An analytical approach to the glazed architectural decoration in Iran from the 12th to the 14th century

Architectural glazed elements in Iran during the Islamic period first appeared in the mid-11th century, featuring monochrome and cut tiles. By the 13th-14th centuries, a wide variety of tiles employing diverse techniques, such as lustre, lajvardina, monochrome and underglaze, were developed and reached their culmination in Iran. This level of diversity in tile-making techniques represents a high point in the history of tile-making in Iran. In this study, bodies and glazes from 140 glazed tiles collected from twenty-five monuments in Iran, dating back to the period from the 12th century to the 14th century, were studied by polarised light microscope (PLM), micro-X-ray fluorescence (µ-XRF), micro-Raman spectroscopy (µ-Raman) and scanning electron microscopy – energy dispersive X-ray spectrometry (SEM-EDS). We demonstrate that white, blue and turquoise are the dominant colours used in the palette of glaze-makers from the 12th up to the 14th century. We also suggest that no yellow lead-tin opacified glaze has been used as an architectural element in Iran in this period, and green, black and transparent yellow glaze were only rarely employed on the tiles. It is also observed that while turquoise and white glazes were mostly produced in lead-alkali glazes opacified with white SnO2 particles, the blue glazes were mainly lime-alkali in nature and rarely opacified and were thicker and smoother with respect to the other glazes. Moreover, a criterion based on the quartz content of the stonepaste bodies is suggested to distinguish the tiles produced in the 12th-century Saljuq bodies from those of the 13th-14th century Ilkhanid ones. In addition, we propose that glazes employed on clay-based bodies contained a Pb/Sn lower than those covering the stonepaste bodies, yielding a higher opacification needed to conceal the buff/red colour of the bodies. Furthermore, a rare cobalt mineral is reported to be responsible for the blue colour. These findings bring further implications for our understanding of Persianate medieval architectural heritage through lens of art and architectural historians.