Modelling the Alteration of Medieval Stained Glass as a Function of Climate and Pollution: Comparison between Different Methodologies

Abstract

Most stained-glass windows installed during the Middle Ages have deteriorated over time due to climate and pollution. To reconstruct their alteration history over the centuries, evaluate the current environmental risk, and predict their alteration in the future, two modelling methodologies have been used. First, based on the short-term exposure of medieval-type glass in different sites, dose–response functions (DRFs) were established. These DRFs correlate relevant environmental factors (temperature, rain quantity, rain pH, relative humidity, and SO2 concentration) with the response of the material in terms of alteration layer thickness. The second methodology consists of laboratory experiments that aim at parametrising kinetic laws as a function of specific parameters (temperature, rain pH, and relative humidity). These kinetic laws can be extrapolated over long periods, contrary to DRFs. In this study, we compared both methodologies to simulate the alteration of a model stained glass at different European sites or over different time periods. The results highlighted that the kinetic laws were able to closely represent the data, except for the polluted sites where the alteration was underestimated. This indicated that the dependence of the alteration rate on the pollutant concentrations should be included to improve the model.