Judit Molera has been invited as keynote speaker in the frame of the online event WAITINGFOREMAC2023@Pisa which will take place on July 6-8, 2021
(http://www.emac2023.it).

Crystalline phases inside glazes as a fingerprint of ceramic technology

Keynote on Waiting for EMAC 2023, 6th July 2021

A glaze is a thin glassy layer fused to the surface of a ceramic that could have bubbles, cracks and crystalline phases. Unreacted grains may remain in glazes revealing the raw materials used. Half-reacted components and newly formed crystals during firing are fingerprints of kiln temperature and firing conditions. All of them are tracers of the technology of glazed ceramics and their study makes it possible to contribute to the historical knowledge of ceramics1.

This conference reviews the main characteristics of lead glazes and how they have evolved over the centuries. In the first place, it will be presented what transformations occur during the firing in lead glazes depending on whether lead oxide or galena (lead sulfide)2 is used and the transformations when adding tin to obtain the white glazes. Case studies will be exposed that range from medieval pottery, made with lead compounds previously fritted, to 18th century pottery made with galena and quartz sand. Secondly, it will be seen what degree of interaction between the paste and the glaze according to the type of firing (single firing or double firing), temperature, composition and thickness of the glazing. The crystals that develop in the pasta-glass contact are a good indicator of the cooking technique. Finally, the study of the pigment remains and newly formed crystals of manganese, iron and cobalt³ decorations will be presented. Evolutions of crystals phases formed during were investigated through High Temperature X-ray diffraction using synchrotron radiation (HT-XRD). Crystals were also identified in thin section by optical microscopy (OM) and scanning electron microscopy (SEM).

 

References

1. Pradell, T. & Molera, J. Ceramic technology. How to characterise ceramic glazes. Archaeological and Anthropological Sciences; 12 8, (2020). 8p.
2. Di Febo, R., Molera, J., Pradell, T., Melgarejo, J.C., Madrenas, J., Vallcorba, O. The production of a lead glaze with galena: Thermal transformations in the PbS–SiO₂ Journal of the American Ceramic Society, 101, (2017), 2119-2129.
3. Molera, J., Climent-Font, A., Garcia, G., Pradell, T., Vallcorba, O., & Zucchiatti, A. (2021). Experimental study of historical processing of cobalt arsenide ore for colouring glazes (15-16th century Europe). Journal of Archaeological Science: Reports, 36. April 2021, 102797