The mineralogy and chemistry of the German and Portuguese tiles used to face a historic building in the Amazon region and their natural susceptibility to tropical weathering

Abstract

During the 19th century, the most prominent buildings of the city of Belém were faced entirely with tiles manufactured in Portugal and Germany, which now exhibit distinct degrees of degradation. The Pinho mansion is one of the most important of these buildings and was selected for the investigation of the action of the tropical Amazonian climate on the degradation of the tiles. To achieve this objective, the tiles were mapped for organic and inorganic degradation, and samples were collected for analysis. The minerals were determined by XRD, the chemical composition by classical wet methods and SEM/EDS, and the microorganisms under the microscope. The results show that the German and Portuguese tiles are quite different in their composition. While both ceramic bodies are composed of SiO 2 and Al 2 O 3 , CaO was found only in the Portuguese tile. The low Na 2 O and K 2 O contents indicate the addition of materials to reduce the fusion temperature. SiO 2 and PbO are the main constituents of the glaze, with CoO and FeO being added as pigment. The ceramic body of the German tiles is constituted of quartz, mullite, and cristobalite, in contrast with the Portuguese tiles, which are made of quartz, gehlenite, diopside, calcite, and feldspars. The glazes are XRD-amorphous. The chemical and mineralogical differences between the German and Portuguese tiles indicate that they were produced from different raw materials under distinct thermal processes. The most prominent weathering-related modifications are the thin layers (German tiles), oxidation stains, dark stains, the detachment of the tile (Portuguese tiles), loss of the glaze and powdering of the ceramic body (Portuguese tiles) through the establishment of Cyanophyta and Bacillariophyta.. The distinct degradation patterns of the tiles exposed to the tropical Amazon climate are a consequence of their distinct mineralogy and chemistry. KEYWORDS: German and Portuguese tiles, degradation, tropical weathering, Amazon region Mineralogia e química de azulejos Alemães e Portugueses de prédios históricos na região Amazônica e sua susceptibilidade natural à degradação tropical (intemperismo) RESUMOAs proeminentes edificações da cidade de Belém foram revestidas durante o século 19 com azulejos produzidos em Portugal e Alemanha que já apresentam distintos graus de degradação. O Palacete Pinho é uma das mais importantes destas edificações e foi selecionado para se investigar a ação do clima tropical amazônico sobre a degradação destes azulejos. Para atingir estes objetivos mapearam-se os azulejos desta edificação visando identificar as modificações de origem orgânica e inorgânica e coletas de amostras para análises. Os minerais foram determinados por DRX, a composição química por métodos clássicos úmidos e MEV/SED e os micro-organismos por microscopia. Os resultados obtidos mostram que os azulejos Portugueses e Alemães são distintos entre si. Enquanto o biscoito é composto de SiO 2 e Al 2 O 3 , CaO foi encontrado apenas nos Portugueses. Os baixos conteúdos de Na 2 O e K 2 ...

The historical glazed tiles from Nossa Senhora da Soledade Cemetery, Northern Brazil: microstructural, physical and mineralogical characterization

“…The result of this production process is observed in the heterogeneity of the ceramic layer of Soledade tiles. The chemical composition identified in the ceramics matrixes in this study is characteristic of Portuguese tiles from this period [7]. The addition of materials to the paste, such as feldspars, phosphates, carbonates, sea salt and volcanic ash, was common in order to decrease the firing temperature [7].…”

“…The chemical composition identified in the ceramics matrixes in this study is characteristic of Portuguese tiles from this period [7]. The addition of materials to the paste, such as feldspars, phosphates, carbonates, sea salt and volcanic ash, was common in order to decrease the firing temperature [7]. So, elements such as sodium and potassium, present in Soledade ceramic samples, may have been added as fluxes.…”

“…So, elements such as sodium and potassium, present in Soledade ceramic samples, may have been added as fluxes. The percentage of Fe 2 O 3 found in Soledade samples is responsible for the yellow color of the ceramic [7,17]. The PbO concentrations in the ceramic of sample AZ.C11 probably came from a contamination of glaze components through the porosity of the material.…”

“…The base of the vitreous matrix is composed primarily of PbO and SiO 2 , with additions of other elements such as CaO and K 2 O used as fluxes, possibly in the form of a calcium carbonate and a K-feldspar [5,7]. Tin predominates in the white glaze, used extensively in the Portuguese manufacture of majolica stamp and relief tiles from the seventeenth to the nineteenth centuries, because it guarantees the separation of chromophore oxides and the opacity of the glaze [6,[8][9][10][11][12].…”

“…The content of silicon, calcium and magnesium in the Soledade samples indicates the use of clays rich in carbonates, or the addition of carbonates to raw material, which may be one of the causes for the presence of vacuoles in the glaze and voids in the ceramic, since these compounds decompose during firing and release CO 2 [7]. These defects can even be caused by retraction fissures or presence of organic matter in the paste, which also release CO 2 during firing [4].…”