Karolína Pánová finished her MSc. degree in the programme of Technology of Conservation and Restoration at the University of Chemistry and Technology in Prague in 2017. Since the beginning of her studies, she has focused on archaeological objects made from glass and ceramics and after graduation decided to pursue her research on the UCT Prague further. She is now a first year PhD student of the programme Chemistry and Technology of Inorganic Materials and her research focuses mainly on Czech historical glasses from 13th to 18th centuries, their composition, raw materials and technology of production, trying to connect the scientific and artistic approach to the subject of glass history.
Corrosion manifestation on model historical glasses in comparison with archaeological finds
Karolína Pánová*1, Dana Rohanová1, Dagmar Galusková2, Hana Kaňková2
1Department of Glass and Ceramics, Faculty of Chemical Technology, University of Chemistry and Technology, Prague, Technická 5, 166 28 Praha, Czech Republic
2FunGlass – Centre for Functional and Surface Functionalized Glass, Alexander Dubček University of Trenčín, Študentská 2, 911 50 Trenčín, Slovakia
Corrosion of glass is a complex process that has been studied and described for many years now and its understanding is important not only for the development of modern materials but for conservation and restoration of historical glasses as well. Various corrosion manifestations are present on almost all archaeological glass finds, from only a slightly matted surface to iridescent layers, pitting and sometimes even the total destruction of the object. Glass corrosion is generally more severe on central European potassium glass made with wood (beech, spruce or bracken) ash and wood ash potash than on southern European sodium glass, where the high sodium content originates from either ash of halophytic plants or sodium carbonate in the form of natron.
Systematic glass production in Bohemia began at the end of the 14th century and has been active since then. The composition of Bohemian glasses (until the 19th century) has always been potassium-calcium-silica.
Using a large number of analyses of Czech archaeological glasses, we were able to calculate their batches using natural raw materials – sand and/or quartz, beech ash, beech ash potash, limestone and some other minor components used for refining or decolourization of glass. These materials correspond tightly with the ones used in history. The calculations were carried out for the most significant glass types of three different historical periods – 14th century green “forest” glass (mainly known in the form of high and slender flute glasses “of Czech type”), 16th century pale green, almost colourless glass (goblets and beakers mimicking Venetian patterns) and late 17th century so-called crystal glass (lead-free Czech crystal glass mainly decorated by cutting).
These model glasses were then prepared and used as subjects for chemical durability tests and long-term experiments of glass corrosion. The samples were then examined by optical microscopy, X-Ray fluorescence analysis, SEM-EDS and ICP-OES analyses to determine the composition of the corroded layer on the surface and the amount and diffusion rates of leached alkalis.
We were able to compare the results with many real archaeological finds of Czech glasses of the three different compositions to better understand the corrosion process of Czech potassium-calcium glasses.
Figure 1. An example of pitting on historical glass (optical microscopy)
Figure 2. Iridescent layers on the surface of glass (optical microscopy)