A multi-analytical approach was used to study the pictorial layers of a set of 17th century historic glazed tiles (azulejos) of Portuguese manufacture. The pictorial layer was studied by-EDXRF,-Raman, SEM-EDS and OM. Although the established palette comprises few pigments, it was found that the tiles were enhanced by the use of pigment mixtures, which were identified by-Raman and-EDXRF. As expected, the blue colour derives from cobalt oxide, purple from manganese oxide and emerald-green from copper oxide. Regarding the yellow pigment,-Raman results show it is consistent with the composition of a ternary oxide, whereas-EDXRF shows a high intensity of Zn in this colour, indicating a composition close to a Pb-Sb-Zn ternary oxide. Some compounds from the original ores were also indentified: in two very dark blue samples, cobalt and nickel olivines (␣-Co 2 SiO 4 , ␣-Ni 2 SiO 4), and in a dark brown sample, braunite (a manganese silicate).

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ABSTRACT:The mass consolidation treatment of azulejos is necessary when ceramic biscuits show signs of disaggregation. Such treatment is often used as a complementary conservation technique to the reestablishment of weakened glaze-ceramic bonds. In this research, two commonly used consolidants (ethyl silicate and acrylic resin) were tested on artisanal ceramic tiles via mass consolidation and the resulting impregnation profiles were evaluated. The results indicated that after consolidation, hard zones frequently formed due to localized consolidant concentration after the polymerization and curing processes. These inhomogeneous hard zones subsequently influenced the results obtained through conventional mechanical strength testing (i.e. flexural and compression), creating a false impression of success. This research demonstrated that by using the Drilling Resistance Measuring System, impregnation characteristics such as penetration depth and distribution of consolidant could be observed that otherwise could not be discerned through the more common testing methods. As such, a more extensive evaluation of consolidation effects was achieved. RESUMEN: Tratamientos de consolidación aplicados en materiales cerámicos: ¿Son homogéneos?En la conservación de los azulejos alterados se utilizan productos con acción consolidante a fin de recuperar la cohesión del cuerpo cerámico disgregado. En este trabajo se investiga el efecto de la consolidación de dos productos muy utilizados en la práctica de la conservación de los azulejos (un silicato de etilo comercial y una resina acrílica), aplicados en un material cerámico artesanal. Los resultados obtenidos indican que pueden producirse zonas con resistencias mayores debido a la concentración local del producto y, a la vez de un material consolidado homogéneo, resulta un material heterogéneo. Por otro lado, la existencia de estas zonas puede conducir a falsos resultados en los ensayos destructivos (resistencia mecánica a la flexión y compresión) utilizados frecuentemente en la evaluación de la acción de consolidación. Se demuestra que mediante el uso de la resistencia a la perforación (DRMS) es posible definir las características, la distribución y el patrón de impregnación, los cuales no pueden ser observadas por los métodos comúnmente utilizados.

A systematization of glaze spalling in azulejos Resumo O destacamento do vidrado em azulejos constitui a degradação última, uma vez que conduz à perda da camada vítrea que constitui o suporte do conteúdo pictórico. Esta degradação é geralmente considerada de uma maneira difusa, dizendo-se que o vidrado está em perda ou em destacamento. Essa foi a abordagem seguida ao preparar um vocabulário da degradação dos azulejos, na definição de "vidrado em destacamento". No entanto mesmo uma observação superficial dos destacamentos do vidrado permite reconhecer tipos diversos, frequentemente relacionados com o craquelé, cujas morfologias mais comuns este artigo propõe sistematizar.