Composition and colouring agents of historical Islamic glazes measured with EPMA and μ-XRD2
Gradmann, Rena; Berthold, Christoph; Schüssler, Ulrich
European Journal of Mineralogy Volume 27 Number 3 (2015), p. 325 - 335
published: Jun 1, 2015
ArtNo. ESP147052703006, Price: 29.00 €
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-XRD2). 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 SiO2, Al2O3 and K2O, but only for quartz frit substrates. PbO and/or alkali oxides were used as fluxes. Na2O is the dominant oxide in the alkali flux. MgO and P2O5 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 13th century in Iran, latest during the 13th/14th century in Afghanistan, and during the 14th/15th 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 Co2+ (blue), Cu2+ (green in a Pb-rich matrix), Fe3+ and Mn4+ (brown/black) and Mn3+ (violet). Pigments, such as SnO2, SiO2 and PbSiO4, are whitening agents; Pb2Sn2O6 was used for yellow colours. Iron-containing clinopyroxenes and Cu-Cr-Mn-oxides are found in black glazes.