The stained glass window – both a work of art and a closing panel of the building – raises serious preservation issues, because of its fragility and its direct exposure to weather and air pollution. The LRMH works on all stained glass windows, and more particularly on medieval stained glass windows (the cathedrals of Tours, Chartres and Troyes, the Sainte-Chapelle in Paris, etc.).
The Chemical Composition of Stained Glass and Grisailles
There are two very good reasons for working on the chemical characterization of various different materials, glass samples and vitreous paint: research into technological markers and research into deterioration markers. In this collaborative work undertaken between the LRMH and the Research and Restoration Center for the Museums of France (C2RMF), quantitative analyses of glass and grisailles are performed using ion beams on the particle accelerator housed in the Louvre (known by its French acronym, AGLAE, for Accélérateur Grand Louvre d'Analyse Elémentaire). These methods deliver high sensitivity while remaining perfectly harmless for the heritage objects being examined and enable direct analysis of stained glass panels without requiring disassembly.
Mechanistic Analysis of Deterioration in Medieval Types of Glass
The aim of this research is to determine the corrosive mechanisms responsible for the physical-chemical deterioration of stained glass dating from the Middle Ages. By comparing a collection of early samples (fourteenth and nineteenth centuries) and glass displayed in situ, it is possible to correlate the phenomena and thus gain a better understanding of the chemical and physical processes at work within the glass matrix.
Browning Phenomenon of Stained Glass Windows
Because of contact with its surrounding environment, medieval glass containing potassium undergoes major chemical changes, resulting in impairment of the glass’s visual properties. In the specific case of glass containing upward of 0.1 wt% manganese oxide, used as a coloring or de-coloring agent in glassmaking since ancient times, browning of the glass can sometimes occur, ultimately leading to a complete loss of the glass’s transparency.
The Study of Organic Materials (Strengthening Agents for Grisailles and Stained Glass, Adhesives) used in Restoration
The “CONSTGLASS” European project, N°044339 (2007-2010), provided an opportunity to evaluate the main materials used for stained glass preservation-restoration, and asses their long-term effect, reversibility and re-treatability. The initial work undertaken in this regard on glass consolidation was continued in the “NANOMATCH” project, N°283182 (2011-2014), which covers an array of materials.
Preventive Stained Glass Protection Methods using External Glazing: Assessing Environmental Impact
The “VIDRIO” European project, N°EVK4-CT-2001-45 (2002-2005), provided an opportunity to assess the effectiveness of protective external glazing for stained glass windows, including evaluations of the systems deployed in the Sainte-Chapelle in Paris, the Basilica of Saint-Urbain in Troyes and Cologne Cathedral. The recommendations stemming from this study remain valid today.
- Claudine Loisel | Ingénieur de recherche