J. Molera

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.

Lustre Recipes from A Medieval Workshop in Paterna

The discovery of the workshop ‘Les Olleries Xiques’ in Paterna has provided a unique opportunity to analyse the raw materials, and in particular the recipes used in the production of the lustre decorations. Chemical and phase analyses of lustre raw materials and of lustre decorations belonging to the workshop pottery are shown. A comparison with existing ancient documentation on lustre recipes is also presented.

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.

Composition, nanostructure, and optical properties of silver and silver-copper lusters

Lusters are composite thin layers of coinage metal nanoparticles in glass displaying peculiar optical properties and obtained by a process involving ionic exchange, diffusion, and crystallization. In particular, the origin of the high reflectance (golden-shine) shown by those layers has been subject of some discussion. It has been attributed to either the presence of larger particles, thinner multiple layers or higher volume fraction of nanoparticles. The object of this paper is to clarify this for which a set of laboratory designed lusters are analysed by Rutherford backscattering spectroscopy, transmission electron microscopy, x-ray diffraction, and ultraviolet-visible spectroscopy. Model calculations and numerical simulations using the finite difference time domain method were also performed to evaluate the optical properties. Finally, the correlation between synthesis conditions, nanostructure, and optical properties is obtained for these materials.

X-ray structural characterization, raman and thermal analysis of LiNaSO4. The phase diagram of the Li2SO4-Na2SO4 system

An accurate structural study on the β-phase of LiNaSO4 was carried out. This study shows that twin crystals are usually obtained when crystallization takes place from solution, which explains the observed low spontaneous polarization. Raman scattering of Li2SO4, Na2SO4 and LiNaSO4 is explained from the structural data. The phase diagram of the binary system Li2SO4-Na2SO4 was determined by x-ray diffraction and the DTA method. Mixed crystals of the low-temperature phase of Li2-xNaxSO4 with 1≤x≤1.22 were observed for the first time. The temperatures of the process in this diagram are high, depending on the cooling rate. A more congruent diagram was obtained working at a lower cooling rate.

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).

Metallic and nonmetallic shine in luster: An elastic ion backscattering study

Luster is a metal glass nanocomposite layer first produced in the Middle East in early Islamic times (9th AD) made of metal copper or silver nanoparticles embedded in a silica-based glassy matrix. These nanoparticles are produced by ion exchange between Cu+ and Ag+ and alkaline ions from the glassy matrix and further growth in a reducing atmosphere. The most striking property of luster is its capability of reflecting light like a continuous metal layer and it was unexpectedly found to be linked to one single production parameter: the presence of lead in the glassy matrix composition. The purpose of this article is to describe the characteristics and differences of the nanoparticle layers developed on lead rich and lead free glasses. Copper luster layers obtained using the ancient recipes and methods are analyzed by means of elastic ion backscattering spectroscopy associated with other analytical techniques. The depth profile of the different elements is determined, showing that the luster layer formed in ...

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.