Study of organic coatings on metal based museum objects

Within a still-ongoing research project (FWF, project no. P15640-N03) a gas chromatography-mass spectrometry (GC-MS) system was installed at the Conservation Science Department of the Kunsthistorisches Museum (KHM) for the investigation of complex natural binding media systems in historic works of art. Together with a post- doctoral scientific position, funded by the same project, these installations allowed to build-up a database of natural polymers for GC-MS and Pyrolysis-GC-MS investigations as well as the verification and improvement of the experimental methods to be applied for the analysis of unique and valuable works of art. Within the proposed project these improved sample preparation and analyses methods for (Py)-GC-MS, the connected databases and a set of about 9000 unaltered and artificially aged reference samples will be available for the investigation of organic coatings on metal based museum and indoor objects. This investigations will be complemented by Fourier Transform Infrared attenuated total reflection (FTIR-ATR) microscopy investigations, performed at the Department for Conservation, University of Applied Arts Vienna. A set of 650 Renaissance and Baroque bronze sculptures, held in the Collection of Sculpture and Decorative Arts of the KHM will be studied with respect to their organic coatings. These coatings contain original "patinas" by tinted organic lacquers - applied by the artists themselves - as well as conservation lacquers - applied later to prevent the objects from corrosion or to influence their aesthetic appearance. A systematic study of the coatings and, therefore, state of the objects` surfaces has never been done before and is needed for art historical research as well as for the development of conservation concepts to preserve these unique and valuable objects in the best possible way. In addition, the organic coatings present on the sarcophagi-ensemble within the Imperial Crypt in the church of the Capuchin Friars (the Kapuzinergruft), Vienna, will be studied. The tin-lead alloy sarcophagi were originally covered with organic coatings based on shellac and dyes after 1790. Due to the high relative humidity within the Imperial Crypt the sarcophagi developed severe corrosion and were, therefore, treated by several restoration campaigns from 1964 up to 2002 applying epoxy resin based, nitrocellulose, and/or acrylic based lacquers, respectively. A survey performed by the Conservation Department of the University of Applied Arts in 2002-2003 revealed severe corrosion mainly where the recent restoration coatings had been applied. To allow for a well- advised conservation and preservation of the sarcophagi the investigation of the chemical changes within the multi- layered coating systems as well as their influence on the metal surfaces is necessary to be performed at first.