The historical varnish technology is of interest to various fields in cultural heritage. To understand the material properties of these historic surface coatings it is important to get insight in the technological background, i.e. the... more
The historical varnish technology is of interest to various fields in cultural heritage. To understand the material properties of these historic surface coatings it is important to get insight in the technological background, i.e. the relationship between the material and the processing method. This study has specifically focused on the use of pumice stone and bone ash often mentioned in historical sources as driers for oil-based coating systems. For this purpose lute and Italian violins from the period between the 16 th to the mid 18 th century were examined. Both, the main organic composition of the varnish and the addition of mineral additives were considered. Based on the analytical data and the corresponding information from historical written sources, the siccativation of oil-based varnishes with pumice stone and bone ash was simulated experimentally. The results of these reconstructions confirm that the technological know-how behind these varnishes is far more complex than it may appear at first glance and that the organic and inorganic components must be regarded as a balanced technological system where each of the various components has a specific function. In this context, these inorganic additives effectively induced accelerated drying, improved the mechanical film properties of young films and showed a stabilizing effect on the long-term degradation during aging.
Infrared spectroscopy (FTIR) is a standard technique for the characterisation of organic materials in conservation science. This analytical technique is particularly interesting to analyse historical varnishes from cultural artefacts, as... more
Infrared spectroscopy (FTIR) is a standard technique for the characterisation of organic materials in conservation science. This analytical technique is particularly interesting to analyse historical varnishes from cultural artefacts, as only minute samples are required. Some limitations apply, however, when analysing such chemically complex multi-component materials with interfering absorption bands. A previously introduced sample pre-treatment method using gaseous sulfur tetrafluoride SF4 has shown to widen the application fields of the IR-technique by improving its specificity. One of these new fields is its successful application to the characterisation of complex aged natural varnish and lacquer systems. The fluorination treatment leads to characteristic band shifts of four individual saturated and unsaturated acid groups attached at varying positions of the terpene backbone. This allows the separation of otherwise overlapping carbonyl bands of different ketones and ester groups. Based on this technique, inert and unique functional groups can be used as material specific markers to identify drying oil, shellac and different terpene resins in varnishes and lacquers. The proposed markers proved to be stable for several hundred years. These findings are particularly interesting, as it is now possible to trace such markers even in very old varnishes dating back to the 16th century – with a likewise simple technique.
The inclusion of minerals in Italian varnishes from the 16th to mid-18th centuries has long been a source of speculation. Analysis of micro-samples from multiple locations on 30 reference instruments from the 16th to the mid-18th century... more
The inclusion of minerals in Italian varnishes from the 16th to mid-18th centuries has long been a source of speculation. Analysis of micro-samples from multiple locations on 30 reference instruments from the 16th to the mid-18th century as well as a comprehensive study of written sources have revealed a centuries-old tradition of using pumice stone and calcined bones as additives for oil varnishes. These new findings represent a paradigm shift in our understanding of historical varnishes and open up exciting new perspectives.
The historical varnish technology is of interest to various fields in cultural heritage. To understand the material properties of these historic surface coatings it is important to get insight in the technological background, i.e. the... more
The historical varnish technology is of interest to various fields in cultural heritage. To understand the material properties of these historic surface coatings it is important to get insight in the technological background, i.e. the relationship between the material and the processing method. This study has specifically focused on the use of pumice stone and bone ash often mentioned in historical sources as driers for oil-based coating systems. For this purpose lute and Italian violins from the period between the 16 th to the mid 18 th century were examined. Both, the main organic composition of the varnish and the addition of mineral additives were considered. Based on the analytical data and the corresponding information from historical written sources, the siccativation of oil-based varnishes with pumice stone and bone ash was simulated experimentally. The results of these reconstructions confirm that the technological know-how behind these varnishes is far more complex than it may appear at first glance and that the organic and inorganic components must be regarded as a balanced technological system where each of the various components has a specific function. In this context, these inorganic additives effectively induced accelerated drying, improved the mechanical film properties of young films and showed a stabilizing effect on the long-term degradation during aging.
