while an unimportant photoactivity was registered at this material. Conversely, TiO2NTs:PbO2 was used as electrocatalytic material in EO experiments, achieving more than 50% of DCF removal at pH 6.0 by applying 30 mA cm-2. Also, for first time, the synergic effect was investigated when it was exposed to UV irradiation in photoelectrocatalytic experiments, enhancing its efficacy (⁓more than 20%) to remove DCF from a solution with 15 ppm over performance removals achieved (56%) when EO was applied under similar conditions. Chemical Oxygen Demand (COD) analyses showed that significantly higher DCF degradation is reached under photoelectrocatalysis, since COD values decrease a 76% against a 42% decrease achieved with electrocatalysis. Scavenging experiments showed a significant participation on the pharmaceutical oxidation process through the generation of photoholes (h+), hydroxyl radicals and sulfate-based oxidants.

A Possible Natural and Inexpensive Substitute for Lapis Lazuli in the Frederick II Era: The Finding of Haüyne in Blue Lead-Tin Glazed Pottery from Melfi Castle (Italy)

The blue color of glass and ceramic glazes produced in Apulia and Basilicata (Southern Italy) between the 13th and 14th centuries and connected to the Norman-Swabian Emperor Frederick II, has been, for a long time, under archaeometric investigation. On the one hand, it has usually been associated with lapis lazuli, due to the finding of the polysulphide blue chromophores typical of lazurite. Moreover, the observation that the mineral haüyne, which belongs to the sodalite group as well as lazurite, can be blue and/or can gain a blue color after heating, due to the same chromophores, has caused this automatic attribution to be questioned, and also considering that the mineral is characteristic of the rock haüynophyre of Melfi (Potenza, Southern Italy), a location of interest for glass and pottery findings. In this paper, for the first time, several haüyne crystals were found in the blue glaze of a ceramic dish found at Melfi Castle, leading to the hypothesis that, in this case, the local haüyne-bearing source could have been used as the coloring raw material. The discovery was possible thanks to SEM-EDS and Raman analyses that, respectively, highlighted the typical numerous presence of very fine sulphur-based inclusions in the crystals and the characteristic Raman signal of blue haüyne. This study was also focused on the composition of the crystals inclusions, aided by SEM-EDS and Raman maps, since the original very fine pyrrhotite was transformed into Cu and Pb phases (copper sulphates, copper sulphides, and lead oxide) due to reactions with cations that had mobilized from the glaze, while the migration of Si from the glass allowed the transformation of the rim of the haüyne, a silica-undersaturated mineral, into a corona of small euhedral and neomorphic Pb-rich feldspars, a silica-saturated phase.

Fractal algorithms and RGB image processing in scribal and ink identification on an 1819 secret initiation manuscript to the "Philike Hetaereia"

Historical texts incorporate important characteristics that need to be assessed including genre, text structure and content. Often overlooked are characteristics of handwritten manuscripts commonly divided into legibility, readability and aesthetics. To determine the scientific feasibility of classification of handwritten texts an objective approach is developed to describe twenty handwritten pages of an 1819 Greek manuscript, that refers to the initiation to the Greek secret "friendly society" (Philike Hetaereia) organization, established as part of the Greek independence against the Ottoman Turks. It is investigated through a fractal and RGB image analysis approach. Fractal Minkowski Dimension was applied on the handwritten text and the RGB color analysis on the ink and paper and both were used as a non-invasive manner and revealed interesting results. The novel RGB image analysis and the fractal analysis of the manuscript identified respectively, five iron gall inks and four scribes from the ink content and handwritten styles, of the compact five lines text and whole text pages. The novel approach was verified with another old manuscript of known ink pigments, as well as with thirteen known handwritten texts of that period and four prints representing modern and similar period texts substantiating the findings of the novel methods.

English delftware (c. 1770) from Bristol, Lancaster and Liverpool: A composition study using Raman spectroscopy and electron microscopy

Nine decorated lead-tin glazed earthenwares, colloquially termed 'delftware', produced in c. 1770 in Bristol, Lancaster and Liverpool, England, have been analysed non-invasively by Raman spectroscopy and electron microscopy. The body paste used to manufacture these west coast wares was attained by the blending of highly dolomitic [CaMg(CO₃)₂] "blue" clay sourced from Carrickfergus, County Antrim, Ireland, with locally sourced clays. Thus, the resulting body fabric of these wares contains significant MgO enabling them to be differentiated from MgO-free London manufactured delftware. The glazes employed all contain arsenic, obtained as a cobalt impurity or by deliberate addition. The presence of this unvolatilised arsenic in the glaze has then reacted with the lead during firing at temperatures approaching 1000 °C and then further reacted with calcium and magnesium to form needle-like crystals of lead arsenates in the form of mimetite [Pb₅(AsO₄)(Cl,OH)], schulténite [Pb(AsO₃OH)], β-roselite [Ca₂Co(AsO₄)₂·2H₂O], hedyphane [Ca₂Pb₃(AsO₄)₃Cl], wendwilsonite [Ca₂Mg(AsO₄)₂·2H₂O] and/or adelite [CaMgAsO₄(OH)] during high temperature firing.

A study of potential laser-induced degradation in remote standoff Raman spectroscopy for wall paintings

A mobile remote standoff Raman spectroscopy system operational at typical distances of 10 m was developed specifically for research of historical sites and wall paintings recently. Here we present an upgrade to that system informed by a thorough experimental investigation of the relevant laser-induced degradation issues. Reflectance spectroscopy as a more sensitive technique than Raman spectroscopy was used for monitoring and a new phenomenon of reversible alterations was detected in many paint samples at very low laser intensities of less than 1 W/cm² when Raman measurements detected no changes. Contrary to conventional wisdom, the intensity threshold for safe operation was found to decrease significantly for larger incident irradiation area in the case of a vermilion oil paint sample. Damage threshold in intensity for each material needs to be determined for different spot sizes, which can be orders of magnitude lower for 1 mm spot size compared with micro-Raman. Results from this study is also relevant to portable Raman systems which use similarly large spot sizes. However, the larger spot size still generates more Raman photons overall under safe operation than micro-Raman systems. Continuous-wave (CW) lasers are found to be best suited to efficient, that is more Raman signal detected over a given measurement time, and safe Raman operation than ns-pulse lasers at the same wavelength. While the damage threshold in intensity for ns-pulse lasers is much higher than that of CW lasers, the pulse energy allowed in one pulse for safe operation is still too low to allow detection of Raman signal, and the need for multiple pulses makes pulse laser inefficient owing to the low repetition rate necessary to ensure adequate heat dissipation between pulses. The safety of the upgraded system was evaluated and found that no permanent laser-induced degradation was detected within 60 s of laser irradiation for any of the paint samples.

Raman focal point on Roman Egyptian blue elucidates disordered cuprorivaite, green glass phase and trace compounds

The discussed comparative analyses of Roman Imperial pigment balls and fragmentary murals unearthed in the ancient cities of Aventicum and Augusta Raurica (Switzerland) by means of Raman microspectroscopy pertain to a predecessor study on trace compounds in Early Medieval Egyptian blue (St. Peter, Gratsch, South Tyrol, Northern Italy). The plethora of newly detected associated minerals of the raw materials surviving the synthesis procedure validate the use of quartz sand matching the composition of sediments transported by the Volturno river into the Gulf of Gaeta (Campania, Southern Italy) with a roasted sulphidic copper ore and a mixed-alkaline plant ash as fluxing agent. Thus, the results corroborate a monopolised pigment production site located in the northern Phlegrean Fields persisting over the first centuries A.D., this in line with statements of the antique Roman writers Vitruvius and Pliny the Elder and recent archaeological evidences. Beyond that, Raman spectra reveal through gradual peak shifts and changes of band width locally divergent process conditions and compositional inhomogeneities provoking crystal lattice disorder in the chromophoric cuprorivaite as well as the formation of a copper-bearing green glass phase, the latter probably in dependency of the concentration of alkali flux, notwithstanding that otherwise solid-state reactions predominate the synthesis.

A Study of Song Dynasty Polychrome Statue-Making Techniques and Materials in the Sage Mother Hall of the Jinci Temple, Shanxi, China

The polychrome statues of the Sage Mother Hall at the Jinci Temple in Taiyuan city are recognized as one of the three masterpieces of the Jinci Temple. They are also regarded as an outstanding representative of ancient Chinese temple statues. These statues possess great historical, artistic, scientific, cultural and social values, and they are an important physical material for the study of ancient Chinese history, culture, religion, politics and economy, as well as science and technology. The internal structure, plaster layer samples and surface pigments of the polychrome statues of the Sage Mother Hall were analyzed by optical microscope (OM) scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM–EDS), X-ray powder diffraction (XRD), Raman spectroscopy (Raman), X-radiography and other analytical methods in order to gain an understanding of the production process and pigment composition of the polychrome statues of the Sage Mother Hall. According to the findings, the following steps were taken during the production of the polychrome statues that decorate the Sage Mother Hall at Jinci Temple: building a wooden skeleton, fixing the skeleton with rivets or twine, shaping the clay form with coarse clay, shaping the appearance with fine clay, refining the molded appearance, and white substrate layer painting. The majority of the pigments are inorganic mineral pigments: the red pigments include cinnabar and minium; the blue pigments include ultramarine; the green pigments include lavendulan; the yellow pigments include yellow ochre; the black pigments include carbon black; and the white pigments and substrate layers include white lead and lead sulfate. Some of the pigment layers can be seen in multiple layers, which indicates that over the history of the painted statues of the Sage Mother Hall, they have been subject to a series of repainting, with the more recent repainting time perhaps having taken place during the late Qing Dynasty and the following time period.

Plasmonic Nb2CTx MXene-MAPbI3 Heterostructure for Self-Powered Visible-NIR Photodiodes

The ability of MXenes to efficiently absorb light is greatly enriched by the surface plasmons oscillating at their two-dimensional (2D) surfaces. Thus far, MXenes have shown impressive plasmonic absorptions spanning the visible and infrared (IR) regimes. However, their potential use in IR optoelectronic applications, including photodiodes, has been marginally investigated. Besides, their relatively low resistivity has limited their use as photosensing materials due to their intrinsic high dark current. Herein, heterostructures made of methylammonium lead triiodide (MAPbI₃) perovskite and niobium carbide (Nb₂CT_x) MXene are prepared with a matching band structure and exploited for self-powered visible-near IR (NIR) photodiodes. Using MAPbI₃ has expanded the operation range of the MAPbI₃/Nb₂CT_x photodiode to the visible regime while suppressing the relatively large dark current of the NIR-absorbing Nb₂CT_x. In consequence, the fabricated MAPbI₃/Nb₂CT_x photodiode has responded linearly to white light illumination with a responsivity of 0.25 A/W and a temporal photoresponse of <4.5 μs. Furthermore, when illuminated by NIR laser (1064 nm), our photodiode demonstrates a higher on/off ratio (∼10³) and faster response times (<30 ms) compared to that of planar Nb₂CT_x-only detectors (<2 and 20 s, respectively). The performed space-charge-limited current (SCLC) and capacitance measurements reveal that such an efficient and enhanced charge transfer depends on the coordinate bonding between the surface groups of the MXene and the undercoordinated Pb²⁺ ions of the MAPbI₃ at the passivated MAPbI₃/Nb₂CT_x interface.

Multitechnique diagnostic analysis and 3D surveying prior to the restoration of St. Michael defeating Evil painting by Mattia Preti

In this study, a multimethodological analysis involving optical and physical/chemical diagnostic techniques and 3D photogrammetric survey was successfully applied, for the first time, on the large oil on canvas St. Michael defeating Evil painting by Mattia Preti, located inside the Church of the Immaculate Conception of Sarria (Floriana) in Malta. Pigmenting agents, binder media, and raw materials were first characterized, both at elemental and molecular scales, through X-ray fluorescence spectroscopy (XRF), optical stereo microscopy (SM), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), Fourier transform infrared spectroscopy (FT-IR), and gas chromatography coupled with mass spectrometry (GC-MS). The main goal was to properly identify the execution technique of this famous painter, the artist's palette, and possible nondocumented interventions. The 3D photogrammetric survey, on the other side, allowed us to noninvasively evaluate the extension of the areas that experienced restorations, and to properly map the domains of the different canvasses observed. The joints between canvasses suggested that the painting was folded and rolled up. In addition, the employment of a thermal camera gave evidence of the different consolidating material injection points used during the restoration to strengthen the painting. The obtained results offer useful information for the development of optimized restoration and conservation strategies to be applied and provide, at the same time, answers to open questions related to provenance and dating of the investigated artwork.

The combined use of SEM-EDX, Raman, ATR-FTIR and visible reflectance techniques for the characterisation of Roman wall painting pigments from Monte d'Oro area (Rome): an insight into red, yellow and pink shades

The aim of this work has been the identification of the painter's materials employed in the wall decoration of some destroyed buildings dating approximately between the first century B.C. and the first century A.D. This research originates from a previously started joined archaeological and analytical investigation concerning a varied group of findings that resulted from a rescue excavation performed by Soprintendenza Archeologica in the area of Monte d'Oro in Rome. The focus of this study progression has been directed to a numerous selection of monochrome red, pink and yellow-pigmented fragments. The analyses were performed by means of scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDX) combined with Raman and Fourier transform infrared (FTIR) spectroscopies; visible reflectance measurements have also been carried out and the relevance of this technique in such a kind of archaeological studies has been highlighted. Most attention has been given to the assessment of the performances of non-destructive techniques achieved by portable Raman, and visible reflectance instrumentation to test their diagnostic capabilities. In addition to the expected and well-known pigments such as cinnabar, red ochre, hematite for the reds and yellow ochre for the yellows, the study highlighted a diffuse use of mixed colours and in some cases the possible presence of overlapped painted layers and confirmed the presence of gildings. Among the mixtures of pigments, the most singular outcome concerns the pink fragments revealing the possible application of bone white, which seems to be rather uncommon as a pigment in Roman wall decorations.

Multi-Technique Diagnostic Investigation in View of the Restoration of “The Glory of St. Barbara” Painting by Mattia Preti

The present paper illustrates the results of a diagnostic investigation performed on the oil on canvas painting “The Glory of St. Barbara” (1680–1688) by Mattia Preti. The painting is located inside the St. Barbara Church in Taverna (Catanzaro, Italy), the city that gave birth to the artist. In situ, non-invasive studies, by applying X-ray fluorescence (XRF) spectroscopy, along with laboratory micro-destructive analytical investigations, by employing electron probe microanalyses (EPMA) coupled with energy-dispersive spectrometry (EDS) and micro-Raman (µ-Raman) spectroscopy, were combined to retrieve the color palette and identify the painting technique and style of the famous master. As a result of this multi-scale characterization, an extraordinary pictorial technique was revealed, enriching knowledge about one of the oldest pictorial traditions outlined by Mattia Preti, and solving doubts still existing about many of his investigated artworks. Moreover, the achieved results represent useful and essential tools to address management issues of the artwork, by providing valuable information for planning and monitoring future restoration interventions of the canvas.

Novel Chemoresistive Sensor for Sensitive Detection of Pb2+ Ions Using an Interdigital Gold Electrode Fabricated with a Reduced Graphene Oxide-Based Ion-Imprinted Polymer

This study presents novel chemoresistive reduced graphene oxide-ion-imprinted polymer (IIP-rGO)-based sensors for detection of lead (Pb2+) ions. The ion-imprinted polymer was synthesized by bulk polymerization and modified with a variable amount of rGO incorporated to form an IIP-rGO composite. The amount of rGO in the polymer matrix affected the sensor's relative response, and 1:3 mass ratio produced excellent results, with a consistent trend as the concentration of Pb2+ ions increased in the solution. The decrease in relative resistance (ΔR/R o) followed an exponential decay relationship between the ΔR/R o response and the concentration of Pb2+ ions in aqueous solutions. After solving the exponential decay function, it is observed that the sensor has the upper limit of ΔR/R o >1.7287 μg L-1, and the limit of detection of the sensor is 1.77 μg L-1. A nonimprinted polymer (NIP)-based sensor responded with a low relative resistance of the same magnitude although the concentration was varied. The response ratio of the IIP-based sensor to the NIP-based sensor (ΔR/R o)IIP/(ΔR/R o)NIP as a function of the concentration of Pb2+ ions in the solution shows that the response ratios recorded a maximum of around 22 at 50 μg L-1 and then decreased as the concentration increased, following an exponential decay function with the minimum ratio of 2.09 at 200 μg L-1 but never read 1. The sensor showed excellent selectivity against the bivalent cations Mn2+, Fe2+, Sn2+, and Ti2+. The sensor was capable of exhibiting 90% ΔR/R o response repeatability in a consecutive test.

Nanoscale Analysis of Historical Paintings by Means of O-PTIR Spectroscopy: The Identification of the Organic Particles in L'Arlésienne (Portrait of Madame Ginoux) by Van Gogh

Optical-photothermal infrared (O-PTIR) spectroscopy is a recently developed technique that provides spectra comparable to traditional transmission FTIR spectroscopy with nanometric spatial resolution. Hence, O-PTIR is a promising candidate for the analysis of historical paintings, as well as other cultural heritage objects, but its potential has not yet been evaluated. This work presents the first application of O-PTIR to the analysis of cultural heritage, and in particular to an extremely small fragment from Van Gogh's painting L'Arlésienne (portrait of Madame Ginoux). The striking results obtained, including the detection of geranium lake pigments as well as the complete analysis of the stratigraphy, failed with other state-of-the-art techniques, highlight the potential of this method. The integration of O-PTIR to the study of cultural heritage opens to the possibility of decreasing the amount of sample extracted, therefore contributing to the preservation of the integrity of artworks while providing a complete characterization of the materials.

Reviving Alexander Calder’s Man-Eater with Pennants: A Technical Examination of the Original Paint Palette

Man-Eater with Pennants, a rarely exhibited sculpture in Alexander Calder’s oeuvre, was commissioned by The Museum of Modern Art (MoMA) and installed in 1945. To exhibit the large standing mobile in Alexander Calder: Modern from the Start (2021), the derelict sculpture had to be remediated; this initiated a collaborative investigation with conservation scientists, conservators, curators, and the Calder Foundation into the original paint colors hidden beneath layers of repaint. XRF analysis was carried out to elucidate the paints’ composition, followed by sampling for analysis to assess the paint stratigraphy and binders. Scrapings were analyzed by µ-FTIR and Raman spectroscopies; cross sections were examined with optical microscopy and analyzed with SEM-EDS. Analysis differentiated between the original paints, which contain Prussian blue, parachlor red, chrome yellow, and the many layers of overpaint, which contain titanium white, molybdate orange, a variety of β-Naphthol reds, red lead, and ultramarine. A model for Man-Eater, Mobile with 14 Flags, is also part of the museum’s collection, and was first considered as a point of reference for the original colors. Similar analysis, however, indicates that the maquette was painted after the Man-Eater was first installed, therefore is not representative of the original colors. In addition to investigating an early primary palette for Calder’s outdoor sculptures, this study helped develop the plan for the restoration of the original color scheme of Man-Eater.

Trace compounds in Early Medieval Egyptian blue carry information on provenance, manufacture, application, and ageing

Only a few scientific evidences for the use of Egyptian blue in Early Medieval wall paintings in Central and Southern Europe have been reported so far. The monochrome blue fragment discussed here belongs to the second church building of St. Peter above Gratsch (South Tyrol, Northern Italy, fifth/sixth century A.D.). Beyond cuprorivaite and carbon black (underpainting), 26 accessory minerals down to trace levels were detected by means of Raman microspectroscopy, providing unprecedented insights into the raw materials blend and conversion reactions during preparation, application, and ageing of the pigment. In conjunction with archaeological evidences for the manufacture of Egyptian blue in Cumae and Liternum and the concordant statements of the antique Roman writers Vitruvius and Pliny the Elder, natural impurities of the quartz sand speak for a pigment produced at the northern Phlegrean Fields (Campania, Southern Italy). Chalcocite (and chalcopyrite) suggest the use of a sulphidic copper ore, and water-insoluble salts a mixed-alkaline flux in the form of plant ash. Not fully reacted quartz crystals partly intergrown with cuprorivaite and only minimal traces of silicate glass portend solid-state reactions predominating the chemical reactions during synthesis, while the melting of the raw materials into glass most likely played a negligible role.

A systematic investigation on synergistic electroplating and capacitive removal of Pb2+ from artificial industrial waste water

A capacitive deionization cell designed with symmetric activated carbon electrodes was demonstrated to be able to successfully reduce wastewater Pb²⁺ concentrations to below the 5 ppm statuary limited for discharge into public sewers. The investigation found that the removal efficiency shows a maximum of 98% with an initial Pb²⁺ concentration of 100 ppm under an optimized voltage of 1.3 V. Although the reversibility of the process was poor during the first charge/discharge cycle, in part due to cathodic electrodeposition of lead hydroxycarbonates, this was improved by acidification of the electrolyte and subsequent cycles showed good reversibility. Finally, it was demonstrated that Na⁺ ions, with 50% removal efficiency and 100% reversibility, do not interfere with either the removal rate of Pb²⁺ ions or the reversibility of this process, providing a new angle on desalination applications for the system.

Schematic description of Pb²⁺ removal based on capacitive electrochemical technique.

Intrinsic Valley Polarization and High-Temperature Ferroelectricity in Two-Dimensional Orthorhombic Lead Oxide

Recent years have witnessed a surge of research in two-dimensional (2D) ferroelectric structures that may circumvent the depolarization effect in conventional perovskite oxide films. Herein, by first-principles calculations, we predict that an orthorhombic phase of lead(II) oxide, PbO, serves as a promising candidate for 2D ferroelectrics with good stability. With a semiconducting nature, 2D ferroelectric PbO exhibits intrinsic valley polarization, which leads to robust ferroelectricity with an in-plane spontaneous polarization of 2.4 × 10^-10 C/m and a Curie temperature of 455 K. Remarkably, we reveal that the ferroelectricity is strain-tunable, and ferroelasticity coexists in the PbO film, implying the realization of 2D multiferroics. The underlying physical mechanism is generally applicable and can be extended to other oxide films such as ferroelectric SnO and GeO, thus paving an avenue for future design and fabrication of functional ultrathin devices that are compatible with Si-based technology.

Ochre-Based Pigments in the Tablinum of the House of the Bicentenary (Herculaneum, Italy) between Decorative Technology and Natural Disasters

Ochre-based pigments have been employed since the first artistic expressions of mankind, with widespread diffusion during the Roman civilization. Such prominent use influenced their technological development, focused on functional and aesthetic optimization through complex manufacturing procedures. Furthermore, their appearance is also influenced by degradation processes, sometimes driven by natural disasters such as the eruption of Mount Vesuvius in 79 AD, in which yellow ochres of Vesuvian sites were sometimes converted to red by thermal alteration. In this contribution, a multi-analytical approach was adopted based on preliminary non-invasive investigations complemented by laboratory analyses to characterize the painted surfaces of the tablinum of the House of the Bicentenary (Herculaneum) with a particular focus on the ochre-based monochrome backgrounds. The study was aimed at (a) reconstructing the original color scheme of the walls and (b) deciphering the complex decorative techniques adopted by Roman craftsmen. The analytical results allowed testing and defining analytical procedures for the discrimination between the original and converted red pigments. Furthermore, these studies indicated that specific decorative technologies were adopted according to aesthetic, functional, and economic purposes, including the utilization of various qualities of ochre with different compositional and textural properties, and the mixture of ochre pigments with other compounds.

Investigation of proteinaceous paint layers, composed of egg yolk and lead white, exposed to fire-related effects

Fires can have a negative impact on the environment, human health, property and ultimately also on various objects of cultural heritage (CH). This paper deals with an investigation into the degradation of selected proteinaceous paint layers that were exposed to fire-related effects (i.e., fire effluents and/or high temperatures) in a modified cone-calorimeter system. Paint layers of egg yolk adhesive (E) and lead white tempera (E + LW) were exposed to fire-related impacts on top of a CH stack and in a specially designed CH test chamber. On the CH stack, the proteinaceous paint layers were exposed to fire effluents and high temperatures, while in the CH test chamber, the samples were exposed mainly to fire effluents. The molecular changes to the exposed paint layers were analysed by invasive and non-invasive spectroscopic analyses (i.e., FTIR and Raman spectroscopy) and complimented with pyrolysis-GC–MS, while the colour changes were evaluated using colourimetry. It was concluded that the proteinaceous binder degrades into aromatic amino acids and/or fatty acids after exposure to the overall impacts of the fire. Aromatic amino acids were detected by means of the FTIR and py-GC–MS analyses. In the case of the lead white tempera exposure, partial dissociation of the lead white pigment was confirmed by the detection of alteration products, such as lead oxide and lead carbonate. Moreover, the investigation of the E + LW samples exposed for longer times revealed the presence of lead carboxylates. On the other hand, no significant molecular changes were observed with the CH samples exposed to fire effluents in the CH test chamber. The research offered us an insight into the fire-induced effects on selected paints for the first time.

Oxidation of Mn(III) Species by Pb(IV) Oxide as a Surrogate Oxidant in Aquatic Systems

Dissolved Mn(III) species have been recognized as a significant form of Mn in redox transition environments, but a holistic understanding of their geochemical properties still lacks the characterization of their reactivity as reductants. Through using PbO₂ as a surrogate oxidant and pyrophosphate (PP) as a model ligand, we evaluated the thermodynamic and kinetic constrains of dissolved Mn(III) oxidation under environmentally relevant pH. Without disproportionation, Mn(III) complexes could be directly oxidized by PbO₂ to produce Mn oxides. The reaction rates decreased with increasing PP:Mn(III) ratio and became negligible when the ratio was above a threshold value. Particulate manganite could also be oxidized by PbO₂ with detectable production of Pb(II). The favorability of Mn(III) oxidation by PbO₂ as a function of the PP:Mn ratio could be predicted by the stability constant of the Mn(III)-PP complex. We developed kinetic models that couple multiple pathways of Mn oxidation by PbO₂ to simulate the dynamics of Pb release, loss of dissolved Mn, as well as Mn(III) production and consumption. Beyond the context of Mn geochemistry, the interactions between Pb and various Mn species, including its trivalent forms, may also have important implications to the water quality in lead service lines within distribution systems.

Spectroscopic investigation and comprehensive analysis of the polychrome clay sculpture of Hua Yan Temple of the Liao Dynasty

This article shows the investigation results of the polychrome clay sculptures in Hua Yan Temple of the Liao Dynasty in Datong, China. The mineral pigments, adhesive and painting techniques used in these cultural relics were systematically analyzed in this project. Optical microscope (OM), Scanning electron microscope coupled with an energy-dispersive X-ray spectroscopy (SEM-EDS), micro-Raman, Fourier transform infrared spectrometer (FT-IR) and Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) analyses were selected as scientific micro-destructive analytical methods. The results show that the pigments in the polychrome clay sculptures include cinnabar, lead red, malachite, atacamite, azurite, orpiment and gold. Meanwhile, the presence of nitrogen-containing substances and glue-marker characteristic pyrolysis products clearly indicates that the adhesive used in most of the polychrome clay sculptures was glue-protein. Additionally, the combination of heat-bodied tung oil and glue-protein was also found in the golden areas.

Pigments on Roman Wall Painting and Stucco Fragments from the Monte d’Oro Area (Rome): A Multi-Technique Approach

This work concerns the characterisation of a set of wall painting and stucco fragments collected during a rescue excavation carried out in 2013 by the Soprintendenza Archeologica in the Monte d’Oro area (Rome). Due to the contextless archaeological situation, analyses were performed to obtain more information about the collected materials. A multi-analytical approach has been applied including spectroscopic (FTIR, Raman and visible reflectance analyses) and elemental analysis (SEM-EDS) techniques. The chromatic palette has been in this way disclosed evidencing the use of pigments such as cinnabar, Egyptian blue, red and yellow ochre and green earth, but also the simultaneous use of them. The presence of a decoration achieved by using a gold leaf has been highlighted also, indicating the preciousness of the decorations. The convenience and advantages linked to the use of portable instrumentation have been also evidenced.

Use of Temperature Controlled Stage Confocal Raman Microscopy to Study Phase Transition of Lead Dioxide (Plattnerite)

The present work concerns the study of the phase transition of plattnerite [β-PbO2 lead (IV) oxide]-based samples when they are analysed by Raman spectroscopy. The laser-induced degradation process was carried out either on historical painting samples, where plattnerite was present as a degradation product of lead-based pigments, or commercial plattnerite samples as powder and pellets. The Raman spectra of plattnerite taken at low excitation power, to avoid phase transformations, are reported up to low wavenumbers, and they were characterized by the features at 159, 380, 515 and 653 cm−1 and a shoulder at 540 cm−1. The degradation of plattnerite was induced by increasing the laser power on the sample, and the formation of its secondary products red lead (Pb3O4), litharge (α-PbO) and massicot (β-PbO), when varying the laser power, is discussed. The analyses were performed in a controlled condition by coupling the Raman spectrometer to a temperature-controlled stage (Linkam THMS600- Renishaw), which allows for varying the sample temperature (from room temperature up to 600 °C) and keeping it constant inside the stage during the analysis. In this way, commercial plattnerite samples were heated by increasing the cell temperature to verify the temperature range at which the phase transitions of lead dioxide occur. In addition, thanks to the construction of temperature ramps, all the degradation pathways were shown, and other lead compounds were identified, generated by the laser power contribution. A different behaviour was found between pigments from historical painting samples and commercial samples under the effect of the laser. This information could be useful in order to recognize their nature when they are found in cultural heritage materials.

Au/Pb Interface Allows the Methane Formation Pathway in Carbon Dioxide Electroreduction

The electrochemical conversion of carbon dioxide (CO₂) to high-value chemicals is an attractive approach to create an artificial carbon cycle. Tuning the activity and product selectivity while maintaining long-term stability, however, remains a significant challenge. Here, we study a series of Au–Pb bimetallic electrocatalysts with different Au/Pb interfaces, generating carbon monoxide (CO), formic acid (HCOOH), and methane (CH₄) as CO₂ reduction products. The formation of CH₄ is significant because it has only been observed on very few Cu-free electrodes. The maximum CH₄ formation rate of 0.33 mA cm^–2 was achieved when the most Au/Pb interfaces were present. In situ Raman spectroelectrochemical studies confirmed the stability of the Pb native substoichiometric oxide under the reduction conditions on the Au–Pb catalyst, which seems to be a major contributor to CH₄ formation. Density functional theory simulations showed that without Au, the reaction would get stuck on the COOH intermediate, and without O, the reaction would not evolve further than the CHOH intermediate. In addition, they confirmed that the Au/Pb bimetallic interface (together with the subsurface oxygen in the model) possesses a moderate binding strength for the key intermediates, which is indeed necessary for the CH₄ pathway. Overall, this study demonstrates how bimetallic nanoparticles can be employed to overcome scaling relations in the CO₂ reduction reaction.

Interfacial Modification and Defect Passivation by the Cross-Linking Interlayer for Efficient and Stable CuSCN-Based Perovskite Solar Cells

The study of the inorganic hole-transport layer (HTL) in perovskite solar cells (PSCs) is gathering attention because of the drawback of the conventional PSC design, where the organic HTL with salt dopants majorly participates in the degradation mechanisms. On the other hand, inorganic HTL secures better stability, while it offers difficulties in the deposition and interfacial control to realize high-performing devices. In this study, we demonstrate polydimethylsiloxane (PDMS) as an ideal polymeric interlayer which prevents interfacial degradation and improves both photovoltaic performance and stability of CuSCN-based PSC by its cross-linking behavior. Surprisingly, the PDMS polymers are identified to form chemical bonds with perovskite and CuSCN, as shown by Raman spectroscopy. This novel cross-linking interlayer of PDMS enhances the hole-transporting property at the interface and passivates the interfacial defects, realizing the PSC with high power-conversion efficiency over 19%. Furthermore, the utilization of the PDMS interlayer greatly improves the stability of solar cells against both humidity and heat by mitigating the interfacial defects and interdiffusion. The PDMS-interlayered PSCs retained over 90% of the initial efficiencies, both after 1000 h under ambient conditions (unencapsulated) and after 500 h under 85 °C/85% relative humidity (encapsulated).

Standoff Raman spectroscopy for architectural interiors from 3-15 m distances

Portable and mobile Raman spectroscopy systems are increasingly being adopted in in situ non-invasive examination of artworks given their high specificity in material identification. However, these systems typically operate within centimeter range working distances, making the examination of large architectural interiors such as wall paintings in churches challenging. We demonstrate the first standoff Raman spectroscopy system for in situ investigation of historic architectural interior at distances > 3 m. The 780 nm continuous wave laser-induced standoff Raman system was successfully deployed for the in situ examination of wall paintings, at distances of 3-15 m, under ambient light. It is able to identify most common pigments while maintaining a very low laser intensity to avoid light induced degradation. It is shown to complement our current method of standoff remote surveys of wall paintings using spectral imaging.

A multi-analytical approach for the study of red stains on heritage marble

Red stains are a common discolouration on stone cultural heritage all over the world. These are very difficult to remove and little is known about the reddish pigmentation. Numerous red stains were mapped on the Baptistery of San Giovanni in Florence, one of the most important monuments in Italy. This paper is focused on red stains on marble stone and the results of a detailed multidisciplinary approach are presented. Several analytical and investigation techniques (such as optical microscopy, X-ray fluorescence mapping, X-ray micro-tomography, micro-Raman spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, microbial isolation, colorimetric measurements and isotopic analyses) were used to better understand the origin and processes involved in this kind of alteration. Analyses of the red stains led us to believe the presence of minium (lead tetroxide) and Pb are usually concentrated in the spaces between calcite grains. Red stains of Pb isotopic composition also overlap with data from Sardinian mines. These preliminary data seem to reinforce the suggestion of a source of lead from some metallic items (during restoration campaigns between 1938 and 1944, damaged parts were removed and replaced, and the new marble cladding was fixed with iron brackets treated with minium).

Removal of PFAS from aqueous solution using PbO2 from lead-acid battery

Whilst advanced electrochemical oxidation can break down per- and polyfluoroalkyl substances (PFAS), the requirement for expensive electrode materials usually prevents its widespread application. Here we use an industrial material of lead peroxide (PbO₂) from a lead-acid battery to break down PFAS including perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), and 1H,1H,2H,2H-perfluorooctanesulfonic acid (6:2 FTS). By optimising the PbO₂ panel (activating and doping) and working conditions including supporting electrolyte (1 L 10 mM Na₂SO₄), initial concentration (10 μM), temperature (room temperature), current density (5 A for a 10 cm × 10 cm PbO₂ panel) etc., we successfully remove > 99% PFAS (individual PFAS monitored via HPLC-MS) whilst mineralising ∼59% PFOA (defluorination, F^- released and monitored via F-ISE, fluoride-ion selective electrode). By studying the pseudo-first-order kinetics of the PFAS breakdown (0.0028-0.007 min^-1) and defluorination (0.84-5.9 × 10^-8 min^-1), we assign the difference to the adsorption of PFAS on the PbO₂ panel and the appearance of intermediates before the full defluorination. The leaked HF gas (∼10^-5 M, collected using 0.25 L 0.1 M NaOH) and Pb²⁺ (∼12 μM, or ∼ 2.5 ppm) are also confirmed. This study employs an economic industrial material, highlights the contribution of adsorption towards the PFAS removal and breakdown, and identifies the possible leakage of secondary contaminants.

Unraveling the materials and techniques of post-Byzantine wall paintings: Is there a sole pictorial phase at the catholicon of Stomion, Central Greece?

Saint Demetrius of Stomion is a historical monastery placed in the geographical area of Larissa town, Greece, with a remarkable presence from its founding until nowadays. The monastery's present catholicon (main church) has been dated in the 16th century and its surviving wall paintings were constructed in 1758. In addition to the characterization of the materials applied, the purpose of this study is to determine the existence of a sole pictorial phase, that of the mid-18th century, or the occurrence of overpaintings. Additionally, the present study aims to begin the establishment of the documentation of materials and techniques of the late post-Byzantine iconographic guilds, which acted in Central and Northern Greece. The collected samples were analyzed by means of microscopic, spectroscopic and thermogravimetric methods. The use of fresco technique is implied by the major participation of calcium carbonate in all of the painting layers, its main contribution in the plaster layers and the microstratigraphic analysis of the samples' cross-sections, while the scarce and local presence of a proteinaceous material implies the limited use of egg-tempera technique for the highlights. The pigment analysis shows that mostly traditional pigments were used, including cinnabar, ferrous pigments (ochre, sienna, umber), minium, Naples yellow, massicot/litharge, green earth (celadonite), malachite, carbon and bone black, calcite, kaolinite and lead white. The absence of modern pigments, the consistency of all samples regarding microstratigraphy and applied materials, and the lack of the extensive use of an organic medium, strongly suggest the lack of overpaintings.

Stable and Efficient Organo-Metal Halide Hybrid Perovskite Solar Cells via π-Conjugated Lewis Base Polymer Induced Trap Passivation and Charge Extraction

High-quality pinhole-free perovskite film with optimal crystalline morphology is critical for achieving high-efficiency and high-stability perovskite solar cells (PSCs). In this study, a p-type π-conjugated polymer poly[(2,6-(4,8-bis(5-(2-ethylhexyl) thiophen-2-yl)-benzo[1,2-b:4,5-b'] dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl) benzo[1',2'-c:4',5'-c'] dithiophene-4,8-dione))] (PBDB-T) is introduced into chlorobenzene to form a facile and effective template-agent during the anti-solvent process of perovskite film formation. The π-conjugated polymer PBDB-T is found to trigger a heterogeneous nucleation over the perovskite precursor film and passivate the trap states of the mixed perovskite film through the formation of Lewis adducts between lead and oxygen atom in PBDB-T. The p-type semiconducting and hydrophobic PBDB-T polymer fills in the perovskite grain boundaries to improve charge transfer for better conductivity and prevent moisture invasion into the perovskite active layers. Consequently, the PSCs with PBDB-T modified anti-solvent processing leads to a high-efficiency close to 20%, and the devices show excellent stability, retaining about 90% of the initial power conversion efficiency after 150 d storage in dry air.

In Situ Monitoring of Pb2+ Leaching from the Galvanic Joint Surface in a Prepared Chlorinated Drinking Water

A novel method using a micro-ion-selective electrode (micro-ISE) technique was developed for in situ lead monitoring at the water-metal interface of a brass-leaded solder galvanic joint in a prepared chlorinated drinking water environment. The developed lead micro-ISE (100 μm tip diameter) showed excellent performance toward soluble lead (Pb²⁺) with sensitivity of 22.2 ± 0.5 mV decade^-1 and limit of detection (LOD) of 1.22 × 10^-6 M (0.25 mg L^-1). The response time was less than 10 s with a working pH range of 2.0-7.0. Using the lead micro-ISE, lead concentration microprofiles were measured from the bulk to the metal surface (within 50 μm) over time. Combined with two-dimensional (2D) pH mapping, this work clearly demonstrated that Pb²⁺ ions build-up across the lead anode surface was substantial, nonuniform, and dependent on local surface pH. A large pH gradient (ΔpH = 6.0) developed across the brass and leaded-tin solder joint coupon. Local pH decreases were observed above the leaded solder to a pH as low as 4.0, indicating it was anodic relative to the brass. The low pH above the leaded solder supported elevated lead levels where even small local pH differences of 0.6 units (ΔpH = 0.6) resulted in about four times higher surface lead concentrations (42.9 vs 11.6 mg L^-1) and 5 times higher fluxes (18.5 × 10^-6 vs 3.5 × 10^-6 mg cm^-2 s^-1). Continuous surface lead leaching monitoring was also conducted for 16 h.

Optical coherence tomography and non-linear microscopy for paintings - a study of the complementary capabilities and laser degradation effects

This paper examines for the first time the potential complementary imaging capabilities of Optical coherence tomography (OCT) and non-linear microscopy (NLM) for multi-modal 3D examination of paintings following the successful application of OCT to the in situ, non-invasive examination of varnish and paint stratigraphy of historic paintings and the promising initial studies of NLM of varnish samples. OCT provides image contrast through the optical scattering and absorption properties of materials, while NLM provides molecular information through multi-photon fluorescence and higher harmonics generation (second and third harmonic generation). OCT is well-established in the in situ non-invasive imaging of the stratigraphy of varnish and paint layers. While NLM examination of transparent samples such as fresh varnish and some transparent paints showed promising results, the ultimate use of NLM on paintings is limited owing to the laser degradation effects caused by the high peak intensity of the laser source necessary for the generation of non-linear phenomena. The high intensity normally employed in NLM is found to be damaging to all non-transparent painting materials from slightly scattering degraded varnish to slightly absorbing paint at the wavelength of the laser excitation source. The results of this paper are potentially applicable to a wide range of materials given the diversity of the materials encountered in paintings (e.g. minerals, plants, insects, oil, egg, synthetic and natural varnish).

A new approach to the determination of the synthetic or natural origin of red pigments through spectroscopic analysis

This work suggests a way of differentiation between the natural or synthetic origin of inorganic materials that were historically used in the Cultural Heritage field. An exhaustive review of different reported procedures of synthesis of pigments was conducted, as well as a review of the accompanying minerals in case of natural pigments. The natural or synthetic origin of the pigments studied in this work was performed through the characterization of the accompanying minerals, in the case of the natural pigments, or the trace elements that are present as part of synthesis by-products or washing/purifying reagents and/or reactants that have only been partly removed in the final steps of these processes. This work characterized red pigments due to their wide variety, complexity and possibility of use in different mixtures. The following pigments were studied: cinnabar-vermilion, red lead and iron pigments. Also mixtures of these pigments between them and with red lake were also studied. Natural cinnabar was accompanied by silicon oxide (opal, chalcedony or quartz), calcite, clay minerals and, sometimes, pyrite. K together with S indicated a synthetic pigment (vermilion) obtained through the wet method. Nevertheless, K has not been found in layers containing only vermilion in our samples. The presence of Sn in some cases indicated vermilion that came from the dry process. K from the synthesis always appeared in the red lead pigment. The red natural ochre was confirmed by presence of clay minerals and iron. It should be said that Ca and S, and sometimes Al and K, were usually found in Mars red pigment. The presence of Al and Ca allowed the identification of carmine lake.

Visualisation and quantification of heavy metal accessibility in smelter slags: The influence of morphology on availability

The Imperial Smelting Furnace (ISF) for producing lead and zinc simultaneously has operated on four continents and in eleven countries from the 1950's. One of the process changes that the ISF introduced was the production of a finely granulated slag waste. Although this slag contained significant amounts of residual lead (Pb) and zinc (Zn), because of its glassy nature it was considered environmentally benign. From the Cockle Creek smelter near Boolaroo at the northern end of Lake Macquarie, NSW, Australia, it is estimated that around 2.1 million tonnes of the fine slag was distributed into the community and most remains where it was originally utilised. Residual tonnages of slag of this magnitude are common worldwide wherever the ISF operated. Studies of base metal smelting slags have concluded that mineralogical and morphological characteristics of the slag play a critical role in moderating environmental release of toxic elements. Scanning electron microscopy (SEM) and microanalysis of the ISF slags has shown that the Pb and associated elements are present as discrete nodules (∼6-22 μm) in the slag and that they are not associated with Zn which is contained in the glass slag phase. Using an automated SEM and analysis technique (QEMSCAN(®)) to "map" the mineralogical structure of the particles, it was possible to quantitatively determine the degree of access infiltrating fluids might have to the reaction surface of the Pb phases. The level of access decreases with increasing particle size, but in even the largest sized particles (-3350 + 2000 μm) nearly 80% of the Pb-containing phases were totally or partially accessible. These results provide evidence that the toxic elements in the slags are not contained by the glassy phase and will be vulnerable to leaching over time depending on their individual phase reactivity.