Application of surface science techniques to study a gilded Egyptian funerary mask: A multi-analytical approach

A wide range of analytical techniques has been used to study an Egyptian funerary mask of the Ptolemaic period (305-30 bc). Secondary electron (SE) and back-scattering (BS) images, recorded by a scanning electron microscope (SEM), provided a detailed representation of the metallurgical techniques used to construct the gilded mask. It is confirmed, that the golden leaf used to cover the mask is the product of an antique refinery practice, so called, cementation process of naturally occurring alloy of gold and silver, namely electrum. Complementary results of SEM-electron dispersion spectroscopy (EDS) and electron probe microanalysis (EPMA)-wavelength dispersion spectroscopy (WDS) provided chemical compositions of the golden leaf as well as in the plaster base of the mask. X-ray photoemission spectroscopy (XPS) revealed the presence of Au, Ag, Si, S, Cl, Ca, and N, in addition to O and C. Relative concentration of Au/Ag at the surface has been measured by XPS to be 70% to 30%. XPS depth profiling verified silver-enrichment at the surface, as ratio of gold to silver is measured to be 80% to 20% at the depth of 15 nm. XPS chemical mapping images of gold and silver confirmed a rather inhomogeneous character of Au/Ag relative concentration at the surface. The main diffraction peaks in the X-ray diffraction (XRD) spectrum coincide with diffraction peaks of pure gold, silver metals, and magnesium calcite Mg0.03Ca0.97CO3. Whereas, Raman spectroscopy results implied the existence of Ag2S, a tarnishing compound, on the golden area of the mask.