Pedological stratification effect of corrosion and contamination products on Byzantine bronze artefacts

The present paper deals with the identification of six ancient Byzantine bronze coins found in the same archaeological site of Nufarul (Tulcea County, Romania), by corrosion product and alloy analysis. The microstratigraphies (i.e. layers), together with microchemical tests including reflection colorimetry, IR spectroscopy, X-ray diffraction and scanning electron microscopy assisted by X-ray spectrometry have rendered evident the stratified morphology of three types of patina. They are the primary type resulting from redox processes, the secondary type determined by acid-base and related hydrolytic processes and the ternary type (or the contamination patina) from segregation, diffusion and osmosis processes. The stratigraphical distribution of the chemical components in the structure of the patina is caused by the pedological (soil) processes at the archaeological sites and can be the main factor used in the authentication of ancient bronze artefacts.