Unique wood ash Co-coloured glass tessera from mediaeval Madonna: Raman spectroscopic study of production technology

0574311 - ÚACH 2024 RIV GB eng J - Journal Article
Čermáková, Zdeňka - Hradil, David - Bezdička, Petr - Hradilová, J. - Pánová, K.
Unique wood ash Co-coloured glass tessera from mediaeval Madonna: Raman spectroscopic study of production technology.
Spectrochimica Acta Part A-Molecular and Biomolecular Spectroscopy. Roč. 303, DEC (2023), č. článku 123183. ISSN 1386-1425. E-ISSN 1873-3557
R&D Projects: GA ČR(CZ) GA22-17966S
Institutional support: RVO:61388980
Keywords : Production Technology * Pseudowollastonite * Raman Micro-Spectroscopy * Tessera * Wood Ash Glass
OECD category: Inorganic and nuclear chemistry
Impact factor: 4.4, year: 2022
Method of publishing: Limited access
https://doi.org/10.1016/j.saa.2023.123183

While the natron and plant ash glass tesserae may be found on places of importance across the former Roman and Byzantine empires, wood ash glass tesserae are scarce. This is the first time a wood ash glass tessera is studied in detail. It was part of a magnificent 8-metres tall statue of Madonna in Malbork, Poland, created at the end of the 14th century and destroyed at the end of World War Two. It was found to be coloured by cobalt with possible impact of copper, and opacified by Ca-phosphate. Processes previously described in sodium-rich glasses were observed also in the studied potassium-rich wood ash glass tessera, such as diffusion of the respective alkali metal into the Ca-phosphate grains. The elemental composition of the tessera indicates that it is original – mediaeval, from the area north of Alps. Two phases were identified for the first time, to authors’ best knowledge, in any glass tessera – leucite (tetragonal KAlSi2O6) and pseudowollastonite (monoclinic CaSiO3). As pseudowollastonite is a high-temperature phase, it may serve as an indicator of production temperature, which was further supported by the study of polymerisation index of model glasses. This study contributes to the knowledge of old technologies and showed that the know-how for opacification was imported from the Mediterranean, while the raw materials employed for the base glass preparation were from the area north of Alps.
Permanent Link: https://hdl.handle.net/11104/0344653