Innovative techniques for the characterisation of encrustation on Pentelic marble from the Parthenon

Abstract

Discusses how patina samples from black incrustations found on the Pentelic marble from the Parthenon are characterised using different analytical techniques such as optical microscopy, scanning electron microscope coupled with energy dispersive X-ray (SEM-EDX) analysis, laser induced breakdown spectroscopy (LIBS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and a novel hyper-spectral imaging (HySI) analysis for the characterization of coloured samples. SEM-EDX and LIBS measurements helped identify two main alteration layers. The external layer was mainly composed of alumino-silicates, gypsum, and particulates, while the internal layers had a more homogeneous distribution of sulphur with limited quantities of iron (II), silicon and aluminium. LIBS is shown to be an effective in situ instrument for revealing stratigraphic trends in the emissions of the elements found in black crusts. Using the results obtained from these measurements and historical documentation, the chemical and physical nature of these patinas and previous protective or aesthetic treatments applied on the marble, specifically alkali silicates, were identified. A table containing the results of the quantitative analysis of the black incrustation is provided.