Advanced analytical investigation on degradation markers in wall paintings

Understanding the original techniques in the creation of an artwork is a prerequisite for the selection of the most appropriate conservation method. This is particularly essential in wall paintings where control of potential agents of deterioration and efficient monitoring are limited due to the scale of the paintings and their exposure to uncontrollable environmental fluctuations. Analytical studies are increasingly focused on the investigation and study of degradation products of organic binders originally added in the paintings on a lime-based plaster ground. In the framework of IPERION-CH (Integrated Platform for the European Research Infrastructure ON Cultural Heritage) project, a collaborative task is dedicated to obtain knowledge about original organic materials used in wall paintings by evaluating and comparing different innovative methodologies and conventional diagnostic techniques used for the investigation of markers related to alteration mechanisms and degradation products. The non-invasive and microsampling methodology is first optimized on well-defined models that have been designed to simulate different painting techniques with limewater and five organic binders in different relative proportions. Future investigations will focus on the application of the optimized methodology on archaeological samples. In the present paper, preliminary results on a selected set of models, submitted in different stages of a well-established artificial ageing protocol, demonstrate the specific complementary input of each analytical technique included in the analytical approach (colour measurements, micro FTIR-ATR analyses in cross-sections, Evolved Gas Analysis-Mass Spectrometry and Gas Chromatography-Mass Spectrometry). The comparative evaluation and interpretation of the results is a step forward in the optimization of the approach and in relating the analytical findings detected on the analysed samples to the original compounds and the possible changes for each group of binders (proteins/gums) due to degradation or interaction depending on the pigment/metal ion present.