Non-destructive composition analysis of glass artefacts for precaution

Chemical composition analysis on historical objects of art and archaeology assists in clarifying their authenticity and provenience. In addition, special technologies of their manufacture can be elucidated. Knowledge on the chemical composition represents one of the fundamentals for conservation and preservation concepts for historic silicate materials. The ensemble of ion beam analytical techniques (IBA) using external beams is a tool if non-destructive investigation is required.
Glass corrosion caused by environmental attacks is a serious problem especially for valuable historic objects. This is because the glasses may lose their transparency and stability. Alterations proceeding on the glass surface include ion exchange processes where network modifiers such as potassium and calcium are replaced by hydrogen bearing species to form a hydrated silica-rich surface layer. In order to characterise the state of a glass object showing no visible effects of alteration or corrosion damage, three ion beam based techniques (PIXE, PIGE, RBS) are combined in simultaneous measurements at the Rossendorf external proton beam. Combining PIXE (Proton Induced X-ray Emission) and PIGE (Proton Induced Gamma-ray Emission) the yield of X- and g-radiation of the element Si is ideal to indicate thin leached layers. More extended regions can be characterised by external RBS (Rutherford Backscattering Spectrometry). For getting the composition of the glass bulk the PIXE spectra are treated using the GUPIX code taking into account the experimental findings about the surface corrosion state. The developed procedure allows evaluation of initial corrosion and the identification of glass materials which are sensitive to atmospheric corrosion processes. The analytical results may offer suggestions for storing sensitive glass objects under special atmospheric conditions.
The present contribution demonstrates the applicability and the advantages of IBA techniques by investigating three medieval glass beakers.