ABSTRACT
ABSTRACT: Samples of Pentelic marble from theAcropolis inAthens covered with encrustation have been studied with the aid of several analytical techniques in order to identify the alteration products. The encrustation examined is formed on the marbles: (a) as products of the interaction between the stone surface and atmospheric pollutants (black crusts, >200µm), (b) from treatments conducted in the past for aesthetic and/or protective purposes (orange-brown patina in Parthenon, 100-150µm thick) and (c) from a brown plaster on the Erechtheion consisting of lime, siliceous sand and inorganic earth pigments (∼100µm thick). Elemental in-depth profiles of polished sections of samples have been obtained by means of a scanning electron microscope coupled with energy dispersive x-ray analysis (SEM-EDS) and the laser induced breakdown spectroscopy (LIBS). A novel Hyper-spectral imaging (HySI) system, capable of acquiring images in the spectral range 380-1000 nm has also been employed for the non-destructive characterization of the colored samples. X-ray diffraction (XRD) and infrared spectroscopic studies (FTIR) reveal calcium oxalates only in the Parthenon patinas. In the black crusts, the S, Fe, Si and Al SEM-EDS and LIBS profiles exhibit a significant decrease with depth, thus expressing decreasing contamination within the alteration layers, since these elements originate from atmospheric pollution and deposition. The patina samples show homogeneous distribution of Fe, Si and Al both in the chromatic layer and inside (up to a depth of 300µm from the surface), implying that these elements originate from sources other than environmental loading. The combination of the results of the above-mentioned techniques together with the historical documentation from archives of the Committee for the Preservation of theAcropolis Monuments, leads to the conclusion that alkali silicates have been applied for the preservation of the Parthenon marbles in the past.
