In recent years, attention has been paid to finding eco-friendly products that could represent an alternative for the chemicals usually used during conservation procedures. In the field of the devitalization of biological patinas, the most studied products are essential oils (EOs). Several works tested EOs in vitro on microorganisms isolated from stone artifacts but few applied these products on real artworks colonized by a complex patina. In the present work, the biocidal effect of two EOs (cinnamon bark and oregano) and two EO-based products (Biotersus and Essenzio) was compared to that of three chemical biocides commonly used in the conservation of stone artifacts (Biotin R1+R2, NewDes50, and Preventol RI50). The products were applied by brush in situ on a marble slab characterized by a green patina. The biocidal activity was evaluated by analyzing the chlorophyll fluorescence and quantifying ATP through biochemical tests. Furthermore, the products’ interference with stone was evaluated by colorimetric measures on sedimentary rock samples. The results indicate that chemical biocides exhibited biocidal activity of greater than 99.5% with a single application, while cinnamon oil (at a 1% concentration) and Essenzio required two applications to achieve the same level of efficacy. Conversely, oregano oil and Biotersus were not able to effectively reduce microorganism vitality, even with repeated applications.

Consolidation of mural paintings in hypogea is challenging because of their severe microclimatic conditions, characterized by high humidity levels, low air circulation, the presence of salts efflorescence, and the detrimental growth of biodeteriogen agents. Traditional consolidant products show significant drawbacks when used in hypogeum. Organic compounds, such as acrylic emulsions, are bio-receptive and some inorganic consolidants, such as silica-based products, show a lack of compatibility with the original substrate, which could lead to a reduction in permeability and an increase in the mechanical resistance of the external layer. The presence of solvents in their formulations, particularly short-chain alcohols that can activate germination of fungal spores, leads to the release of great amounts of volatile organic compounds, which are particularly harmful in the hypogeic environment. To solve these problems, restorers of the Istituto Centrale per il Restauro (ICR) decided to use a new aqueous nanolime dispersion, NANOLAQ, consisting of pure and crystalline Ca(OH)₂ nanoparticles dispersed in water, produced by an innovative and sustainable patented procedure. After laboratory testing, the product has been applied on site, on a medieval mural painting in the Ss. Peter and Paul hypogeum in the UNESCO site of Matera (Italy), monitoring the performance in terms of cohesion of the paint layer and preservation of aesthetic features.

Several lime mortars for the repair of painted plasters of the rock-cut church of Ss. Pietro and Paolo in Matera were studied. They were designed taking into account both aesthetic criteria that need to be fulfilled in the field of paintings restoration, and physical–mechanical compatibility with the original materials on site, i.e., the pre-existing plasters and the supporting rock. Mixes with calcareous and silica aggregates, based on different grain size proportions, were prepared to fill missing portions of the original painted plaster. The effects of the mineralogical nature and size of the aggregates on the characteristics and properties of the mixes were investigated in relation to the microstructure, physical–mechanical features and resistance to salt ageing. At the end of the experimental campaign, the overall performance was evaluated.

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.

Several lime mortars for the repair of painted plasters of the rock cut church of Ss. Pietro and Paolo in Matera were studied. They were designed taking into account both aesthetic criteria that need to be fulfilled in the field of paintings restoration, and physical-mechanical compatibility with the original materials on site, i.e. the pre-existing plasters and the supporting rock. Mixes with calcareous and silica aggregates, based on different grain size proportions, were prepared for filling missing portions of the original painted plaster. The effects of the mineralogical nature and size of the aggregates on the characteristics and properties of the mixes were investigated in relation to the microstructure, physical-mechanical features and resistance to salt ageing. At the end of the experimental campaign, the overall performances were evaluated.