Archaeometric case-study of tiles of different dates from the Royal Monastery of San Lorenzo de El Escorial (Spain)

Abstract With the aim to contrast existing historical documentation with information provided by the own materials, an archeometric study of a representative set of tiles from the Monastery of El Escorial was undertaken. The ensemble, composed of 19 ceramic fragments, covers examples from the 16th and 17th century, either from Talavera or Toledo provenances, and was selected according to stylistic criteria. The goals of the study consisted in determining the average chemical composition of the ceramic body, its textural and microstructural characteristics, the crystalline phases to establish firing temperatures, also in studying these aspects in the enamel or glaze layer, as well as in identifying the chromophores for the coloring of the decorations. Conventional techniques such as binocular magnifying glass, XRF spectrometry, petrographic observation by thin-section, XRD, FESEM with EDS microanalysis and visible spectrophotometry were used. Resulting data indicated the use of calcareous clays for the body (22.0–25.5 wt.% CaO), the presence of neoformed phases such as gehlenite, diopside and anortite which suggest a firing temperature between 950 and 1050 °C approximately, lead-based glazes (∼25.0 wt.% PbO on average) with SnO2-opacifier (∼57.0 wt.% on average) and Co2+, Cu2+, Fe3+-ions and lead antimoniate for blue, green, brown and yellow decorative colors, respectively.