Search Results (4)

A total of forty samples of medieval and modern glazed pottery from northern Spain were studied. Chemical and microstructural analyses of the glazes were performed by scanning electron microscopy coupled with electron dispersive spectroscopy (SEM-EDX), while the chemical composition of the pottery bodies and slips were determined by X-ray Fluorescence (XRF). The glazes studied come from the Santa Barbara Hill site (Tudela), the Treviño Castle site (Treviño), the Vega workshop (Burgos) and the Torrentejo village (Labastida) and correspond to transparent glazes and opaque white glazes. Transparent glazes were lead glazes with variable PbO content. Opaque white glazes were lead-tin and lead–alkaline–tin glazes. The glaze was mainly applied to a pre-fired body made of local clays, but the glazes of the Santa Barbara Hills pottery (Tudela) were applied to raw bodies. The microstructure of the interfaces indicates a single firing process for the glazed pottery from Tudela and a double firing process in the rest of the sites. Some correlation are identified between the use of specific clays to produce different glaze colours. White opaque glazes are applied to calcium-rich clays. Similarly, calcium-rich clays were used to produce dark green transparent glazes, while clays and slips aluminium–rich were used to produce light green and light honey glazes. Iron was also identified as the main colouring agent, although copper was also used. The white glazes were opacified by the addition of cassiterite and sometimes quartz and feldspar. The glazed pottery was mainly of local origin, but the identification of some non-local pottery at all sites suggests a pottery trade. Full article

Ceramic sherds from approximately 20 samples of lead-glazed tableware, recovered from diverse archaeological sites, including three repurposed storage pits transformed into dumpsters within the medieval city of Santarém (13th–14th century), underwent a meticulous examination. This investigation utilised techniques such as micro-Raman, ground-state diffuse reflectance absorption, and X-ray fluorescence spectroscopies, in addition to X-ray diffraction and stereomicroscopy. A parallel study was conducted on contemporaneous European ceramics (glazed sherds) sourced from archaeological sites dating back to the 13th–15th centuries in Saintonge (France), Ardenne, Zomergem, and Bruges (Belgium), as well as Surrey–Hampshire, Kingston, and Cheam (England). The first premise for comparing the Santarem samples with European production locations was their frequent commercial relations with Portugal and the frequency of these productions being found in Portugal. The colour of the ceramic bodies is predominantly white or whitish, with a few exhibiting a vivid red hue. Analyses of the fabric, mineralogical, and elemental composition of the sherds suggest that the majority of Santarém’s glazed ceramics were locally or regionally produced, potentially derived from a Pliocene kaolin-rich sand formation. However, this conclusion is not supported by the absence of discovered lead glaze kilns or workshops in Santarém for the late Middle Ages. Full article

The 18th century roof tiles from the “Casa delle vigne”, located in the Aosta region (north-east Italy), were investigated as an example of a peculiar historical roof covering: ceramic tiles with a lead-based glaze finishing to waterproof them are used to create colourful patterns. A conservation project proposed the integration of the original tiles with new ones, produced according to traditional methods. Ancient and new tiles were analysed with Fiber Optics Reflectance Spectroscopy, micro-Raman, Fourier Transform Infrared Spectroscopy and X-ray Fluorescence Spectrometry, Thermogravimetry and Differential Scanning Calorimetry for understanding the composition and the production technology of this manufacture. Their resistance to freezing and thawing cycles was then tested, considering their exposure in the severe alpine climate of Aosta. The use of pure clays with low calcium contents, high firing temperature and lead-rich glazes was found in ancient tiles, able to outstand several freezing-thawing cycles without damages. Iron and copper pigments were used in old yellow and green glazes. Zinc-based pigment, low lead and calcium-rich glazes are used in the new ones, which remained mainly coherent to the ceramic body during the freeze-thaw test. Full article

This study considers the limitations of cobalt violet orthophosphate, Co₃P₂O₈, in the ceramic industry due to its large amount of cobalt. Mg_xCo_3−xP₂O₈ (0 ≤ x ≤ 3) solid solutions with the stable Co₃P₂O₈ structure were synthesised via the chemical coprecipitation method. The formation of solid solutions between the isostructural Co₃P₂O₈ and Mg₃P₂O₈ compounds decreased the toxically large amount of cobalt in this inorganic pigment and increased the melting point to a temperature higher than 1200 °C when x ≥ 1.5. Co₃P₂O₈ melted at 1160 °C, and compositions with x ≥ 1.5 were stable between 800 and 1200 °C. The substitution of Co(II) with Mg(II) decreased the toxicity of these materials and decreased their price; hence, the interest of these materials for the ceramic industry is greater. An interesting purple colour with a* = 31.6 and b* = −24.2 was obtained from a powdered Mg_2.5Co_0.5P₂O₈ composition fired at 1200 °C. It considerably reduced the amount of cobalt, thus improving the colour of the Co₃P₂O₈ pigment (a* = 16.2 and b* = −20.1 at 1000 °C). Co₃P₂O₈ is classified as an inorganic pigment (DCMA-8-11-1), and the solid solutions prepared were also inorganic pigments when unglazed. When introducing 3% of the sample (pigment) together with enamel, spreading the mixture on a ceramic support and calcining the whole in an electric oven, a colour change from violet to blue was observed due to the change in the local environment of Co(II), which could be seen in the UVV spectra of the glazed samples with the displacement of the bands towards higher wavelengths and with the appearance of a new band assigned to tetrahedral Co(II). This blue colour was also obtained with Co₂SiO₄, MgCoSiO₄ or Co₃P₂O₈ pigments containing a greater amount of cobalt. Full article