Influence of the production technology on the morphological characteristics of azulejos

Abstract

In this article some aspects of the production technology connected with the preparation of the glaze and of the biscuit and with the firing cycle have been researched in order to better understand their effects on the morphological and chemical characteristics of the glaze and glaze-biscuit interface. Azulejo reproductions have been prepared by using raw and fired ceramic bodies glazed with either a lead-tin raw preparation or with a frit of different quartz grain sizes. The firing temperatures and the duration of the firing cycles have also been varied. The resulting cross-sections of the ceramic reproductions were analyzed with SEM-EDS. An increase in the Pb enriched K-feldspars formed at the glaze-biscuit interface is observed as the maximum temperature increases and the cooling rate slows. The use of raw glazes and single firings also promotes the growth. The results led to a better interpretation of the technological fingerprint observed on historic glazed tiles and offer more insight into the early azulejo production technologies and on the nature of the glaze-ceramic interface.