Characterization of the mural blue paintings in ornamental motif of Ali Qapu palace in Isfahan, Iran, using spectroscopic and microscopic methods (a case study)

Abstract

This study aimed to investigate the painting technique and identify the blue pigments used in the ornamental motif of mural paintings of Ali Qapu palace as the seat of rule of Shah Abbas I Safavid and part of Naghsh-e Jahan square world heritage site in Isfahan. For this investigation, five samples collected from the murals located at different sections of the palace were studied by polarized light microscopy (PLM), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and energy-dispersive X-ray spectroscopy (EDS). Also, the Fourier self-deconvolution was applied to the FTIR spectra of chloroform extract of the paint layer to identify the type of binder used in the painting. The results showed that the blue pigment used in all five samples is natural ultramarine (lapis lazuli). In four of the five samples, huntite has been used as the filler in the priming layer. However, the results suggest that huntite has also been combined with ultramarine to create lighter tonalities. The findings indicate the use of three different priming methods in creating the ornamental motif murals: creating a priming layer with iron-rich soil, creating a priming layer with huntite as the filler, and placing an organic layer underneath the huntite priming layer. This shows the variety of priming techniques used in creating the ornamental motif murals of Ali Qapu. Furthermore, FTIR results indicate the possible use of the tempera and oil technique in the murals.