Use of Hydrogen Isotopes to Understand Stained Glass Weathering

In order to assess the kinetic role of the alteration layers formed on stained glass windows weathered for several centuries, a specific experiment was designed. An ancient stained glass sample was subjected to an artificial simulated fog doped in deuteriumfor 13 weeks. The aim was to trace the circulation of water through the alteration layerand to locate reactive zones. Results demonstrate that the solution rapidly circulates in the alteration layer via pores and cracks, so that transport (especially the supply of protons at the interface between pristine and altered glass) is not rate-limiting in the alteration process. The alteration is rather controlled by the release of glass alkalis from ion exchange with protons at an estimated diffusion rate, consistent with the long-term apparent kinetics measured on medieval stained glasses.