Cristina M. Belfiore

Application of spectrometric analysis to the identification of pollution sources causing cultural heritage damage

Black crusts are recognized to have been, up to now, one of the major deterioration forms affecting the built heritage in urban areas. Their formation is demonstrated to occur mainly on carbonate building materials, whose interaction with an SO2-loaded atmosphere leads to the transformation of calcium carbonate (calcite) into calcium sulfate dihydrate (gypsum) which, together with embedded carbonaceous particles, consequently forms the black crusts on the stone surface. An analytical study was carried out on black crust samples collected from limestone monumental buildings and churches belonging to the European built Heritage, i.e., the Corner Palace in Venice (Italy), the Cathedral of St. Rombouts in Mechelen (Belgium), and the Church of St. Eustache in Paris (France). For a complete characterization of the black crusts, an approach integrating different and complementary techniques was used, including laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), Fourier transform infrared spectroscopy, optical and scanning electron microscopy. In particular, the application of LA-ICP-MS permitted to obtain a complete geochemical characterization in terms of trace elements of the black crusts from the inner parts to the external layers contributing to the identification of the major combustion sources responsible for the deterioration over time of the monuments under study. In addition, the obtained results revealed a relation between the height of sampling and the concentration of heavy metals and proved that the crust composition can be a marker to evaluate the variation of the fuels used over time.

An analysis of the black crusts from the Seville Cathedral: A challenge to deepen the understanding of the relationships among microstructure, microchemical features and pollution sources

The Cathedral of Seville is one of the most important buildings in the whole of southern Spain. It suffers, like most of the historical buildings located in urban environments, from several degradation phenomena related to the high pollution level. Undoubtedly, the formation of black crusts plays a crucial role in the decay of the stone materials belonging to the church. Their formation occurs mainly on carbonate building materials, whose interaction with a sulfur oxide-enriched atmosphere leads to the transformation of calcium carbonate (calcite) into calcium sulfate dihydrate (gypsum) which, together with embedded carbonaceous particles, forms the black crusts on the stone surface. To better understand the composition and the formation dynamics of this degradation product and to identify the pollutant sources and evaluate their impact on the stone material, an analytical study was carried out on the black crust samples collected from different areas of the building. For a complete characterization of the black crusts, several techniques were used, including laser ablation inductively coupled plasma mass spectrometry, Fourier transform infrared spectroscopy, micro infrared spectroscopy, optical and scanning electron microscopy. This battery of tests provided information about the nature and distribution of the mineralogical phases and the elements within the crusts and the crust-substrate interface, contributing to the identification of the major pollution sources responsible for the deterioration of the monument over time. In addition, the results revealed a relation among the height of sampling, the surface exposure and the concentration of heavy metals. Finally, information has been provided about the origin of the concentration gradients of some metals.

A new methodological approach for the chemical characterization of black crusts on building stones: a case study from the Catania city centre (Sicily, Italy)

Mineralogical, petrographic and chemical analyses were carried out on black crusts covering the stone surface of monuments and buildings of the historical city centre of Catania, one of the most beautiful Baroque places in eastern Sicily. Black crusts were studied through the careful and synergic employment of traditional techniques, including polarizing optical microscopy (POM), scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDS), and infrared spectroscopic techniques (FT-IR), in combination with an innovative technique, i.e.laser ablation inductively coupled mass spectrometry (LA-ICP-MS). The validity of such an integrated approach to study black crusts has been recently demonstrated by the authors. The main goal of this study was to develop and test the reliability of the LA-ICP-MS method on black crusts in order to evaluate the degree of chemical contamination of examined stones and to determine the role of the different sources of pollution in Catania, both anthropogenic (domestic heating, industrial combustion, vehicular traffic) and natural (emissions by Mt Etna) in the formation of crusts. Results obtained demonstrated that this innovative approach has a double potential in the study of black crusts, since it allows the analysis of alteration and degradation processes induced by migration of specific chemical elements from the crust to substrate, and, at the same time, it represents a reliable indicator of the environmental pollution.

Application of laser ablation ICP-MS and traditional techniques to the study of black crusts on building stones: a new methodological approach

IntroductionIn this work, we propose an innovative application of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) as a methodological approach for the chemical characterisation of black crusts on stone monuments, associated with traditional micro-morphological (optical and scanning electron microscopy) and infrared spectroscopic techniques (FTIR).MethodsThis new approach was tested on black crusts developing on two marble substrates, one, the columns of the San Cosimato cloister in Rome, and the other, a sculpture representing an angel, located in Pessano con Bornago, a small industrial town near Milan.DiscussionThe main aim of this study was to develop and test the reliability of the LA-ICP-MS analytical method on black crusts and to explore the idea that trace element concentrations in black crusts can be applied to investigate their origin and the relations between concentrations of polluting elements in black crusts and environmental conditions.ConclusionThe results obtained by applying traditional techniques find considerable support in the innovative method used here, which could determine the concentrations of a large number of trace elements (including heavy metals) in the black crusts examined, and thus could also be used as a reliable indicator of environmental pollution.

New insights on the consolidation of salt weathered limestone: the case study of Modica stone

The deterioration of a stone material is related to its pore structure, which affects the interaction between surface and environmental agents. Indeed, salt crystallization is one of the most dangerous weathering agents in porous building materials. The crystallization pressure of salt crystals, growing in confined pores, is found to be the main cause for damage. The consolidation of such degraded stone materials represents a crucial issue in the field of restoration of cultural heritage. This paper presents the results of a laboratory experimentation carried out on Modica stone, a limestone largely used in the Baroque architecture of eastern Sicily. Several specimens, collected from a historical quarry near the city of Modica, were artificially degraded by salt crystallization tests. Then, degraded samples were treated with three different consolidating products: a suspension of nanolime in alcohol, a suspension of nanosilica in water, and ethyl silicate dispersed in white spirit. A systematic approach, including mercury intrusion porosimetry, peeling tests and point load test, was used to evaluate the correlation between the salt crystallization and the micro-structural features of the limestone, as well as the efficacy of treatments. The consolidating behavior of the tested products was also appraised by repeating salt crystallization tests after consolidation, in order to assess the resistance of treated stone to further salt crystallization phenomena. Results showed that nanolime provides a good resistance to the stone; conversely, ethyl silicate, although inducing an enhancement of stone cohesion, leads to an increase of the crystallization pressure, which generates dangerous susceptibility to weathering.

Cappadocian ignimbrite cave churches: stone degradation and conservation strategies

The focus of this research is to investigate the minero-petrographic features and the conservation aspects of the stone materials from some rock-hewn churches in Cappadocia region (Turkey) in order to choose the most appropriate consolidating systems to improve the resistance against the weathering and degradation phenomena of this unique world heritage site. In this study, specimens from the Tokali church in the Goreme’s Open Air Museum, and from the Forty Martyrs Church in Şahinefendi were analysed by optical microscopy and X-ray diffraction in order to examine the properties of the rock and especially how well preserved it is. The ignimbrite samples show a porphyritic structure with vitrophyric groundmass and crystalloclastic-vitrophyric texture. The presence of smectite and illite caused serious damage to the rock structure such as cracks, decohesion, exfoliation, and disaggregation phenomena.The consolidation tests were performed on the ignimbrite specimens, sized according to the standard procedure, by using three commercial silica-based products: NanoEstel, Estel 1000, and Estel 1100. The consolidant penetration was investigated by titanium labelling procedure followed by scanning electron microscopy–energy dispersive spectroscopy analysis. Colour measurements were used to study the possible chromatic changes due to the treatments. The capillary test was performed to evaluate the amount of water absorbed by the stone surfaces before and after the consolidating treatments. Lastly, the surface cohesion due to the consolidation was investigated by using the peeling test carried out on untreated and treated samples.The consolidating tests showed that the solvent-based products (Estel 1000, Estel 1100) exhibit a better distribution than the aqueous suspensions (NanoEstel). Nevertheless NanoEstel gives better results in the capillary absorption test, suggesting that this product has the ability to leave the stone porous structure substantially unaltered.

The Baroque architecture of Scicli (south-eastern Sicily): characterization of degradation materials and testing of protective products

Scicli and the other baroque cities of the “Val di Noto” (Catania, Militello, Caltagirone, Palazzolo, Siracusa, Noto, Ragusa e Modica), were recently included in the World Heritage List. These cities were completely destroyed following the earthquake of 1693 and then were involved in an intense period of rebuilding and artistic flowering. In particular, Scicli was reconstructed with the almost exclusive use of a local calcarenite, which belongs to the Ragusa Formation. Due to its nature, this carbonate rock is subject to many alteration and degradation forms (chromatic alteration, alveolization, differential disaggregation, efflorescence, decohesion, exfoliation and detachment). Therefore, different products (beeswax, vegetable oils, natural and synthetic resins) were used in the past often with the aim to preserve the monuments from decay. In this study, through a diagnostic analysis, the degradation materials occurring in the churches of St. Matteo, St. Michele and Carmine in the city of Scicli, as well as residues of treatments carried out in the past, have been identified. In addition, three different types of protective products were tested in laboratory, with the aim of assessing their protective effectiveness in terms of hydrorepellence and response to accelerated aging and salt crystallization tests. Laboratory tests showed that, among the tested products, the Polisiloxane can be regarded as the most suitable for this type of substrate.

The behaviour of consolidated Neapolitan yellow Tuff against salt weathering

Salt crystallization is a strong weathering agent in porous building materials. The crystallization pressure exerted by salt crystals, growing in confined pores, is found to be one of the main causes for damage. This paper presents the results of laboratory experimentation carried out on the Neapolitan Tuff, a pyroclastic rock largely used in Campanian architecture. Several specimens, collected from a historical quarry near the city of Naples, were treated with two different consolidating products: a suspension of nanosilica in water (Syton X30®) and ethyl silicate (Estel 1000®) dispersed in organic solvent (TEOS). Untreated and treated samples were then artificially degraded using salt crystallization tests in order to assess the effectiveness of consolidation treatments. A systematic approach, including mercury intrusion porosimetry, peeling tests and point load test, was employed to evaluate the correlation between the salt crystallization and the micro-structural features of the tuff. In addition, in order to make a correlation between porous structure of materials and susceptivity to salt crystallization, the calculation of the crystallization pressures was performed. In all samples, at the early stage of crystallization, the presence of gypsum was revealed, coming from the precipitation of sulphate ions, introduced during the test, and sodium ions, coming from the zeolites within the stone. Results showed that both consolidants increase the resistance of tuff to salt crystallization, although they induce an increase in crystallization pressure. Ethyl silicate, however, shows a better behaviour in terms of superficial cohesion, even after several degradation cycles.

The Oceanus statue of the Fontana di Trevi (Rome): The analysis of black crust as a tool to investigate the urban air pollution and its impact on the stone degradation

This paper deals with the analysis of black crust coming from the statue of Oceanus belonging to the Fontana di Trevi (Rome). This monument is undoubtedly one of the main touristic attractions of Rome. During the restoration held between 2014 and 2015, some diagnostic analyses had been carried out. It has been highlighted that the sheltered surfaces suffer the formation of black crust, especially on the marble statues. The possibility to sample those degradation products, together with the unaltered substrate, represented an excellent opportunity to characterize the marble itself, to assess the impact of the urban air pollution on the stone material, and to detect the pollutant on a precise timescale. In fact, it is known that the previous restoration of the fountain had been carried out between 1989 and 1991 then, information about the air pollution over the last 25years can be highlighted, because it has been proved that black crusts act as passive samplers of pollution. In order to fully characterize those samples, several techniques were used, including optical and scanning electron microscopy, X-ray diffraction, laser ablation inductively coupled plasma mass spectrometry, infrared spectroscopy and ion chromatography. Furthermore, a new methodology based on CHN (Carbon, Hydrogen, Nitrogen) analysis has been developed for the quantification of the two main constituents of the carbonaceous fraction present in the black crusts, i.e. OC (organic carbon) and EC (elemental carbon). This integrated approach proposed in the present study allowed us to gain information about the mineralogical phases and the elements within the crusts and at the crust-substrate interface, giving the possibility to identify the pollution sources causing the stone decay within the monument.

Comparison between TOF-ND and XRD quantitative phase analysis of ancient potteries

A non-invasive time-of-flight neutron diffraction (TOF-ND) analysis has been performed on archaeological pottery fragments from the excavation sites in the “Strait of Messina” area (Sicily, Southern Italy). The revealed quantitative information on the mineralogical composition have been compared, in the case of two samples representative of coarse and fine grained pottery, with the weight fractions of the crystalline phases as obtained from X-ray diffraction on powders (XRPD), for different amounts of extracted powder. From the results, the consistency of these micro-destructive and non-invasive approaches has been checked. This research may contribute to better define the most efficient sampling and analytical method for the determination of mineralogical composition on ceramics different in structure and composition.