Teresa Pereira Silva

Monitoring the removal of soluble salts from ancient tiles by ion chromatography

The application of ion chromatography, conductometry and total carbon analysis to the study of desalination of 18th century tiles and mortars is described. Ion chromatography is shown to be a simple and adequate technique for the identification and quantitative analysis of ions which are extracted during desalination. Chloride, nitrate, sulphate, carbonate, sodium, potassium, calcium and magnesium were always found in the immersion waters, and occasionally also nitrite and oxalate.

The Positive Environmental Contribution of Jarosite by Retaining Lead in Acid Mine Drainage Areas

Jarosite, KFe3(SO4)2(OH)6, is a secondary iron sulphate often found in acid mine drainage (AMD) environments, particularly in mining wastes from polymetallic sulphide ore deposits. Despite the negative environmental connotation usually ascribed to secondary sulphate minerals due to the release of hazardous elements to aquifers and soils, jarosite acts as an efficient remover and immobilizer of such metals, particularly lead. The mineral chemistry of jarosite is reviewed and the results of a Fe K-edge XANES (X-Ray Absorption Near-Edge Structure) study of K-, Na- and Pb-jarosite are described and discussed within the context of the abandoned old mines of São Domingos and Aljustrel located in southern Portugal, in the Iberian Pyrite Belt (IPB).

Effect of oxygen sharing on the white line of S K-edge XANES spectra of sulphate minerals

Sulphur occurs under a diversity of formal oxidation states being simultaneously an essential plant nutrient and an environmental pollutant. Intermediate formal valences between 6+ (sulphate) and 4+ (sulphite) were assigned by previous authors in soil colloids by X-ray absorption spectroscopy; a search for similar electronic states was undertaken by analyzing near-edge details preceding the strong white line of S 1 s XANES spectra in well crystallized sulphates depending on the structural arrangement. Sulphate minerals illustrating a variety of sharing degrees of oxygen anions between tetrahedral groups [SO 4 ] and transition metal cations, ranging from non-bonded, isolated tetrahedra to fully shared oxygen anions, were selected for the spectroscopic study. Differences in details appearing at the shoulder of the intense white line of fully oxidized sulphur were successfully correlated with the crystal structural features of these model minerals, showing that intermediate valence states of sulphur resulting from the sharing of oxygen anions may be also present in crystalline sulphates.

Diagnosis of pathologies in ancient (seventeenth-eighteenth centuries) decorative blue-and-white ceramic tiles : Green stains in the glazes of a panel depicting Lisbon prior to the 1755 earthquake

Abstract Decorative panels of ceramic glazed tiles comprise a valuable cultural heritage in Mediterranean countries. Their preservation requires the development of a systematic scientific approach. Exposure to an open-air environment allows for a large span of deterioration effects. Successfully overcoming these effects demands a careful identification of involved degradation processes. Among these, the development of micro-organisms and concomitant glaze surface staining is a very common effect observed in panels manufactured centuries ago. This paper describes a study on the nature of green stains appearing at the surface of blue-and-white tile glazes from a large decorative panel with more than one thousand tiles, called Vista de Lisboa that depicts the city before the destruction caused by the 1755 earthquake. The characterization of green-stained blue-and-white tile glazes was performed using non-destructive X-ray techniques (diffraction and fluorescence spectrometry) by directly irradiating the surface of small tile fragments, complemented by a destructive scanning electron microscopy (SEM) observation of one fragment. Despite the green staining, analytical X-ray data showed that no deterioration had occurred irrespective of the blue or white color, while complementary SEM-EDX data provided chemical evidence of microorganism colonization at the stained glaze surface.

Decorative 18th Century Blue-and-White Portuguese Tile Panels: A Type-Case of Environmental Degradation

Decorated glazed ceramic tiles are used as an ornamental art, constituting an important cultural heritage whose preservation is mandatory. Environmental conditions are responsible for the degradation of exposed ancient tile panels originating various pathologies, related to the development of microorganisms. This is the case of a valuable 18th century blue-and-white Portuguese tile panel called “Cura do Cego,” belonging to the collection of the National Tile Museum (MNAz), where green stains are nowadays observable in the glaze. A prospective diagnosis of this green tarnishing was the aim of the present work. Small tile fragments were directly irradiated using nondestructive techniques: X-ray fluorescence spectrometry with a wavelength-dispersive system (WDXRF) for chemical characterization of the tile glaze and X-ray powder diffraction (XRD) to assess the phase constitution of both the glaze and the ceramic body. A destructive technique (scanning electron microscopy with energy-dispersive system (SEM/EDS)) was applied to tentatively infer the chemical changes induced in the glaze by the green staining and also to characterize the morphology of the microorganisms associated to this staining. The obtained results are reported and discussed, as a preliminary step for testing an innovative nondestructive decontamination technique applying gamma radiation, particularly suitable for overcoming such tile pathologies.