Zwischengoldglas: Technology of production, material analyses and conservation

Abstract

Zwischengoldglas (gold between glass) objects represent a special category of glass with the decoration placed between two or more layers of glass. The main production centre was located in Bohemia, where most of these objects were made during the eighteenth century. Zwischengoldgläser were extraordinary objects, extremely difficult to produce. Their production demanded high glass-blowing, cutting, grinding, gilding and engraving skills. Each production step meant a risk and many pieces were damaged while assembling glass parts with hot resin. Recently a comprehensive survey of the Zwischengoldglas collection of the Museum of Decorative Arts in Prague was conducted. Four hundred objects were photographed and condition assessment was performed. Organic materials were analysed using micro-Fourier transform infrared spectroscopy (micro-FTIR), which showed that the objects were assembled using a natural pine resin, colophony. The red resin, typically found on the base and on the medallions, is colophony stained with madder. Prussian blue and copper resinate colourants were also identified. In specific cases, restoration of Zwischengoldgläser was considered and in a very few cases was carried out. The treatment of four objects is described, representing typical damage and illustrating decisions and practice for restoration.

Keywords:

• Zwischengoldglas
• Colophony

Acknowledgements

We would like to thank the Corning Museum of Glass where the research, supported by the Fulbright Foundation, was conducted. We also thank H. Köenigsmarková, Director of the Museum of Decorative Arts in Prague and P. Špaček, Head of the Conservation Department, for their consistent support in this long-term project. We would also like to thank R. Zrcková for FTIR carried out at the Customs Technical Laboratory of the Czech Republic.