Composition and colouring agents of historical Islamic glazes measured with EPMA and μ-XRD2

Abstract

Glazes from tiles of representative historic Islamic buildings and tableware ceramic from Central Asia, the Middle East, Asia Minor and North Africa were analysed by electron probe microanalysis (EPMA) and two-dimensional micro-X-ray powder diffraction (μ-XRD 2 ). From major element compositions, three main glaze types were identified: alkali, alkali–lead and lead glazes. Quartz frit and clay ceramics form the substrates of the glazes. A slight influence of the ceramic on the glaze compositions can be found for SiO 2 , Al 2 O 3 and K 2 O, but only for quartz frit substrates. PbO and/or alkali oxides were used as fluxes. Na 2 O is the dominant oxide in the alkali flux. MgO and P 2 O 5 are the decisive components for the discrimination between mineral soda and plant ash as a source of the alkali flux. The use of plant ash beside the established mineral soda as flux for the glazes was introduced during the 13 th century in Iran, latest during the 13 th /14 th century in Afghanistan, and during the 14 th /15 th century in Uzbekistan. Hence, a change of the flux happened later for the glazes than for local glass of the same regions. Lead-glaze compositions occur in almost all considered epochs and locations. Colouring ions are Co 2+ (blue), Cu 2+ (green in a Pb-rich matrix), Fe 3+ and Mn 4+ (brown/black) and Mn 3+ (violet). Pigments, such as SnO 2 , SiO 2 and PbSiO 4 , are whitening agents; Pb 2 Sn 2 O 6 was used for yellow colours. Iron-containing clinopyroxenes and Cu-Cr-Mn-oxides are found in black glazes.