Three sets of glass samples from 18th century leaded windows from the Girona Cathedral, Reus Priory Church and the Vitoria Cathedral (Spain) have been studied. Chemical analyses and archaeometry of these glasses are of special interest due to both the scarcity of 18th century stained glass window production and to the particular orange colour of several glass pieces. Chemical degradation of glasses has been deduced from their composition and conservation state, directly observed using optical and electron microscopy. The chemical species responsible for colouring (chromophores) and other chromatic parameters have been investigated from optical spectroscopic data. The results indicated that glasses from Girona Cathedral are potash-lime-silica glasses, whereas those of the Reus Priory Chruch and Vitoria Cathedral are soda-lime-silica glasses. The durability of the glasses studied is directly related to their respective chemical composition: potash glasses from Girona show advanced chemical degradation, compared with the other sets of glasses analysed.
