For several centuries, the external and internal surfaces of mediaeval stained glass windows are continuously exposed to water (rain events, humidity, condensation/dry cycle), which causes the alteration of their external/internal surfaces. These conditions of high humidity also favours the development of microorganisms. Due to their composition, medieval glasses can be attractive substrates for the development of biofilms, as they represent a source of nutrients for microorganisms . However, due to the multitude of parameters involved, these interactions are not well understood and are still poorly documented.