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In a recent study, a team of researchers used Raman spectroscopy to study wood ash glass tessera from Malbork Madonna, revealing two phases detected in tessera for the first time, leucite and pseudowollastonite.
In a new study published in the journal Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, a team of five researchers led by Zdeňka Čermáková (along with David Hradil, Petr Bezdička, Janka Hradilová, and Karolína Pánová) used Raman spectroscopy to better understand medieval art and craftsmanship (1). The study examined unique wood ash glass tessera that once adorned an eight-meter-tall statue of Madonna in Malbork, Poland, which was created at the end of the 14th century and subsequently destroyed during World War II (1).
Glass tesserae, often composed of natron and plant ash glass, have been discovered at historical sites across the former Roman and Byzantine empires. However, wood ash glass tesserae have been rare finds in the archaeological record. This research marks the first in-depth analysis of a wood ash glass tessera, shedding light on its production technology and origin (1).
The study reveals that the wood ash glass tessera was colored using cobalt, with a potential influence of copper, and opacified with calcium phosphate derived from burnt and powdered bones. Notably, the elemental composition of the tessera indicates its authenticity as a medieval artifact from the region north of the Swiss Alps. This finding offers a glimpse into the artistic practices and materials used during this period (1).
One of the most remarkable discoveries in this study is the identification of two phases in the glass tessera, leucite (tetragonal KAlSi2O6), and pseudowollastonite (monoclinic CaSiO3). Pseudowollastonite, a high-temperature phase, serves as an indicator of the temperature achieved during tessera production. The research also involved an analysis of the polymerization index of model glasses, further supporting the conclusions about production temperature (1).
This study provides valuable insights into historical glassmaking techniques and the cross-cultural exchange of knowledge. The findings suggest that the knowledge for opacification, such as the use of Ca-phosphate, was likely imported from the Mediterranean. However, the raw materials for the base glass preparation came from the region north of the Alps, highlighting the complex and interconnected nature of medieval craftsmanship (1).
The blue wood ash glass tessera from the Malbork Madonna has drawn attention because of its unique properties and composition. It stands as a testament to the artistic and technical achievements of the medieval era, and this study opens a window into understanding the ancient craftsmanship that created such awe-inspiring works of art (1).
In conclusion, the Raman spectroscopic study of wood ash glass tessera offers a glimpse into the historical and artistic past of Europe, enriching our knowledge of medieval production technologies and artistic practices. The research not only uncovers the secrets behind the colors and opacification of this magnificent glass tessera, but also highlights the intricate craftsmanship that has left its mark on history.
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(1) Čermáková, Z.; Hradil, D.; Bezdička, P.; Hradilová, J.; Pánová, K. Unique wood ash Co-coloured glass tessera from mediaeval Madonna: Raman spectroscopic study of production technology. Spectrochimica Acta Part A: Mol. Biomol. Spectrosc. 2023, 303, 123183. DOI: 10.1016/j.saa.2023.123183