Investigations into structure and composition of gel layers on medieval window glasses of the Katharinenkirche, Oppenheim (Germany), and the Cathedral St. Gatien, Tours (France)

Abstract

Optical microscopy, Scanning Electron Microscopy (SEM), X-Ray Diffraction analysis (XRD) and Energy dispersive electron Probe Micro Analysis (EPMA) were used to characterize surface and subsurface layers and areas on medieval church window glasses generated by weathering and contamination, respectively. Investigations were carried out at surfaces and at existing or at artificially created cross-sections as well. Altogether 30 samples (22 from the Katharinenkirche, Oppenheim (Germany), and eight from the Cathedral St. Gatien, Tours (France)) were at disposal for the investigations. Depending on possibilities, conceded by the decisions of the responsible curators of the named historical monuments, investigations were carried out to get as much information as possible about chemical and structural characteristics of defects of the authentic glasses caused by weathering processes. In case of their appearance and detectability so-called gel layers or gel areas were of special interest. With attention to the specific conditions, samples were characterized with respect to the documentation of topographic changes of their surfaces (SEM), the detection and characterization of crystalline phases (XDA), the determination of compositions of the genuine glasses as well as material areas caused by weathering (EPMA). Using records of element-specific mappings, information about depth-dependent element distribution profiles was accessible.