Reflections - Abstract - Ferdinand Drünert

Calcium antimonates as opacifying agents in historical glass samples -
remelting experiments and in situ crystallization
F. Drünert¹, D. Möncke¹, E. Palamara², N. Zacharias², L. Wondraczek¹

Glazes and glassy coatings of ceramics are known to mankind since the 5th ct. BCE. Often these glazes were opacified by microcrystalline particles like the antimonates CaSb₂O₆/Ca₂Sb₂O₇ (white) and Pb₂Sb₂O₇ (yellow), as we can see not only in glazes of different antique cultural spheres, but also in glass mosaic tesserae of the Roman period [see e.g. Shortland (2002), Lahlil (2010)]. According to the literature, the opacification of white glazes and mosaic tesserae is caused by two different antimonates. While the trigonal CaSb₂O₆ is found in glazes, mosaic tesserae are apparently opacified by the orthorhombic Ca₂Sb₂O₇. In this study, the influence of nucleating agents in a model glass composition on the formation of the trigonal resp. orthorhombic antimonate is shown.

In comparison of original samples with modern glasses of similar composition, this study investigates the influence of tin- and titanium oxide additives on the nucleation of microcrystalline antimonate particles. Thus, the focus lies on the different in-situ nucleation behavior in relation to temperature and glass composition, as well as the characterization of the different antimonate phases with Raman spectroscopy. It could be shown, that tin oxide leads to an increasing surface crystallization of trigonal CaSb₂O₆, whereas the crystallization of orthorhombic Ca₂Sb₂O₇ can be enhanced by addition of titanium oxide. Both oxides are common traces in historical glass samples.

Literature:

Lahlil S., Biron I., Cotte M., Susini J., "New insight on the in situ crystallization of calcium antimonate opacified glass during the Roman period', Appl. Phys. A 100 (2010), S. 683 - 692

Oikonomou Ar., Beltios K., Zacharias N., "Analytical and technological study of an ancient glass collection from Thebes, Greece: An overall assessment", Annales du 19e Congres del' Association Internationale pour l'Histoire du Verre, AIHV (2012)

Papageorgiou M., Zacharias N., Beltsios K., "Technological and typological investigation of late Roman glass mosaic tesserae from ancient Messene, Greece", Annales du 18e Congres del' Association Internationale pour l'Histoire du Verre, AIHV (2009)

Shortland A. J., "The use and origin of antimonate colorants in early Egyptian glass", Archaeometry 44 (2002), S. 517 - 530

Institutions:

1 Otto Schott Institute of Materials Science, Friedrich Schiller University Jena, Germany;

2 Laboratory of Archaeometry, University of the Peloponnese, Kalamata, Greece