Potassium-rich ash-based glass is typical of medieval glass windows used in the Central Europe since 1000 A. D.. Glasses with medieval-like composition were prepared with different amounts of K2O (15–20–25 K2O weight%) using recipes deduced from archaeometric literature. Raman data of these samples were interpreted on the basis of the Qn units model and of the polymerization index Ip and confirm a close dependence of glass depolymerization on the potassium content. Generally, K-based glasses have high alteration sensitivity to pollutants conveyed by liquid or vapour water (rain, humidity and fog). In this work, the glass alteration processes were studied in terms of structural modifications related to the glass K content. Leaching and network dissolution were investigated by attack with boiling concentrated sulfuric acid and by exposure to high temperature and high pressure bidistilled water, respectively. The weight loss and alteration layer thickness were measured. The structural changes in the glass network and the presence of neoformation crystallized products were determined through linear Raman maps on altered glass cross sections. The more the glass network structure is depolymerized, the more the surface chemical attack is facilitated. The results obtained for the model glasses are comparedwith those for a set of ancient K-rich glass fragments.
Raman study on medioeval-like glass samples: glass characterization, artificial weathering and comparison with ancient K-based glasses / De Ferri, L.; Bersani, D.; Colomban, P. h.; Lottici, P. P.; Simon, G.; Vezzalini, Maria Giovanna. - STAMPA. - 1:(2011), pp. 28-28. (Intervento presentato al convegno 6th International Congress on the Application of Raman Spectroscopy in Art and Archaelogy tenutosi a Parma nel 5-8 September 2011).
Raman study on medioeval-like glass samples: glass characterization, artificial weathering and comparison with ancient K-based glasses
VEZZALINI, Maria Giovanna
2011
Abstract
Potassium-rich ash-based glass is typical of medieval glass windows used in the Central Europe since 1000 A. D.. Glasses with medieval-like composition were prepared with different amounts of K2O (15–20–25 K2O weight%) using recipes deduced from archaeometric literature. Raman data of these samples were interpreted on the basis of the Qn units model and of the polymerization index Ip and confirm a close dependence of glass depolymerization on the potassium content. Generally, K-based glasses have high alteration sensitivity to pollutants conveyed by liquid or vapour water (rain, humidity and fog). In this work, the glass alteration processes were studied in terms of structural modifications related to the glass K content. Leaching and network dissolution were investigated by attack with boiling concentrated sulfuric acid and by exposure to high temperature and high pressure bidistilled water, respectively. The weight loss and alteration layer thickness were measured. The structural changes in the glass network and the presence of neoformation crystallized products were determined through linear Raman maps on altered glass cross sections. The more the glass network structure is depolymerized, the more the surface chemical attack is facilitated. The results obtained for the model glasses are comparedwith those for a set of ancient K-rich glass fragments.Pubblicazioni consigliate
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