Micro-Raman spectroscopy and X-ray fluorescence spectrometry on the characterization of the Persian pigments used in the pre-seventeenth century wall paintings of Masjid-i Jāme of Abarqū, central Iran

Abstract

The pigments used in the wall paintings of the Masjid-i Jāme of Abarqū, central Iran, as less-known pigments used in the history of Persian painting, were investigated with micro-Raman spectroscopy, micro X-ray fluorescence (micro-XRF), scanning electron microscopy (SEM), and polarised light microscopy (PLM). The results showed that the green, red, and blue pigments were atacamite, red lead, and smalt mixed with natural ultramarine blue respectively applied on a white substrate composed of white huntite. Moreover, the blue smalt was identified to be used on the white huntite and under the paint layer in order to delineate the design of the wall paintings and to act as a rough sketch for the subsequent use of the other pigments. Glushinskite, as a less-reported mineral in historical wall paintings, was identified by micro-Raman spectroscopy and hypothesised to be associated with the degradation of the white huntite binder. Furthermore, micro-Raman spectroscopy studies surprisingly revealed the mineral woodhouseite sparely mixed with the green pigment. This paper strongly suggests micro-Raman spectroscopy for identifying archaeological pigments and for diagnosing their deterioration products. Conducting scientific methods of analysis, the pigments identified in this study are reported for the first time to be used in Persian wall paintings.

Keywords: Atacamite; Huntite; Masjid-i Jāme of Abarqū; Micro-Raman spectroscopy; Micro-XRF; Smalt.