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In this work, we investigated the potential of PVA-borax hydrogel for cleaning limestones and the dependence of the cleaning on the porosity of the rock and on the action time of the hydrogel treatment. Towards this goal, we used a nuclear magnetic resonance (NMR) spectrometer, developed for non-invasive and non-destructive applications on cultural heritage. T2-NMR parameters were quantified on different samples of Lecce stone and Travertine cut perpendicular (Pe) and parallel (Pa) to the bedding planes under different experimental conditions: untreated samples, treated with Paraloid B72 and cleaned with PVA-PEO-borax hydrogel applied for 4 min and 2 h. The T2 results suggest that the effectiveness of the cleaning strongly depended on the porosity of the stones. In Lecce stone, the hydrogel seemed to eliminate both the paramagnetic impurities (in equal measure with 4 min and 2 h treatment) and Paraloid B72. In Travertine Pe, characterized by a smaller pore size compared to Lecce stone, no significant effects were found regarding both the cleaning and the treatment with Paraloid B72. In Travertine Pa, characterized by a larger pore size than the other two samples, the hydrogel seemed to clean the paramagnetic agents (it worked better if applied for a longer time) but it did not appear to have any effect on Paraloid B72 removal.

The society has become increasingly interested in using natural products over chemicals for cleaning activities. In this study, the cleaning potential of formulations embedded in a hydrogel matrix and composed respectively of essential oils (EOs) of Origanum vulgare, Thymus vulgaris, and Calamintha nepeta, and their respective main active components (EO-ACs), viz., Carvacrol, Thymol, and Pulegone, on a phototropic biofilm growing on granite was investigated. In addition, and for comparative purposes, analysis with the combination of the three EOs, the combination of the three EO-ACs, and Preventol RI-80&reg, (one of the most effective commercial cleaning agents based on quaternary ammonium salts) in all three cases embedded in a hydrogel matrix, as well as only the hydrogel matrix, distilled water, and Preventol RI-80&reg, in both latter cases applied with brush, were also studied. The cleaning effect of the treatments was assessed immediately after the treatment and after one and two weeks by color spectrophotometry, a reliable tool to evaluate the presence and vitality of the phototrophs and the cleaning effectiveness in granite. C. nepeta and its active component Pulegone proved to be the most effective and yielded similar results, comparable to those of uncolonized granite, and better than those obtained with Preventol RI-80&reg, applied with brush (most common way), especially at the end of the experiment. These promising first results support the suitable use of the phytochemical compounds used on phototrophs field where there are still few published studies and encourage further investigation toward the evaluation of their exhibited biocidal activity.

Travertine is a sedimentary carbonate rock widely used in Roman arts and frequently subjected to biodeterioration. In this preliminary multi-analytical study, three essential oils (EOs) from T. vulgaris, O. vulgare, C. nepeta and their respective phenolic major components (thymol, carvacrol, pulegone) were selected to evaluate their biocidal potential against a multi-species biofilm grown on a travertine test wall located inside Sapienza University Campus in Rome. A preliminary characterization of the biofilm occurred through the employment of genomic methodologies. It has been confirmed the presence of microorganisms belonging to fungi, plant and bacteria kingdoms amplifying the rDNA in the characteristic regions (ITS, 18S, 16S) by performing PCR amplification with specific primers. For this purpose, two different biofilm sampling procedures, one completely non-invasive (swab in physiologic saline solution) and one micro-invasive (adhesive tape) have been employed: the adhesive tape performed better than swab in relation to DNA purity and quantity. After the biofilm characterization, the application of the phytochemicals occurred. For the realization of formulations, the EOs and their major components have been incorporated inside an innovative hydrogel matrix conceived for the cleaning of cultural heritage. The biocidal and cleaning action was evaluated with colorimetric measurements before and after the application of the products and, in the case of the surfaces treated with the essential oils, these measurements have been repeated 6 weeks after the end of the treatment. It emerged that the formulations containing the active phenolic compounds have, in most cases, a better efficacy against the multispecies biofilm. Anyway, it was verified that the biocidal action of the essential oils lasts in time, since colour variation towards the original colour of the surface have been determined 6 weeks after the end of the procedure.