M. Vendrell-Saz

The colours of Ca-rich ceramic pastes: origin and characterization

The colour changes found in the wall thickness of archaeological calcareous ceramics are analysed. The main colour change from creamy to reddish is due to the incorporation of Fe3+ in several calcium silicates and aluminosilicates developed during firing. Iron appears as iron oxides (haematite and maghemite) and as structural iron, either in tetrahedral coordination related to the dehydrated clay minerals and to the melilites, or in octahedral coordination related to the pyroxenes of fassaite–diposide type. The creamy colour is related to the complete decomposition of calcite, a significant development of pyroxenes, and to the low presence of iron oxides. Haematite is determined across the creamy and reddish layers except in the outer surface, where maghemite is determined. The presence of maghemite and Fe2+ in the outer surfaces agrees with the use of a low reducing atmosphere at the end of the firing process.

Identification of copper-based green pigments in Jaume Huguet's Gothic altarpieces by Fourier transform infrared microspectroscopy and synchrotron radiation X-ray diffraction

The scientific investigation of ancient paintings gives a unique insight into ancient painting techniques and their evolution through time and geographic location. This study deals with the identification of the green pigments used by one of the most important Catalan masters in Gothic times, Jaume Huguet. Other pigments and materials have also been characterized by means of conventional techniques such as optical microscopy, scanning electron microscopy and Fourier transform infrared spectroscopy. Synchrotron radiation X-ray diffraction has been used to produce maps of phases at a spatial resolution of 100 microm across chromatic layers.

The growth of sanidine crystals in the lead of glazes of Hispano-Moresque pottery

Abstract The nature and the formation of minute sanidine crystals which appear in the sine of the glaze of some Hispano-Moresque pottery from a 14th century A.D. medieval workshop at the Testar del Moli, in Paterna (Valencia, Spain), were studied by scanning electron microscopy. The identification and refinement of the lattice parameters were carried out from the X-ray diffraction spectra that coincide with the above-mentioned feldspar. The chemical composition of the small crystals was studied by means of electronic microprobe, which revealed the presence of 5% lead joined to the lattice substituting the potassium positions. In conclusion, we deduce some technological implications concerning the process of manufacture, especially as regards the cooling of the melt phase.

The red–orange patina developed on a monumental dolostone

Orange and reddish patinas developed on a dolostone of the cathedral of Lleida (Spain) have been analysed and characterised by XRD, SEM/EDX, ICP/MS, optical microscopy and Mossbauer spectroscopy. From the experimental data, a biologically induced transformation of the dolomite rock forming crystals, which form a dolomitic patina of micrite size, can be stabilised. Furthermore, the iron oxides as determined by Mossbauer spectroscopy play a role as colouring patina, together with organic matter from the bioactivity. Erosive and constructive processes, as determined through the SEM observations, lead to aesthetical and microstructural changes in the stone surface.

Mass Spectrometric and Synchrotron Radiation based techniques for the identification and distribution of painting materials in samples from paints of Josep Maria Sert

BackgroundEstablishing the distribution of materials in paintings and that of their degradation products by imaging techniques is fundamental to understand the painting technique and can improve our knowledge on the conservation status of the painting. The combined use of chromatographic-mass spectrometric techniques, such as GC/MS or Py/GC/MS, and the chemical mapping of functional groups by imaging SR FTIR in transmission mode on thin sections and SR XRD line scans will be presented as a suitable approach to have a detailed characterisation of the materials in a paint sample, assuring their localisation in the sample build-up. This analytical approach has been used to study samples from Catalan paintings by Josep Maria Sert y Badía (20th century), a muralist achieving international recognition whose canvases adorned international buildings.ResultsThe pigments used by the painter as well as the organic materials used as binders and varnishes could be identified by means of conventional techniques. The distribution of these materials by means of Synchrotron Radiation based techniques allowed to establish the mixtures used by the painter depending on the purpose.ConclusionsResults show the suitability of the combined use of SR μFTIR and SR μXRD mapping and conventional techniques to unequivocally identify all the materials present in the sample and their localization in the sample build-up. This kind of approach becomes indispensable to solve the challenge of micro heterogeneous samples. The complementary interpretation of the data obtained with all the different techniques allowed the characterization of both organic and inorganic materials in the samples layer by layer as well as to establish the painting techniques used by Sert in the works-of-art under study.

Environmental impact on the Roman monuments of Tarragona, Spain

The extant remains of the Roman monuments of Tarragona, Spain are made of different types of Miocenic rocks from the quarries surrounding the city, which vary from calcarenite to bioclastic limestones, showing different degrees of dolomitization, depending on their diagenetic evolution. The decay of these monuments is highly dependent on the mineralogy and the fabric of the stone as well as on the environmental conditions to which the monument subjected. As a consequence, different forms of decay are observed on these monuments, namely, granular disintegration, differential erosion between sparitic and micritic areas of the rock, and development of black crust and orange patinas, some of them attributed to a sulfation process. A number of processes have been established as being responsible for the decay forms observed: sulfation on sheltered areas of the building in the urban environment; differential dilatation because of the NaCl of the marine spray that crystallizes inside the porosity; hydric and thermal expansion of the stone, both related to the amount and crystallinity of the clay minerals forming the rock matrix; and biocolonization on the stone surface. An empirical model is proposed to explain the decay forms studied in relation to these factors (rock and environment).

Nature and origin of black spots found on Miró paintings: a non-invasive study

The degradation mechanism of cadmium pigments in an oil painting by Joan Miro is determined and reproduced. All possible chemical reactions leading to the observed alteration are checked in laboratory conditions. The behaviour of the different materials (support, pigments and binding medium) are determined. The study of the reaction and products is made using optical microscopy, scanning electron microscopy (SEM) with an energy dispersive X-ray detector, Fourier transform infrared spectroscopy and X-ray diffraction.

Analytical study of the behaviour of some ingredients used in lustre ceramic decorations following different recipes

Ceramic lustre is a fine decoration obtained by a complex technical process. Although the general production technique is more or less known, it is much more difficult to specify the ingredients mixed in the ancient recipes used to produce lustre and their function during the process, especially components as mercury sulphide and iron oxide. To understand this point, mixtures of the components were previously characterised and tested to see which mixtures resulted in the desired lustre. Synchrotron-Radiation-Source X-ray Diffraction (SRS–XRD) of the fired mixtures was performed to check the changes produced in the ingredients. Also Voltammetry of immobilised Microparticles was applied to the raw pigment powders to obtain information about the redox behaviour. Square-wave voltammetry demonstrates the possibility of different deposits that can be formed in the first steps of the reduction process in the pigment mixture for lustre production, especially those related to solid-form reactions and pigment-electrolyte interactions. Moreover, SR–XRD shows the formation of different crystalline phases at the end of the process, in this case probably also related to gas–solid interactions and to a strong reduction atmosphere.

Islamic and Hispano-Moresque (múdejar) lead glazes in Spain: a technical approach

Abstract Islamic and Hispano-Moresque glazes from the 10th to 15th centuries found in various archaeological sites, most of them workshops, are studied to show the technical evolution of the medieval glazing process. The technology seems to show a simplification: the early Islamic glazes were applied on prefired bodies and after fritting a lead-silica mixture, whereas for the later Islamic productions the raw materials for the lead glazes were not fritted and they were applied over unfired bodies. The same simplified technology was used in the Hispano-Moresque workshops. In the Islamic workshops lead glazes were coloured by adding elements (Fe, Cu, Mn), whereas the múdejar technology simplified the process by using only one recipe to produce pots of different colour. This was achieved by applying the glaze in a different manner (on one side of the pot to obtain yellow or on both sides to obtain green), or using different pastes (already used to produce pottery for different uses). Finally, there are differences between Islamic and Hispano-Moresque tin glazes related to the crystal size of the opacifier (tin oxide crystals), which should indicate some technological differences in temperature, glaze composition and the process to obtain the frits because of the high dependence between viscosity, temperature and crystal nucleation and growth.