Haft rang or cuerda seca? Spectroscopic approaches to the study of overglaze polychrome tiles from seventeenth century Persia

Seventeenth century polychrome overglaze haft rang tiles found in various regions of Iran (Isfahan, Qazvin, Mashhad, and Mazandaran) were investigated with ultravioletevisible spectroscopy (UVeVis), portable X-ray fluorescence (pXRF), energy dispersive X-ray spectroscopy (EDS), and micro-Raman spectroscopy. Two types of glazes were identified, namely low lead-alkali and high lead glazes, in which cobalt, copper, iron, and manganese were used as colourants. Tin oxide and lead-tin yellow were recognised as white and yellow opacifiers respectively. The black line, which was used for delineating the tiles’ design, was mainly composed of manganese, iron, and aluminium oxides. The high maturing temperature of this line prevented the low-temperature coloured glazes run together during the firing. Finally, technological differences between haft rang and cuerda seca techniques are highlighted and minai overglazes are briefly compared with haft rang overglazes.