Michela Ricca

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.

Mosaic marble tesserae from the underwater archaeological site of Baia (Naples, Italy): determination of the provenance

This paper is focused on defining the geographic provenance of eight marble tesserae of archaeological interest used for the opus sectile floor slabs of the Villa con ingresso a protiro , located in the Roman underwater Archaeological Park of Baia (Naples, Italy). Geochemical, isotopic and petrographic data show that Carrara, Thasian and Docimium/Afyon marbles were used in manufacturing the mosaic constituting the floor slabs of the Roman Villa.

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.

Provenance study of building and statuary marbles from the Roman archaeological site of Villa dei Quintili (Rome, Italy)

The present work represents the first study addressed to the provenance attribution of marbles from the Villa dei Quintili, an important Roman archaeological site located in the south-eastern area of Rome (Italy). The monumental villa was built in the 2nd century A.D. at the behest of the brothers Sesto Quintilio Condiano and Sesto Quintilio Valerio Massimo. Later (182 A.D.), the Emperor Commodus confiscated the villa, transforming it into an imperial residence until the 3rd century A.D. Different analytical techniques, including polarized optical microscopy, scanning electron microscopy coupled with energy dispersive spectrometry (SEM-EDS), carbon and oxygen stable isotope ratio determinations, inductively coupled plasma mass spectrometry and X-ray diffraction, were used to identify the provenance sources of seventeen white marble samples belonging to statues, covering slabs and architectural elements of the villa. For such a purpose, data obtained were compared with existing databases relative to white marbles commonly used in antiquity collected from historic quarries in the Mediterranean area.Results show that several precious marbles from different Mediterranean sites were used for the statuary as well as for decorative and architectural elements of the Villa thus remarking the importance of the archaeological site.

Biodeterioration of marble in an underwater environment

This study examines the deterioration of geomaterials used throughout history that today may be found lying on the ocean floor. Submerged archaeological sites including cargoes from shipwrecks or ancient city ruins have been a topic of interest from a perspective of in situ musealization, as a way of making underwater cultural heritage accessible to the public. In an experimental study conducted at an underwater archaeological site in the Bay of Cádiz (SW Spain), we subjected two types of marble (Carrara and Macael) to three conditions to which submerged archaeological objects are often exposed: full exposure to the water column, natural processes of burial and unearthing, or permanent burial. After an 18-month study period, the factor found to mostly affect these materials was their biological colonization. This factor was assessed by estimating total surface biocover and the rate of surface biocolonization, and also through the identification of skeletons and associated alteration forms by light microscopy, and scanning electron microscopy (SEM). Biofouling and bioerosion were the main causes of biodeterioration and dependent on the position of the marble specimens in the seawater. The response of both materials was similar, though dolomite crystals in the Carrara marble acted as a protective barrier against actively penetrating microorganisms. These investigations have allowed the study of tracers left by epilithic encrusting organisms and endolithic bioeroders on marbles intentionally exposed to seawater, providing new insights to the understanding of the biodeterioration processes occurring in cultural heritage stones, with significant implications when they are part of underwater archaeological remains.

The colors of the Fontana di Trevi: an analytical approach

ABSTRACT During the last restoration of the Fontana di Trevi -Rome (2014–2015), it has been performed a diagnostic investigation to characterize the materials used to build and obtain the colors of the surfaces of some architectural elements of this fountain. According to the restoration teamwork needs, we focussed our efforts on the dome over the central statue of Oceanus, on the bas-relieves on the sides of the dome, and on the cliff where the water flows. Several samples were collected from these elements and therefore, they were subjected to an analytical approach including infrared spectroscopy, optical and scanning electron microscopy. The achieved results indicated the use of red earth pigments on the dome. The same pigment has been revealed on the bas-relieves, although their colors have an additional contribution due to degraded layers. Samples taken from the cliff showed a complex stratigraphy, although a white scialbo has been identified as original layer, testifying the intentions of the authors in term of color rendering. This information was essential for the restores in order to choose the proper intervention procedure for each investigated surface. The research testified the importance of an integrated diagnostic analysis to preserve the original colours of monuments and building.

Diagnostic analysis of bricks from the underwater archaeological site of Baia (Naples, Italy): preliminary results

In this multidisciplinary contribution, several diagnostic tests were carried out in order to characterize the archaeological materials, as well as the alteration and degradation products, present in the submerged archaeological site of Baia (Naples, South Italy). Founded by the Romans in the 1st century B.C., this archaeological area represents one of the greatest evidence of Roman architecture and it includes ancient ruins whose structures range from maritime villas and imperial buildings. Fragments of bricks belonging from walls of a monumental villa, called Villa con ingresso a protiro, were studied with different and complementary techniques. In particular, polarized optical microscopy and X-ray diffraction were performed in order to characterize the raw materials employed for their production, while to evaluate the state of conservation and identify the biodeteriogen agents, samples were studied under a stereomicroscope and scanning electron microscopy. Analytical data highlighted that: a) different types of bricks were used in the ancient roman city of Baia; b) the presence of several degree of biological colonisation is mainly correlated to the type of temper used for their production.

An archaeometric approach of historical mortars taken from Foligno City (Umbria, Italy): news insight of Roman Empire in Italy

This research has been focused on the study of mortars from four bridges of the ancient city of Foligno (Umbria, Italy), located along the old path of the Topino-Tinia River. An archaeometric study was undertaken to analyse ten archaeological samples in order to define textural features, chemical composition and raw materials used for their production. For this purpose, different analytical methods were used, such as polarising optical microscope (POM), X-ray diffraction (XRD) and electron microprobe analysis coupled with energy-dispersive spectrometry (EMPA-EDS).