Glass objects are common in shipwrecks since they are associated with ordinary glassware or commercial products. The alteration pathologies of historical glasses from two wrecks from the Mediterranean Sea were analyzed to characterize their alteration mechanisms. The results of this research proved that the alteration layers presented a moderate content of Na2O, similar to the average salinity of the ocean, and a high content of Al2O3 due to an extremely basic environment during the corrosion process. The biofouling layer protected the glass surfaces. Dark deposits with a high content of MnO were observed in the most instable glass.

The Cathedral of León has one of the most important ensembles of medieval stained glass windows in Europe; however, most of them have been altered by atmospheric weathering. The main objective of this study was the characterization of a set of glass samples from the Cathedral of León, the comparison with glasses from previous interventions in the cathedral and the study of the relation between the alteration pathologies, the chemical composition of the glasses and the environment in which they were placed. The samples were characterized by means of binocular microscopy, scanning electron microscopy and energy dispersive X-ray spectrometry, visible spectrophotometry, X-ray fluorescence spectrometry and X-ray diffraction. The main alteration of glasses exposed until the 19th century was the formation of pits by dealkalinization, while the glasses exposed until the present formed CaSO4 deposits as a consequence of the synergic effect of rainwater and gaseous pollutants. Glasses altered by the browning of manganese were also characterized. Resumen La Catedral de León posee una de las colecciones de vidrieras medievales más importantes de Europa; sin embargo, muchos de los vidrios se han alterado por degradación atmosférica. El objetivo principal de este estudio fue la caracterización de un conjunto de vidrios procedentes de la Catedral de León, su comparación con vidrios procedentes de intervenciones previas en la catedral y el estudio de la relación entre las patologías de alteración, la composición química del vidrio y el medio en el que estuvieron expuestas. Las muestras se caracterizaron mediante lupa binocular, microscopía electrónica de barrido y microanálisis de dispersión de energía de rayos X, espectrofotometría visible, espectrometría de fluorescencia de rayos X y difracción de rayos X. La alteración principal de los vidrios expuestos hasta el s. xix consistió en la formación de picaduras por desalcalinización, mientras que en los vidrios expuestos hasta la actualidad se formaron depósitos de CaSO4 como consecuencia del efecto sinérgico de la lluvia y los gases contaminantes. También se han caracterizado vidrios alterados por el enmarronamiento del manganeso.