Airborne fungi and bacteria pose a severe challenge for conservators, as they can settle on artistic surfaces, leading to chemical, physical and aesthetic degradation of artworks. A new air-cleaning system has been developed to reduce indoor airborne microorganisms by leveraging the antimicrobial potential of Tea Tree (Melaleuca alternifolia) Essential Oil (TTEO) encapsulated within the pores of MCM-41 mesoporous silica microparticles (MCM-TTEO), thereby extending its antimicrobial activity and enhancing its efficacy. Experimental data showed a progressive release of TTEO from the MCM-TTEO system during the 5 weeks monitoring. The release rate was quite linear in the first week, reaching about 16.2%, before plateauing at approximately 30% in the next weeks. A comparison of the performances of the MCM-TTEO system with those of the non-encapsulated (‘free’) TTEO was performed using a comprehensive air quality monitoring approach, which tracked temperature, relative humidity, microbial loads and particulate matter. Results demonstrate that the MCM-TTEO system maintained higher biocidal activity over the 5-week study period than the free EO. Furthermore, the biocidal efficacy increased when the MCM-TTEO system was used in direct contact with microorganisms. These promising findings highlight the potential for exploring different combinations of the two components in both passive and active configurations, including the development of air filtration systems.

Microbial colonization of heritage materials is a well-known conservation issue. When necessary, it is removed using mechanical, physical, or chemical methods, with biocide formulations being a common choice. The need to reduce dependence on conventional biocides has led to the exploration of innovative alternative methods and new formulations with biocidal properties for the conservation of heritage objects. Alternative approaches include natural compounds such as plants’ essential oils. While these natural options show promise, they present challenges—such as inconsistent effectiveness, possible toxicity, and the need for thorough compatibility testing with historic materials. Therefore, although some concerns are legitimate, the “run” to alternative substances is a growing concern as well. A comprehensive selection and examination of international research articles from the past two decades on this subject has been conducted. The detailed and critical analysis of existing data on essential oils, hydrolates, and other plant-derived extracts studied to prevent and/or eradicate the colonization of microbial communities on heritage objects focused on the effect on microorganisms in controlled environments, in situ applications on microorganisms, encapsulation in hydrogels and emulsions, toxicity and ecological impact, and alterations of heritage materials. The review also discusses the advantages, limitations, and practical implications of these strategies.

This paper describes and discusses the results of scientific experiences of the physical and mechanical methods used to control and inhibit the growth of lichens and biofilms that grow on indoor and outdoor historical stone artworks. It provides an extensive selection and examination of international papers published in the last two decades on the issue. The great advantage of physical and mechanical methods lies in the lack of potential risks associated with the irreversible application of microbicides. Indeed, they do not introduce any harmful chemicals to humans, to the environment, or to heritage objects. This review focuses on the application of (i) electromagnetic radiation, (ii) high temperatures, (iii) lasers, and (iv) mechanical tools, and includes the main achievements, limitations, and potential applications of the examined studies.

Historical stone artworks are susceptible to damage in many environments. Biodeterioration caused by lichens and biofilm-forming microorganisms on these artworks has gained growing attention in the field of cultural heritage conservation. The current approach is focused on planned removal of lithobionts whenever they cause objective damage and/or structural impairments to the substrate. Cleaning may sometimes be followed by the application of organic and/or inorganic products for protection and con- solidation of the artworks. The lithobiontic recolonization after cleaning and coating treatments is con- sidered as one of the most challenging subjects nowadays. It is expected to occur in outdoor conditions, particularly on porous substrates, in shaded areas, and in areas that remain moist over time. Two as- pects connected to this topic are the recolonization of surfaces after removal of biofilms and lichens, and the recolonization of cleaned surfaces treated with consolidants and/or water repellents. This paper re- views the scientific advances of the last two decades on i) recolonization of artworks, and ii) interaction between synthetic polymers and lithobionts.(c) 2023 Consiglio Nazionale delle Ricerche (CNR). Published by Elsevier Masson SAS. All rights reserved.

Although ceramic objects are an important part of the worldwide cultural heritage, few investigations on the effects of lithobiontic growth on their outdoor conservation are available in the literature. Many aspects of the interaction between lithobionts and stones are still unknown or strongly debated, as in the case of equilibria between biodeterioration and bioprotection. This paper describes research on the colonization by lithobionts on outdoor ceramic Roman dolia and contemporary sculptures of the International Museum of Ceramics, Faenza (Italy). Accordingly, the study i) characterized the mineralogical composition and petrographic structure of the artworks, ii) performed porosimetric measurements, iii) identified lichen and microbial diversity, iv) elucidated the interaction of the lithobionts with the substrates. Moreover, v) the measurements of variability in stone surface hardness and in water absorption of colonized and uncolonized areas were collected to assess damaging and/or protective effects by the lithobionts. The investigation showed how the biological colonization depends on physical properties of the substrates as well on climatic conditions of environments in which the ceramic artworks are located. The results indicated that lichens Protoparmeliopsis muralis and Lecanora campestris may have a bioprotective effect on ceramics with high total porosity and pores with very small diameters, as they poorly penetrate the substrate, do not negatively affect surface hardness and are able to reduce the amount of absorbed water limiting the water ingress. By contrast, Verrucaria nigrescens, here widely found in association with rock-dwelling fungi, deeply penetrate terracotta causing substrate disaggregation, with negative consequences on surface hardness and water absorption. Accordingly, a careful evaluation of the negative and positive effects of lichens must be carried out before deciding their removal. Regarding biofilms, their barrier efficacy is related to their thickness and composition. Even if thin, they can impact negatively on substrates enhancing the water absorption in comparison to uncolonized parts.

In the past several years, products and methods alternative to conventional biocides, used in the conservation of cultural heritage objects, have been investigated increasingly to eradicate or prevent the growth of microorganisms and lichens on stone artworks. Although some concerns about conventional biocides are legitimate, the "run" to alternative substances is growing concern as well. This review aims at contributing to the interpretation of recent findings in innovative methods and substances focusing on i) resistance of biofilms to environmental stressors, including antimicrobials; ii) metals and metal-based compounds including nanoparticles; iii) mixtures of metal nanoparticles and metal oxides with water repellents and consolidants; iv) natural compounds (essential oils of plants, secondary metabolites of lichens, microbial by-products, microorganisms, extracts from marine organisms); v) toxicity of essential oils; vi) alternative chemicals (Ionic liquids, dimethyl sulfoxide gel, hydrolase enzymes). This review also includes a discussion on the advantages, drawbacks and limitations of the examined studies to encourage a constructive discussion among professionals involved in the field of stone heritage conservation, and to develop a sustainable path for managing the biological colonization. This state-of-the-art review indicates that further research is needed to propose alternative compounds to conventional biocides.

This study integrates the complex research conducted on the sources of brown discolorations that occur on marble statues (fifteenth century) of the Church of Orsanmichele in Florence (Italy). They underwent conservative interventions in the past and the brownish discolorations on their surfaces strongly altered the clear tone of the marble. In this study, Carrara marble model specimens were treated with organic and inorganic substances (non-pasteurised milk; linseed oil; walnut oil; ammonium oxalate; microcrystalline wax; beeswax; milk + linseed oil; and milk + ammonium oxalate + linseed oil) to simulate their effects on the stone. Some of the substances were commonly used in the past (as on the Orsanmichele statues) but most of them are still used in many countries. The treated specimens were exposed to natural and artificial ageing. The main results of the research were (i) the specimens treated with linseed oil, milk + linseed oil, and milk + linseed oil + ammonium oxalate showed a severe change of colour after either artificial or natural ageing; (ii) an extensive polymerisation of the organic substances occurred; (iii) calcium oxalate and several oxidised diacylglycerols (DAGs) and triacylglycerols (TAGs) were the last chemical products of the oxidation processes induced by ageing; (iv) Maillard reaction, producing brownish coloration, likely occurred in specimens containing milk as a result of the interaction between sugars and proteins.

AbstractCultural heritage objects composed of inorganic materials, such as metals and stones, support microbial life. Many factors affect the growth of microorganisms: moisture, pH, light, temperature, nutrients. Their colonization relates closely to the nature of the substrata as well as to the characteristic of the surrounding environment. This chapter contains an overview of the complex relationships among microbial growth, materials, and the environment. It emphasizes issues on bioreceptivity of stones and the factors influencing biological colonization, focusing on the biological alteration of inorganic heritage objects and on the agents of biodeterioration. It outlines the effect of biofilms and lichens in terms of degradation of substrata and includes a discussion on an important topic, the bioprotection of stones by biofilms and lichens. In summary, this chapter aims to discuss these issues and review the recent literature on (i) biofilms and lichens colonizing inorganic materials, (ii) the limiting factors of this colonization, (iii) the deteriorative aspects, and (iv) the protective effects of the colonization.

Weathering processes seriously affect the durability of outdoor marble monuments. In urban environments, a very common deterioration phenomenon is the dark discoloration or blackening of marble. This paper describes a multidisciplinary study on the state of conservation of white marbles of the Florence Cathedral and the microbial community involved in their deterioration. The study is focused on the widespread dark discoloration of marble analyzed in two differently exposed sites of the Cathedral. It aims to provide information useful for future interventions to control the microbial growth. By chemical and petrographic analysis, in situ and ex situ microscopy, and cultivation and identification of microorganisms, it was found that (i) the darkening is mainly due to the growth of black fungi and dark cyanobacteria and (ii) the state of conservation of marble and the growth pattern of microorganisms seems to be linked to the microclimatic conditions, in particular to solar radiation exposure. This is the first report on the lithobiontic community inhabiting the Florence Cathedral marbles, with a more detailed investigation of the culturable mycobiota.

The control of biodeterioration encompasses the operations undertaken to eliminate the biological growth and, possibly, to delay a new colonization. The current attitude is generally oriented toward its planned removal whenever it causes an objective damage and/or structural impairments to the substratum. The English Cemetery, located in the centre of Florence, offers interesting features for a research focused on the removal of biofilms and lichens growing on stone surfaces of some tombs. The study compared the efficacy of two methods based on physical approach (mechanical cleaning with a brush and microwave heating) with a chemical approach using biocide ROCIMA™ 103 to remove biofilms and lichens from each tombstone. The research, focusing on methodologies with low impact for the environment, tested the efficacy of an innovative portable system that produces localized microwave heating. Its great advantage lays on lack of the potential risks associated with the irreversible application of microbicides. The assessment of the treatments' efficacy was carried out monitoring the chlorophyll a fluorescence's parameters, informative on the vitality and stress responses of photosynthetic organisms. The long-term monitoring of the recolonization after the treatments was performed for five years. The mechanical cleaning eliminated the superficial layer of biofilms and lichens but not the cells within the stones. The biocide was efficient in killing the biological growth; almost no recolonization was observed after about five years. The innovative microwave treatment was effective on biofilms and lichens, eliminating also cells present in the bulk of the substrata, but recolonization was observed after 15 months. This suggests that, dopo treatment aggiungere virgola the microwave treatment should be performed more frequently than biocide treatments yet guaranteeing lower impact on the environment.

The Ferrara cathedral and Parma baptistery are exceptional medieval monuments and results of a technical study of the polychrome sculptures and reliefs are presented here. The results are an extension of past diagnostic projects carried out between the 1970s and 90s, and support the re-examination of previous investigations. Scientific and historical accounts describe medieval sculpted portals of European cathedrals as a prime example of the diffusion of the polychrome painting techniques. The technical study of paint fragments of ancient polichromy is complex and requires sophisticated instrumentation to inform colour reconstructions. In this study, micro-Raman classified pigments and gas chromatography mass spectrometry (GC/MS) identified the organic binding media on the pre-treated stone, primers, painted layers, and gilding. GC/MS analysis of samples from the Ferrara cathedral detected fatty acids that most closely match linseed oil and dehydroabeitic acid, a marker for pine resin, which was detected for the first time in the primer from the Ferrara cathedral panels. The Parma baptistery samples contained amino acids indicating the presence of protein and oil. Raman analysis added novel results on the pigments used, such as lead-tin yellow type I and orpiment, as well as on the state of conservation of paint layers. The data were also compared to a wide range of publications and were found to significantly contribute to the knowledge and research in architectural polychromy in the Romanesque-Gothic era.

The research complements a study (Pinna et al., 2012) carried out to evaluate the effectiveness of mixtures of consolidants and water-repellent products (tetraethylorthosilicate, methylethoxy polysiloxane, Paraloid B72), with biocides (tributyltin oxide, dibutyltin dilaurate, copper nanoparticles) applied in situ to prevent biological growth on stones. The mixtures were tested over time on trial areas of three substrates - marble, sandstone, and plaster – in the archaeological site of Fiesole (Firenze, Italy). The 8-year-long study showed that the recolonization of the three substrates after the conservation treatment related mainly to their bioreceptivity and to the climatic conditions. Although the mixtures of water repellents and consolidants with biocides and copper nanoparticles were effective in reducing the recolonization, they did not play a crucial role in preventing biofilms and lichens growth. This study demonstrated that it was not possible to draw common conclusions regarding the products’ performance on the examined stones. Copper nanoparticles proved to be a suitable alternative to traditional biocides because they did not alter stones colour and contributed to the prevention of recolonization. The study provided information on the succession of fungi and lichens on untreated and treated stones, as well as on the variations of water repellency of treated stones.

The research complements the complex study carried out to understand the source of brown discolourations of ten marble statues in the Church of Orsanmichele in Florence, Italy. Originally located in exterior niches, the statues were restored to reverse the extensive alterations they had undergone throughout the centuries. One of the major alterations was the application of a dark brown patina that dated just after 1789. After the statues were placed indoors, brownish discolourations started to appear on their surfaces. Cross sections were examined using FTIR mapping and immunological methods. In parallel, the pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) data already obtained from the statues' scrapings were compared with data from aged casein films applied to microscope glass slides and aged milk-treated marble. All the statues had been treated with milk-based substances before the time the bronze patina was applied. The values of temperature and illumination of the room were important factors in the ageing of organic substances and in the formation of calcium oxalates. It is likely that products of thermo-oxidation and photo-oxidation of the oils together with the oxalates caused the darkening. The marble samples corresponded to a Lunense provenance.

Introduction The paper describes the complex investigations carried out to understand the sources of the brown chromatic changes that have occurred on ten marble statues dated back to the first half of the 15th century and now located in the Church of Orsanmichele in Florence, Italy. When the statues were removed from the outdoor niches for restoration in the 1980s, they appeared covered with a dark brown patina (called ‘bronzatura’) that dated to interventions occurred just after 1789. Archival documents confirmed that they had been carried out to make the marble statues look like bronzes. Because of the removal of the dark patina carried out by the Opificio delle Pietre Dure in the 1990s, the marble almost regained its distinguishing clear tonality even if darker areas remained. After the statues were placed indoors at the end of restoration, brownish discolorations started to appear on their surfaces. Results Research began by using various non-invasive analyses (photographs under ultraviolet illumination, fluorescence lifetime imaging, x-ray fluorescence). The results of UV fluorescence tests and FLIM showed that the fluorescence emission’s distribution map does not have distinctive and homogeneous characteristics in relation to the areas with the discoloration. Therefore, it is not a superficial film, but rather a phenomenon affecting the marble structure. Then we performed invasive analyses on samples from some statues. The results of optical microscopy, ATR-FTIR and Raman spectroscopy on cross sections, pyrolysis-gas chromatography/mass spectrometry on powdered samples from the surfaces and/or the bulk of the marble allowed the identification of the various substances involved in the chromatic alteration. Most important was the detection of weddellite and gypsum on the surface and within the marble. This finding, combined with the presence of lipids inside the stone, suggests that mineralization of treatments have occurred, causing discolorations. Conclusions Even though the study focuses on the statues from Orsanmichele, their issue nevertheless should not be considered specific to them. Marble discolorations are a widespread phenomenon whose complete understanding needs a complex series of analyses and only the combination of non-invasive and invasive analyses can fulfill this goal.

Fluorescence LIDAR imaging has been already proposed in several studies as a valuable technique for the remote diagnostics and documentation of the monumental surfaces, with main applications referring to the detection and classification of biodeteriogens, the characterization of lithotypes, the detection and characterization protective coatings and also of some types of pigments. However, the conservation and documentation of the cultural heritage is an application field where a highly multi-disciplinary, integrated approach is typically required. In this respect, the fluorescence LIDAR technique can be particularly useful to provide an overall assessment of the whole investigated surface, which can be profitably used to identify those specific areas in which further analytical measurements or sampling for laboratory analysis are needed. This paper presents some representative examples of the research carried out in the frame of the PRIMARTE project, with particular reference to the LIDAR data and their significance in conjunction with the other applied techniques. One of the major objectives of the project, actually, was the development of an integrated methodology for the combined use of data by using diverse techniques: from fluorescence LIDAR remote sensing to UV fluorescence and IR imaging, from IR thermography, georadar, 3D electric tomography to microwave reflectometry, from analytical techniques (FORS, FT-IR, GC-MS) to high resolution photo-documentation and historical archive studies. This method was applied to a 'pilot site', a chapel dating back to the fourteenth century, situated at 'Le Campora' site in the vicinity of Florence. All data have been integrated in a multi-medial tool for archiving, management, exploitation and dissemination purposes.

Salt crystallization is a major damage factor in stone weathering, and the application of inappropriate protective products may amplify its effects. This research focuses on the evaluation of two protective products' performance (organic polydimethylsiloxane and inorganic ammonium oxalate (NH4)2(COO)2·H2O) in the case of a salt load from behind. Experimental laboratory simulations based on salt crystallization cycles and natural weathering in an urban area were carried out. The effects were monitored over time, applying different methods: weight loss evaluation, colorimetric and water absorption by capillarity measurements, stereomicroscope observations, FTIR and SEM-EDS analyses. The results showed minor impact exerted on the short term on stones, particularly those treated with the water repellent, by atmospheric agents compared to salt crystallization. Lithotypes with low salt load (Gioia marble) underwent minor changes than the heavily salt-laden limestones (Lecce and Ançã stones), which were dramatically damaged when treated with polysiloxane. The results suggest that the ammonium oxalate treatment should be preferred to polysiloxane in the presence of soluble salts, even after desalination procedures which might not completely remove them. In addition, the neo-formed calcium oxalate seemed to effectively protect the stone, improving its resistance against salt crystallization without occluding the pores and limiting the superficial erosion caused by atmospheric agents.

OPINION article Front. Microbiol., 02 April 2014Sec. Microbiotechnology Volume 5 - 2014 | https://doi.org/10.3389/fmicb.2014.00133

In this study, some mixtures of consolidants or water-repellent products and biocides developed to prevent biological growth, were tested over time on three stone substrates with different bioreceptivity. The performance of both traditional (tetraethylorthosilicate, methylethoxy polysiloxane, Paraloid B72, tributyltin oxide, dibutyltin dilaurate) and innovative compounds (copper nanoparticles) was assessed using colour measurements, the water absorption by contact sponge method, and observation under stereo and optical microscopes. The application of the mixtures had also the purpose of controlling re-colonization on stone after a conservation treatment. The study site was the archaeological Area of Fiesole; the mixtures were applied in situ to sandstone, marble and plaster which had been cleaned beforehand. An innovative aspect of the study is that, by using non-invasive methods, it also permitted monitoring the mixtures' effectiveness in preventing biological growth. The monitoring results made it possible to assess the bioreceptivity of the treated stones (sandstone, marble, plaster) over a period of almost three years. The results showed that the mixtures of consolidants or water-repellent products with biocides were effective in preventing biological growth on both a substrate with low bioreceptivity like plaster and a substrate with high bioreceptivity such as marble. The innovative mixture of nano-Cu particles with a water-repellent yielded good results in terms of preventing biological colonization. Moreover, they apparently did not affect the substrates' colour. Mixtures of nano-Cu particles with a consolidant and a water-repellent hold great promise for preventing re-colonization of stone after conservation treatment.