Alteration of medieval stained glass windows in atmospheric medium: review and simplified alteration model

Abstract

Abstract Stained glass windows are a precious heritage to pass on to future generations. However, medieval stained glass windows are particularly altered due to their chemical composition and the effects of climatic (mainly water and temperature), environmental (pollution) and biological factors. In this review, we present the alteration patterns observed on ancient Si-K-Ca stained glass windows. To better understand their formation mechanisms and determine the alteration rates, different exposure campaigns to the current atmosphere in a position sheltered from rain or not and laboratory experiments in aqueous medium or in gaseous phase have been conducted. Either model glass or ancient stained glass windows were studied. Isotopic tracers (D, 18O, 29Si) have been used as they constitute a powerful tool to elucidate the involved processes and to measure their kinetics. Thanks to all of these data, an alteration scenario of medieval stained glass alteration is proposed. Besides, the extrapolation of kinetic data based on several hypotheses over seven centuries gives very consistent results compared to the ancient stained glass samples.