RETOUCHING MURAL PAINTINGS IN HYPOGEUM: PRELIMINARY STUDY AND FIRST RESULTS

This study was carried out during the ICR conservation project involving two of the mural paintings of the Saint Peter and Paul’s hypogeum in Matera. Retouching mural paintings preserved in such a peculiar environment as hypogea is not an ordinary operation. In these contexts, relative humidity approximating to 100% makes hygroscopic materials less durable, favouring biological growth on them. In addition, severe climatic conditions can lead to a fast degradation of retouching materials. Watercolours, extensively employed for retouching mural paintings, are not completely recommendable in such humid environments, so a research was planned to find a compatible and alternative binding media. A study was carried out on laboratory samples to select the most suitable binding media among the following: two synthetic resins, Laropal A81 and Regalrez 1094, and two natural products, Funori and arabic gum. Each binder was blended with two different pigments.  For each binder four different dilutions were tested, in order to find out how these factors could have affected the analysed properties. These products have been investigated in relation to their optical properties, wettability, vapour and water permeability, resistance to salt crystallisation and bioreceptivity. Some tests were repeated after an artificial ageing process, based on cyclical alternation of humid-cold and dry-hot exposure conditions. In addition to the laboratory tests, some in situ applications were performed. Amongst four binders, Regalrez 1094 showed the best results. Nevertheless, its bioreceptivity and applicability issues make necessary to continue and develop further research.