Chemical analysis of binding media in historic works of art

To get deeper insights into the painting or manufacturing technique of valuable historic works of art, to verify recipes found in contemporary sources, to clarify the degradation state of such objects, and to define the conservation or preservation treatment best suited to keep them for future generations, scientific investigations of works of art are regularly performed today. As from ancient times in producing such works of art a wide variety of natural binding media, including proteins, gums, resins, drying oils, and waxes, has been used as paint medium, for coatings, as adhesive or filling material, and for a number of other purposes, the characterisation of these media is of special interest. However, their clear identification is very difficult in general, because of their complex chemical composition, the natural variation of contents, their alteration due to ageing and environmental influences, and the application of not only single media but mixtures of different components. In addition the sampling of valuable artworks is restricted more and more and therefore very often only tiny little samples are available for analysis. Highly sophisticated analytical techniques, like e.g. Gas Chromatography Mass Spectrometry (GC/MS) and Fourier Transform Infrared (FTIR) Microscopy are needed to enable the investigation of these complex materials. For this research project three different analytical techniques are used to study certain issues related to the extensive and unique art collections of the Kunsthistorisches Museum (KHM), Vienna. At the same time a network for the investigation of natural binding media in valuable historic works of art is established between the Conservation Science Department of the KHM, the Institute of Humanities, Science and Technologies in Art, Academy of Fine Arts Vienna, and the Institute for Analytical Chemistry, Vienna University of Technology. The topics studied include the painting technique of very famous painters, like e.g. Titian and van Dyck, the investigation of treatments applied to old master paintings within the paintings conservation department of the KHM during the last 100 years, the painting technique of a class of very rare ancient objects - the Fayum mummy portraits -, and the characterisation of ancient adhesive and filling materials, which are normally composed of a mixture of different components. By performing these studies the comprehensive scientific and art historical care of the collections - both essential tasks of the KHM - and the development of preservation strategies best suited for the valuable and unique works of art, and comparable to international standards, will be supported.

Within the project a network for the organic analysis of works of art has been established between the Kunsthistorisches Museum (KHM), Vienna, the Vienna University of Technology and the Academy of Fine Arts Vienna. Consequently by now for the first time in Austria the opportunity exists to investigate valuable and unique artworks - of the KHM and other similar institutions - with respect to the organic binding media on a broader and more regular basis. This analytical studies also enable a targeted support of the selection of the best-suited restoration or conservation treatment in connection to the preservation of Austria`s cultural heritage. After the optimisation of the appropriate analytical procedures a number of selected objects was investigated concerning their original or later applied polychromy (paint layers), coatings, or adhesives in connection with questions of their production and the materials used as well as conservation problems. For example an original polychromy, a so-called "bronzing", could be documented underneath a gilding applied later on for three baroque tables by Giovanni Giuliani held in the Collections of the Prince of Liechtenstein today. Furthermore, the binding media in the paint tubes from the original paintbox of Arnold Schönberg were analysed. In connection to the comprehensive study of the paintings by Arnold Schönberg - kept in the Arnold Schönberg Center, Vienna, today - linseed oil with additions of beeswax, mastic, and essential oils (added to adjust the drying qualities of the paint and its final appearance) was identified as the main binding medium in the paints. The investigation of varnishes (uppermost transparent coatings) on paintings from the Picture Gallery of the KHM showed the continuous application of mastic in oil of turpentine as a restoration varnish in the KHM for the 19th and 20th centuries. In addition, on some paintings residues of earlier oil-based varnishes were detected. Due to the observation of certain components the application of the so-called "Pettenkofer method" - a widespread restoration treatment at the change from the 19th to the 20th century - was proven for the first time for the KHM. For the antique mummy portraits of the Collection of Greek and Roman Antiquities of the KHM the ancient adhesive was identified to be pine pitch. Earlier investigations using less developed analysis techniques were not able to show any useful results. Further studies included the analysis of the composition of coatings, e.g. lacquers from historical musical instruments held in the Collection of Ancient Musical Instruments of the KHM, of binding media from wall paintings, e.g. some frescoes from ceilings of the Palais Liechtenstein, or the polychromy of a variety of art objects. Eventually environmental related subjects, e.g. the composition of hazy films developing on the interior and exterior of glazings on paintings as well as on the surfaces of bronze sculptures were studied.