A technological study on the 17th century raised gilded substrates in three royal palaces of Isfahan, Iran

The raised substrates of gilding decorations, called lāyachīnīī in Persian, were widely used throughout the Safavid period (1501-1736 AD) in Iran. This paper presents the first analytical data obtained from the lāyachīnīs of three seventeenth century royal Safavid buildings (ʿAlī- Qāpū, Chihil-Sutūn, and Hasht-Bihisht) in Isfahan, Iran, using energy dispersive X-ray spectroscopy, scanning electron microscope, Xray powder diffraction, and thin layer chromatography. According to the analytical data, different forms of calcium sulfate (dihydrate, β-hemihydrate, and anhydrite), the red iron oxides, and a proteinaceous binder (probably animal glue) are the main constituents of the raised lāyachīnī substrates. The results show that a dry mixture of the plaster of Paris and the red iron oxides are mixed with diluted animal glue to obtain a slurry to be applied in several layers, one top of the another, to achieve the raised substrates. This technique is similar to those European raised pastiglia substrates although the method of the preparation in the Persian technique is different from the European one.