Early in the project, GCI staff met with a group of leading Czech conservators to help develop a consensus on intervention. Within the Czech conservation community, some believed that the mosaic should be removed, new housing found, and the original replaced by a copy; others maintained that the mosaic should be treated in situ. After a series of discussions, the Czech group came to a consensus agreement on treatment in situ. After considering the causes of deterioration and evaluating several in situ treatment options, the Czech-GCI team decided that a protective coating for the mosaic glass surface was the appropriate approach, if such a coating could be developed.

Scientific research in coating technology and development of a suitable protective coating system was, therefore, a major focus of the project. A variety of coating strategies were tried during past restoration attempts but a successful solution was not found. In collaboration with the Department of Material Science and Engineering at UCLA, the GCI conducted a multiyear investigation of a coating technology for the mosaic, testing protective coating methods and materials. A large number of high-performance coatings and protective coating systems were investigated with a series of tests conducted in situ and in the laboratory. This research identified sol-gel materials—a hybrid of organic and inorganic materials that have properties similar to glass but do not require very high temperatures for production or application—as the best coating materials currently available for the mosaic. These materials were then tested in custom-designed aging chambers at UCLA, the GCI, and in situ on test fields on the mosaic in Prague.

Several chemical and mechanical methods for the removal of corrosion layer were tested and evaluated with the conservators. Laboratory and in situ tests and examination of cleaned tesserae under optical and electron microscopes indicated that cleaning could best be accomplished with a stream of compressed air and microscopic glass particles. Using glass particles harder then the corrosion layer but softer than the mosaic tesserae would thoroughly remove the corrosion layer without affecting the glass surface.

The condition of the mosaics and the conservation treatment were graphically recorded following the methodology developed at the GCI. This methodology allowed the integration in digital environment of graphic data collected on paper. Having data in digital form permits quantitative evaluation of the extension of decay, helps in the interpretation and the analysis of the surface under study, and provides flexibility in presentation, exchange, and archiving of the data, as well as reproducibility.

Work Completed

  • Scientific study and understanding of the decay mechanism of the mosaic's glass.
  • Study of mosaic technology used for The Last Judgment.
  • Tests of methods to remove corrosion.
  • Research on coating materials, including in situ and accelerated aging tests.
  • Study of gilding technology.
  • Recording of the mosaic's condition.

Last updated: December 2009