Islamic and Hispano-Moresque (mfdejar) lead glazes in Spain: a technical approach

Abstract: Islamic and Hispano-Moresque glazes from the 10th to 15th centuries found in various archaeological sites, most of them workshops, are studied to show the technical evolution of the medieval glazing process. The technology seems to show a simplification: the early Islamic glazes were applied on prefired bodies and after fritting a lead-silica mixture, whereas for the later Islamic productions the raw materials for the lead glazes were not fritted and they were applied over unfired bodies. The same simplified technology was used in the Hispano-Moresque workshops. In the Islamic workshops lead glazes were coloured by adding elements (Fe, Cu, Mn), whereas the mfidejar technology simplified the process by using only one recipe to produce pots ofdifferent colour. This was achieved by applying the glaze in a different manner (on one side of the pot to obtain yellow or on both sides to btain green), or using different pastes (already used to produce pottery for different uses). Finally, there are differences between Islamic and Hispano-Moresque tin glazes related to the crystal size of the opacifier (tin oxide crystals), which should indicate some technological differences in temperature, glaze composition and the process to obtain the frits because of the high dependence b tween viscosity, temperature and crystal nucleatio