Pigments and plasters from the Roman temple of Deir El-Hagar, Dakhla Oasis, Egypt: vibrational spectroscopic characterization

Abstract

Deir El-Hagar temple at the Dakhla Oasis of the Western desert is a rare example of the surviving complete Roman structures in Egypt. The temple was discovered in 1819, and since that date, several restoration attempts have been carried out for its preservation. In the present case study, pigment and plaster samples from Deir El-Hagar temple were analyzed, for the first time, using different analytical methods. Initially, the microscopic observations were applied to collect stratigraphic data on the pictorial layers and the appropriate areas for analysis. The vibrational characteristics of the contained mineral phases were determined using Raman microspectroscopy. The surface morphology and microfeatures of the samples were accomplished by an environmental scanning electron microscopy and the energy-dispersive X-ray micro-analyzer (SEM–EDAX). Additionally, the visible reflectance spectroscopy (vis-RS) was used as a complementary method to record the reflectance spectra of some pigment samples. As such, the analytical techniques used in this study allowed the identification of the vibrational spectroscopic characteristics and the mineralogical–chemical composition of the studied samples. The results showed that the temple walls were plastered with two layers, coarse plaster and thin whitewash render. The blue pigment sample was identified as Egyptian blue and the occurrence of arsenic-based compounds in the sample was also reported and discussed. It was confirmed that a heated goethite, rather than natural red ochre, was used to produce the red colour. Additionally, mixed pigments were used to produce different hues and tonalities. A charcoal black, most likely of a charred wood, was used as a black pigment. Moreover, several proportions of haematite and magnetite were detected along the scanned surface of the black pigment. The findings of the current research allowed delivering an analytical report on the painting materials used in an important example of the Roman monuments in the Western desert of Egypt.