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Research Project
HERCULES Laboratory - Cultural Heritage, Studies and Safeguard
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An insight into the firing conditions of Chinese blue-and-white porcelain through XANES
Publication . Coutinho, ML; Veiga, JP; Ruivo, Andreia; Silva, Teresa; Salas-Colera, Eduardo; Bottura Scardina, Silvia; Lima, Augusta; Figueiredo, Elin; Cotte, Marine; Lima, M.M.R.A.
ABSTRACT: Chinese blue-and-white porcelain is found in archaeological excavations worldwide, being significant evidence of global trade routes and cultural exchange. Synchrotron radiation-based techniques have been applied for studying cobalt speciation to establish a correlation between the cobalt and iron oxidation state and local coordination environment in the rich blue shades of Chinese blue-and-white porcelain. However, the relationship between the firing atmosphere conditions and the speciation of cobalt has not been established yet. In this study, underglaze blue models were produced and fired in air or under reducing atmospheres to ascertain the effect of the firing atmosphere in cobalt and iron speciation. The experimental results were compared with data obtained on historical samples of ancient porcelain shards. The microstructure and colour of the produced underglaze blue models were investigated by variable pressure scanning electron microscopy (VP-SEM-EDS), using a hyperspectral imaging camera (Vis-SWIR reflectance spectroscopy) and colorimetry. The formal valence and coordination of cobalt and iron ions of the glaze were determined by X-ray absorption spectroscopy (XAS), particularly X-ray absorption near edge structure (XANES), using synchrotron radiation. Spectral features demonstrated that both cobalt and iron speciation were affected by the firing atmosphere and therefore could be used to ascertain the firing atmosphere.
Contribution to the Understanding of the Colour Change in Bluish-Grey Limestones
Publication . Silva, Teresa; De Oliveira, Daniel Pipa Soares; Veiga, JP; Lisboa, Jose; Carvalho, Jorge; Barreiros, M. Alexandra; Coutinho, ML; Salas-Colera, Eduardo; Vigário, Rogério
ABSTRACT: Bluish-grey limestones have been extensively used as ornamental stones for decoration purposes in buildings, as well as in works of art, and accordingly, have been the target of intense exploration. In Portugal, the Jurassic limestone massif known as the Macico Calcario Estremenho (MCE), has been the source of grey-coloured ornamental stones, namely the Azul Valverde (one of the most well-known bluish-grey limestones) and Atlantic Blue varieties, both of which may undergo colour changes in outdoor environments. In this sense, it is important to understand the sudden colour change from bluish-grey to yellow/beige in the same limestone block in a quarry, or even, what happens to the colour when polished limestone is placed outdoors. This study was undertaken using various techniques, namely XRF (X-ray fluorescence spectrometry), XRD (X-ray diffraction), SEM (scanning electron microscopy), DTA-TG (differential thermal analysis/thermogravimetry) and colourimetry. Synchrotron radiation was also used at the European Synchrotron Radiation Facility (ESRF, Grenoble, France) where XANES (X-ray Absorption Near Edge Structure) spectra at Fe K-edge were collected to ascertain the speciation state of Fe in different coloured zones of the limestone, previously checked by EDXRF (energy dispersive X-ray fluorescence). The presence of Fe2+ and Fe3+ are responsible for the greyish and yellow/brown colour, respectively. On the other hand, the UV radiation from the sun causes a quickened and severe bleaching/fading on the dark blue/grey polished limestone.
Trace Element Geochemistry of Alluvial TiO2 Polymorphs as a Proxy for Sn and W Deposits
Publication . Gaspar, Miguel; Grácio, Nuno; Salgueiro, Rute; Costa, Mafalda
ABSTRACT: The Segura mining field, the easternmost segment of the Gois-Panasqueira-Segura tin-tungsten metallogenic belt (north-central Portugal), includes Sn-W quartz veins and Li-Sn aplite-pegmatites, which are believed to be genetically related to Variscan Granites. Sediment geochemistry indicates granite-related Ti-enrichments, locally disturbed by mineralization, suggesting magmatic and metamorphic/metasomatic titaniferous phases. Therefore, Segura alluvial samples and the geochemistry of their TiO2 polymorphs (rutile, anatase, and brookite) were investigated, and their potential as exploration tools for Sn and W deposits was evaluated. The heavy-mineral assemblages proved to be good proxies for bedrock geology, and TiO2 polymorph abundances were found to be suitable indicators of magmatic and/or metasomatic hydrothermal processes. The trace element geochemistry of Segura's alluvial rutile, anatase, and brookite is highly variable, implying multiple sources and a diversity of mineral-forming processes. The main compositional differences between TiO2 polymorphs are related to intrinsic (structural) factors, and to the P-T-X extrinsic parameters of their forming environments. Anomalous enrichments, up to 9% Nb, 6% Sn and W, 3% Fe, 2% Ta, and 1% V in rutile, and up to 1.8% Fe, 1.7% Ta, 1.2% Nb, 1.1% W 0.5% Sn and V in anatase, were registered. Brookite usually has low trace element content (<0.5%), except for Fe (similar to 1%). HFSE-rich and granitophile-rich rutile is most likely magmatic, forming in extremely differentiated melts, with Sn and W contents enabling the discrimination between Sn-dominant and W-dominant systems. Trace element geochemical distribution maps show pronounced negative Sn (rutile+anatase) and W (rutile) anomalies linked to hydrothermal cassiterite precipitation, as opposed to their hydrothermal alteration halos and to W-dominant cassiterite-free mineralized areas, where primary hydrothermal rutile shows enrichments similar to magmatic rutile. This contribution recognizes that trace element geochemistry of alluvial TiO2 polymorphs can be a robust, cost- and time-effective, exploration tool for Sn(W) and W(Sn) ore deposit systems.
Characterization of Tableware from Fábrica de Loiça de Sacavém : Linking Analytical and Documental Research
Publication . Coutinho, ML; Veiga, JP; Ruivo, Andreia; Silva, Teresa; Bottura Scardina, Silvia; Lima, M.M.R.A.; Pereira, Carlos; Dias, Ana Carvalho; Dias, Luis; Vandenabeele, Peter; Roseiro, J. Carlos
ABSTRACT: Fabrica de Loica de Sacavem (ca. 1858-1994) was among the first to produce white earthenware in Portugal, becoming one of the country's leading ceramic manufacturers during the late 19th to early 20th centuries. Research on white earthenware has accompanied the growing interest in post-industrial archaeology but is still poorly explored compared to more ancient ceramic productions. This study focused on the ceramic body, glazes, and colourants of tableware produced by Fabrica de Loica de Sacavem during the first 50 years of its activity (1859-1910). A multi-analytical approach was selected to investigate the chemical and mineralogical composition of the ceramic body, glaze, and pigments using optical microscopy, variable-pressure scanning electron microscope energy-dispersive X-ray spectroscopy (VP-SEM-EDS), mu-Raman spectroscopy, mu-X-ray Diffraction (mu-XRD), and reflectance spectroscopy (hyperspectral image analysis). The studied tableware was produced with a Ca-poor siliceous-aluminous white earthenware ceramic body covered with transparent alkali lead or lead borosilicate glaze, and most colourants were complex Cr-based pigments. These results are in agreement with the little documental evidence from this period found in the manufacturer's archives.
Contact metamorphism and dolomitization overprint on Cambrian carbonates from the Ossa‑Morena Zone (SW Iberian Massif): implications to Sr‑chronology of carbonate rocks
Publication . Roseiro, José; Moreira, Noel; Andrade, Laura; Nogueira, Pedro; de Oliveira, Daniel Pipa Soares; Eguiluz, Luis; Mirao, Jose; Moita, Patrícia; Santos, José Francisco; Ribeiro, Sara; Pedro, J.
ABSTRACT: he Cambrian Series 2 Carbonate Formation from the Alter do Chão Elvas-Cumbres Mayores unit (Ossa-Morena Zone, SW Iberian Massif) is composed of regionally metamorphosed marbles and marlstones that underwent chlorite zone metamorphism and preserve the primaeval limestone 87Sr/86Sr ratios (0.7083–0.7088). These are consistent with the established Lower Cambrian seawater curve, and therefore used for age constraints in formations lacking fossil contents. The regional mineralogical and Sr-isotopic features of the carbonate rocks are frequently overprinted by the effects of contact metamorphism induced by magmatic bodies emplaced during rift-related and synorogenic events of the Palaeozoic, as well as by post-metamorphic dolomitization processes. The development of calc-silicate minerals due to contact metamorphism is common in the rocks of the Carbonate Formation and apparently results from the interaction of the protolith with fluids of different origin: (i) internally produced fluids released by conductive heating (observed in external contact aureoles) and (ii) external intrusion-expelled fluids that, besides leading to the appearance of distinctive assemblages, also promote an influx of strontium content (observed in roof pendants). Calc-silicate mineralogy varies substantially throughout the region, likely due to the heterogeneous distribution of silicate minerals of the protolith, progression of intrusion-driven fluids, and the irregular effect of thermal gradients. Results suggest that high-grade contact metamorphism (hornblende facies or higher) and dolomitization processes imposed on the Carbonate Formation significantly influence the isotopic signatures of the carbonates, providing limitations in applying Sr-isotopic chronology.
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Funding agency
Fundação para a Ciência e a Tecnologia
Funding programme
6817 - DCRRNI ID
Funding Award Number
UIDB/04449/2020