A Fragile Heritage
Aspects of Historic Glass
Cambridge - Wednesday 6th September 2017



Gauthier Roisine
<gauthier.roisine@chimie-paristech.fr>

article posted 4 Apr 2017

Gauthier Roisine studied chemistry in the École normale supérieure in Paris where he developed interest in material sciences (Master of Physical-chemistry of materials).

He is carrying out research for his PhD in the Institut of Research of Chimie Paris (IRCP) and the Center of Research and Restoration of the Museums of France (C2RMF) under the direction of Daniel Caurant (IRCP) and Anne Bouquillon (C2RMF); "Glazes of Bernard Palissy : looking for the secrets of a master of Renaissance".


Crystallisation of iron coloured high lead glazes:
Looking for Bernard Palissy's secret (1510-1590)
G. Roisine*1,2, D. Caurant1, G. Wallez1,
A. Bouquillon2, O. Majérus1, L. Cormier 3

Bernard Palissy, a master potter of the French Renaissance, produced outstanding glazed ceramics decorated with remarkably vivid animals - called "rustiques figulines" (Fig. 1). Thanks to this ceramics, he was noticed by the court of France and was invited to continue his work in the jardin des Tuileries, in the Louvre.

He tells in his "Discours Admirables" the story of the invention of these remarkable ceramics and how much and hard he worked before finding the right glaze composition and firing conditions to elaborate his works of art. Naturally, he kept jealously secret their manufacture process . Nevertheless, we have today access to a unique archaeological material excavated from his workshop in the Louvre (1984-2003) , that gives us a chance to discover his manufacturing process through a replication and comparison approach. Moreover, the knowledge of his process could help to authenticate the numerous ceramics attributed to Bernard Palissy all over the world.

In this paper, we focus on the characterisation of yellow to brown transparent glazes, originating from Palissy's workshop or synthesized in laboratory. The analysis of 15 archaeological samples discovered in Palissy's Parisian workshop showed (SEM-EDS) indeed that he used a relatively stable recipe from one object to another: an iron coloured (3-5 wt% Fe2O3) high lead aluminosilicate glaze (55-65 wt% PbO, 5-7 wt% Al2O3, 26-32 wt% SiO2).

Replicate glazes were prepared in the laboratory in Pt crucibles from raw materials mixtures, with various iron carriers and fired at different temperatures Tp (750-1025°C) with various cooling rates (quenching/slow cooling). The characterization of these replicate glazes by SEM, XRD and Raman spectroscopy often showed a high crystallisation trend of iron-rich phases either during heating or cooling (Fig.2).

It appears that the nature of the crystalline phases formed in the glaze after firing (Fe2O3, Pb2Fe2Si2O9, PbFe12O19), their abundance and microstructure strongly depend on both Tp and cooling rate.

The comparison of the results obtained for replicate glazes with archaeological Palissy's glazes give us some clues on his process of manufacture: archaeological glazes are usually poorly crystallised (Fig. 3), indicating a high temperature of firing (~1000°C) and a rather fast cooling rate (faster than 5°C/h). To complete this work on the melting and crystallisation behaviour of raw materials mixtures, the crystallisation tendency of homogeneous glasses of similar composition but with increasing Fe2O3 content (0-10 wt%) as a function of the temperature will be also presented. Finally, in order to get closer to the whole ceramic system, the study of the interaction between of the glaze and the ceramic body is in progress.



Institutions:

1 Chimie ParisTech, PSL Research University, IRCP, 75005 Paris, France

2 C2RMF, Palais du Louvre, 75001 Paris, France

3 IMPMC, Sorbonne Universités, 75005 Paris, France