Homogeneity, Composition and Deterioration of Window Glass Fragments and Paint Layers from Two Seventeenth-Century Stained Glass Windows Created by Jan de Caumont (15801659)

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Publication Type:

Journal Article

Authors:

Schalm, Olivier; Caen, Joost; Janssens, Koen;

Source:

Studies in Conservation, Volume 55, Number 3, p.216-226 (2010)

Abstract:

During the conservation of two stained glass windows by Jan de Caumont at the Abbey 't Park (Heverlee, Leuven, Belgium) small fragments were removed from eight panes for analysis. Electron microscopy with energy dispersive X-ray sprectroscopy (SEM-EDX) was used to study the microstructure of several materials in these windows, and to perform quantitative analysis of the homogeneous materials. According to the SEM-EDX analyses, the glass appeared to be homogeneous. The deteriorated regions found in the fragments contained cracks, have a fractal appearance with stratifications of 2 μm in width and contained small islands of original unleached glass. Unfortunately, SEM-EDX did not allow a reliable chemical analysis of the different stratified layers due to the limitation in lateral resolution. The vitreous paint layer on one of the fragments consisted of lead glass surrounding many SiO2 and Fe2O3 particles. The green-blue and blue enamel paint layers were made with a low-melting SiO2-K2O-PbO glass. The colouring substance for the green-blue enamel paint layer was brass (i.e. an alloy of Cu and Zn), while for the blue enamel paint layer a substance known as saffre (a roasted sulphide ore rich in cobalt) was used. The compositions of the window glass fragments were all similar and consisted of high lime–low alkali (HLLA) glass (SiO2-K2O-CaO).