Evolución del color en el alero de la fachada del rey D. Pedro I, Real Alcázar de Sevilla. Aportaciones del estudio de materiales a la identificación de las intervenciones de restauración a lo largo de su historia

Results from the research carried out on the polychrome decoration of the fa ade of the King Pedro I Palace, which was built as part of the Alcázar of Seville between 1356 and 1366, are here explained. This building is regarded as one of the most important examples of architecture from al-Andalus in the Iberian Peninsula. The polychromy of its fa ade has been subject to numerous interventions throughout its history, but its general appearance remains largely unchanged, variations can be observed in details though. The predominant finishing has always been golden, on a background of reds, blues and greens. After an accuracy painstaking and sampling fieldwork, various laboratory techniques were brought together to identify and study the inorganic and organic phases that comprise the pictorial layers. Such techniques include optical microscopy with reflected and transmitted light, X-rays powder diffraction, scanning electron microscopy with EDX microanalysis, gas chromatography and high pressure liquid chromatography. At least eight polychrome decorations have been identified, corresponding to different levels carried out in different epochs. Each decoration has usually several layers: preparatory, base, and pictorial or golden foil layer, being the latter the most commonly used as finishing layer. The decorations use a wide variety of pigments: red lead, cinnabar/vermilion, lead white, natural and synthetic azurite, synthetic ultramarine, malachite, emerald green, As-Cu green, lead-tin yellow, chrome yellow, yellow litharge, and organic black. Detailed study of the textures and the precise characterization of the pigments used on the fa ade have enabled the successive interventions to be dated and their spatial correlation to be identified. Regarding the original pigments, remains of lead red and cinnabar were found, followed by layers of cinnabar/vermilion, azurite and malachite, these of natural origin. It was identified that in those decorations dated between the 16th and 18th century cinnabar is replaced by vermilion, and natural azurite is replaced by its synthetic equivalent. More recent interventions reveal that the most widely-used pigment is emerald green (synthesised from 1814 onwards), this constituting a reference level. From the late 19th century onwards, some emerald greens and synthetic azurite blues are replaced by synthetic ultramarine. Se presenta la investigación realizada en la policromía de la fachada del Palacio de Pedro I, edificio construido en los Reales Alcázares de Sevilla, entre 1356 y 1366, que constituye una de las obras más i