Fluorination technique to identify the type of resin in aged vanishes and lacquers using infrared spectroscopy

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.