Methodology of analytical study for provenance determination of calcitic,calcite–dolomitic and impure marbles from historical quarries in the Czech Republic

The present provenance study was focused on marbles from historical quarries of one geological unit (Bohemian Massif, Czech Republic) exhibiting complex polyphase geological evolution. A combination of mineralogical–petrographic, geochemical and physical methods has been tested i.e. optical microscopy (OM) of the whole rock, X-ray diffraction (XRD) of the insoluble residues, petrographic image analysis (PIA) of carbonate grains, cathodoluminescence (CL) of microfacies, stable isotope ratio analysis (SIRA) of carbonates in the groundmass and secondary veins, Raman microspectrometry (RM) of the carbonaceous matter and bulk magnetic susceptibility (MS) of the whole rock.Based on the results of historical quarries and the artefacts from Pernštejn Castle and Prague Castle, the most effective way for provenance determination of marbles seems to be a combination of petrographic methods (including quantitative approaches), cathodoluminescence, and stable isotope study. Less conventional methods (e.g. Raman microspectrometry or physical properties like bulk magnetic susceptibility) are very useful for provenance studies on impure calcitic and dolomitic marbles that include carbonaceous matter, magnetic minerals or silicates. For the first time, Raman data on reduced carbonaceous matter permitted differentiation amongst marbles of different origin.     

A procedure for determining the chemical composition of binder and aggregate in ancient mortars: its application to mortars from some medieval buildings in Pisa

The use of a scanning electron microscope equipped with a microanalytical system is proposed for characterising ancient mortars. A calculation procedure is presented that allows a determination of the binder and aggregate compositions (including volatile components) from microprobe data collected on the binder, and chemical, mineralogical, petrographical and physical data collected on the mortar bulk sample. The proposed procedure is applied to 11 mortar samples from three historical monuments built in Pisa throughout the Middle Ages. The binder of the analysed samples consists of a carbonate crystalline fraction and an amorphous carbonate-free fraction that makes up from 20 to 60 % by weight of the binder. The aggregate composition, on average, is close to that of the Arno River sands.     

Effect of low and high fluence on experimentally laser-cleaned sandstone and marlstone tablets in dry and wet conditions

The eligibility of laser cleaning is tested on regionally specific sculptural stones. Marlstone and sandstone represent the most common building, architectural and sculptural stones employed in the Czech Republic since the Romanesque period. These stone types differ greatly from the marbles on which positive results have been obtained using laser cleaning. Experimental samples were prepared by sawing rock cores. Artificial blackening of samples’ surfaces simulates natural black patinas. The experimental laser cleaning was conducted using Nd:YAG commercial laser (Laserblast 50) at two different fluences—the low one corresponds to the minimum operating capability of the equipment, and the high fluence represents the maximum operating mode of the equipment (i.e. in the ordinary operating range of the equipment). The samples were cleaned under dry and wet conditions. Use of a high fluence resulted in cratering/spalling that is discussed in terms of rock mineralogical composition (presence of clay minerals), adsorption of moisture on clay minerals and physical properties (porosity). Tensional fracturing (evidenced by scanning electron microscopy) along the cleaned surface is the main mechanism of sample destruction due to the vaporization of adsorbed moisture and due to the different elasticity of present rock-forming minerals. Observed discoloration due to high fluence and insufficient cleaning effect of low fluence present other problems encountered.     

Durability of the artificial calcium oxalate protective on two Florentine monuments

The use of the artificial calcium oxalate treatment providing a protective patina to marble sculptures and a mural façade has been investigated. The longevity of the protective method is controlled at a distance of 3–4 years from its application on two diversely externally exposed Florentine monuments. Micro samples were analysed by optical microscopy (OM), scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX) and MicroRaman spectroscopy to characterize products of deterioration and the efficacy of the applied treatment.Decay is predominately noted at a superficial level and in all cases the calcium oxalate is still present, thus the protective action of the treatment is confirmed and moreover, a consolidant effect is also considered. Both statues present fractures and cavities filled with calcium oxalate residues and various degradation products such as gypsum, lichens and pollution particles. This study contributes to ascertain that artificial calcium oxalate prevents further decay of carbonate materials in urban polluted environments.     

Degradability of building stone: Influence of the porous network on the rate of dissolution of carbonate and evaporitic rocks

The susceptibility to weathering of eleven carbonate and evaporitic Spanish building rocks was studied by means of dissolution experiments. Mineralogy, petrology, geochemistry and porosity of the rocks were also characterized in order to determine the potential relationships between these properties of the rocks and their dissolution rates. Rock slabs were submerged in a 0.1 M HCl acid solution for 72 h and the amounts of Ca, Mg and S released were measured, as well as the weight loss of the samples during the acid attack. Alabasters, which presented very low porosity, were dissolved to a lesser extent than limestones and dolostones in the time of the experiment. A significant positive correlation was found for connected with the weight loss of the rocks during dissolution and with the kinetic rate of Ca dissolution. Overall, the results highlight the influence of the porous network in the degradability of building stones by controlling their rate of dissolution. There is a positive correlation for all the rocks between weight loss along acidic attack and connected porosity, but no relationship between mineralogical and petrographical composition and susceptibility to dissolution.     

A color image segmentation method as used in the study of ancient monument decay

In the cultural heritage area, it is of fundamental importance to characterize and classify the conservation state of the materials constituting ancient monuments, in order to study and monitor their decay. Generally, the decay diagnosis is provided by “naked eye” analysis done by expert scientists “walking around” the artifact and recording the conservation state of each individual element they observe. In this paper, a color image segmentation approach, based on histogram threshold and edge detection techniques is presented, to extract degradation regions, characterized by holes or cavities, from color images of stone-materials. The goal is to provide an aid to the decay diagnosis by segmenting degraded regions from color images, computing quantitative data, such as the area and perimeter of the extracted zones, and processing qualitative information, such as various levels of depth detected into the same zones. Since color is a powerful tool in the distinction between objects, a segmentation technique based on color, instead of intensity only, has been used to provide a clearer discrimination between regions. The study case concerns the impressive remains of the Roman Theatre in the city of Aosta (Italy). In particular, we have processed and analyzed some color images of the theatre puddingstones, acquired by a camera.     

A Bacillus subtilis cell fraction (BCF) inducing calcium carbonate precipitation: Biotechnological perspectives for monumental stone reinforcement

Monumental stone decay is a consequence of the weathering action of physical, chemical and biological factors, which induce a progressive increase in porosity. To cope this degradation, bacterial calcium carbonate mineralization has been proposed as a tool for the conservation of monumental calcareous stones. The advantage of this kind of treatment is to obtain a mineral product similar to the stone substrate, mimicking the natural process responsible for stone formation. In this work, the possibility to induce CaCO₃ mineralization by a bacteria-mediated system in absence of viable cells was investigated and tested on stone. Our results showed that Bacillus subtilis dead cells as wells as its bacterial cell wall fraction (BCF) can act as calcite crystallization nuclei in solution. BCF consolidating capability was further tested in laboratory on slab stones, and in situ on the Angera Church, a valuable 6th century monumental site. New crystals formation was observed inside pores and significant decrease in water absorption (up to 16.7%) in BCF treated samples. A little cohesion increase was observed in the treated area of the Angera Church, showing the potential of this application, even though further improvements are needed.     

X-ray radiography and tomography for monitoring the penetration depth of consolidants in Opuka – the building stone of Prague monuments

Stone consolidation is one of the major restoration treatments used for historical monuments preservation. A natural stone is a complicated heterogeneous porous system making the process of consolidation dependent on many variables. In practical restoration aims, for a given stone type, the selection of a suitable consolidant and consolidation conditions therefore remains a complex issue. The impregnation depth is a key factor for the assessment of the treatment efficiency. The combination of state-of-the-art hybrid pixel semiconductor detectors with newly available micro-focus X-ray sources makes possible to apply X-ray radiography, an ideal non-destructive tool, for penetration depth monitoring. In this study, high-resolution X-ray radiography is used for monitoring the penetration depth of organosilicon consolidants in the Opuka stone. The penetration depth has been evaluated in relation to the time of consolidation, stone porosity and consolidation mixtures properties. The exact influence of the X-ray contrast agent on the consolidation depth has been investigated as well. The information obtained provides supplementary knowledge on the suitability of investigated products for the treatment of this type of stone. In our study, the capabilities of X-ray radiography have been demonstrated on X-ray radiography simple projections, high-resolution computed tomography (CT) as well as on the dynamic processes monitoring. The results thus can serve also as an instrumental and methodological example applicable for consolidation monitoring of other stone types.     

Vaterite in the mortars of a mosaic in the Saint Peter basilica,Vatican (Rome)

The vaults of the Saint Peter basilica in Vatican (Rome) are decorated with mosaics whose realisation is dated to the end of the 16th century. The mortar layers beneath the mosaics are realised with the so-called “Roman stucco”, a kind of mastic specifically employed as a binder in the mosaic's supporting layers. Its empirical recipe was known and reported by 18th century authors, accounting for the use of lime, travertine powder added to a mixture of herbs and linseed oil. A recent restoration of the mosaics has allowed to characterise the mortars from a compositional point of view by individuating the inorganic mineralogical fraction and by chemically characterising the organic components. The study of stucco samples has been performed through polarising microscope observations, X-ray diffraction (XRD) analyses, thermal analyses (TA) (thermodifferential-DTA and termogravimetric-TGA analysis), Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy, pyrolysis-gascromatography (PY-GC)–mass spectrometry. The analyses have allowed to distinguish between original stucco, produced and utilized at the same time of the realisation of the mosaics, and other mortars, presumably employed in later times during restoration interventions. The outcomes of the mineralogical investigation and TA indicate the presence of four different types of stuccos, here considered as four characteristic groups. The mineralogical analyses indicate that all the samples are constituted of two main phases: calcite and vaterite and the TA, beyond the quantification of the calcium carbonate content, have shown the presence of organic components in the stucco. The organic fraction was characterised by PY-GC–mass spectrometry, confirming the presence of the linseed oil cited in the ancient recipes. The very interesting outcome of this study is the occurrence of the rare calcium carbonate polymorph vaterite. The ATR-FTIR spectroscopy on the stucco gives further contribution to a better understanding of the FTIR spectrum of the rare mineral and an explanation of its formation is tentatively given.     

Laser cleaning of stone artefacts: a substitute or alternative method?

Laser cleaning of ancient marble and stone monuments is nowadays a well-accepted procedure in conservation. Operators and specialists are presently divided between those giving maximum confidence to this method of cleaning and others who, in contrast, are strongly critical and emphasise possible drawbacks and damages caused by laser. As any other method of cleaning, laser also offers advantages but at the same time is limited by drawbacks. Most conveniently, it should be integrated with the other methods. On the basis of the above considerations, the authors are proposing a combined procedure using laser cleaning as a first step – in this way removing the relevant part of black gypsum encrustation – followed by chemical methods as a final step. The latter, conveniently, could be accomplished by means of anion exchange resins, better than ammonium carbonate. An experimental check-up was made of four different methods applied on three different lithotypes on the façade of the Florentine Cathedral. Laser, micro-sandblasting, ammonium carbonate and sodium EDTA were the cleaning methods compared, whilst Carrara marble, green Serpentine (Verde di Prato) and a red limestone were the three lithotypes. Results are commented by showing differences in the advantages and drawbacks among the different methods on the various lithotypes.     

Unusual differential erosion related to the presence of endolithic microorganisms (Martvili,Georgia)

The presence of a diffuse biodeterioration phenomena can be observed across large areas of the outer surface of the limestone walls of the Church of the Virgin in Martvili. A differential erosion phenomenon was detected, suggesting a possible association with biological colonization. The erosion phenomenon is characterized by a circular discoloration leading progressively to the detachment of flakes of limestone at its center. Since the aforementioned process has not been described in the literature until now, the present study was focused on the interpretation of its origin and evolution. Three sides of the Church are affected by a variety of occurrences of circular differential erosion which display different stages of the process, whereas the western side is affected by epilithic growths across its entire surface. Surveys of the petrographic, mineralogical and physical features of the stone were made, and parameters such as density and porosity were recorded. Samples were analyzed by optical microscopy and SEM analysis in order to detected the presence of microorganisms whose species were then identified by means of morphological and molecular examinations. The study of cross-sections stained using the PAS method has confirmed the causal connection between microorganisms and the deterioration phenomena, providing information about their spread of penetration into the substrate and their substantial potential for causing damage. Dryness appears to be the main ecological condition favoring endolithic rather than epilithic growth. The most common isolated microorganisms were cyanobacteria (Chroococcales) and, to a lesser extent, meristematic fungi. The characteristics of the stone, and especially some endogenous discontinuities related to the accumulation of sedimentary layers and to the action of stone carving tools, might explain why the same differential erosion phenomenon occurs in specific areas of the block stones. The development of the differential erosion phenomenon shows a variety of stages of biological colonization. The progressive evolution of the deterioration process has been observed in detail: (a) firstly, white circular discolorations appear on the stone, which darken over time eventually becoming almost black; (b) circular perforations appear around the perimeter; (c) and finally a flake detaches from the center, leaving a deep depression in the stone.     

The funerary klinai of tomb 1 from Amphipolis and a sarcophagus from ancient Tragilos, eastern Macedonia: a physico-chemical investigation on the painting materials

Optical and SEM-EDS microscopy, X-ray powder diffraction and micro FT-IR spectroscopy investigations of the funerary klinai (couches) of Tomb 1 from Amphipolis and a stone sarcophagus from ancient Tragilos—two painted monuments made by Macedonian craftsmen of the Early Hellenistic period—identified the original materials and painting technique, as well as synthetic materials used as consolidants during past restoration treatments. The original organic binders and the superficial modern coatings have been identified by micro FT-IR spectroscopy applied directly to the sampled powders or tiny fragments and to their solvent—soluble fractions. The pigments identified on the couch of Amphipolis are: red and yellow ochre, cinnabar, Madder lake, paratacamite and antlerite, carbon black, calcium carbonate, kaolin and gypsum. The identification of egg and animal glue confirms the application of tempera and secco techniques. The detection of polymers such as polydimethylsiloxane, polyvinyl acetate and alkyd resins, is related to modern restoration products. The pigments attested on the paintings of the Tragilos' sarcophagus are: red and yellow ochre, Egyptian blue, malachite, carbon black, calcium carbonate and gypsum. The absence of organic binders combined with the constant presence of calcium carbonate in all the examined samples suggests the use of lime as the binding medium in the painted decoration of the sarcophagus. The presence of Paraloid B72 is related to recent conservation treatments.     

Quantitative modeling of blistering zones by active thermography for deterioration evaluation of stone monuments

Infrared thermography for stone monuments to date has primarily focused on qualitative analysis to judge the location of defect zones using relative temperature differences, but there are difficulties in mapping a blistering zone and quantitatively calculating its area. Therefore, this study used quantitative modeling to map blistering zones with graduated heating thermography. To achieve this goal, the following steps were performed: acquisition of thermographic images by passive and active methods, construction of a temperature distribution curve, establishment of the critical temperature and transitional zone, classification of the relative deterioration grades of the blistering zone, monochrome processing, vectorization, and deterioration evaluation of the blistering zone. After evaluating the blistering degree of the specimen through modeling, the total areas and rates were calculated as 359.3 cm² and 80.1%, respectively. This study was very useful for identifying the location, area, and relative degree of deterioration of blistering zones that were not easily detectable with the naked eye. In the future, if quantitative modeling of blistering zones is actively applied to deterioration maps, the reliability of deterioration evaluation for stone monuments will be improved, and additional deterioration, such as scaling, may be prevented.     

Validating chemical and structural changes in painting materials by principal component analysis of spectroscopic data using internal mineral standards

This work shows the capability of principal component analysis (PCA) to detect molecular, chemical and mineralogical changes in historic painting materials subjected to a thermal ageing test (< 250 °C). To simulate the heat-induced alterations an ageing accelerated process was performed on two sets of samples containing two mineral phases (hydroxyapatite and quartz) and two organic compounds (collagen and albumin). The chosen minerals behaved as internal standards during the tests since they are stable and chemically inert at the tested temperatures. Raman microscopy (RM) was applied to characterise one set of samples made of bone, containing ca. 70% hydroxyapatite and 30% collagen. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy was used to study the other set of samples made of four different quartz/albumin mixtures with quartz contents of 30%, 50%, 70% and 90% (w/w). The aim was to identify the ideal proportion of internal standard to be validated by ATR-FTIR and PCA, determined to be 70%. PCA analyses detected changes in the molecular structures of the organic components while the internal mineral standard remained stable. Moreover, the internal standard IR/Raman bands were constant during the tests and confirmed that the results of PCA analyses were independent of instrumental and technical factors, as well as sample collecting and handling. This demonstrates the potential benefits of our approach to study historical painting materials, which have suffered any type of heat-induced alteration.     

Protective effect of endolithic fungal hyphae on oolitic limestone buildings

This study presents characterizations of weathering forms of the same oolitic limestone from four quarries and eight monuments exposed on various environmental conditions focusing on the waterproofing effect of endolithic organic matter. Patinas were analyzed by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDX), capillarity coefficient through weathered and unweathered sides, gypsum content and porous network morphology by epoxy resin molding. Study of weathering forms on old quarries indicates that lichens colonization (Verrucaria nigrescens and Caloplaca aurantia) can fill the superficial porous network with a dense network of lichenised fungal hyphae. Capillary coefficient measurement on natural and calcinated samples showed that endolithic organic matter can waterproof the stone and could act as a sulfate contamination barrier. Similar endolithic organic layer due to ancient lichens growth are found on some antique monuments of the Nîmes downtown and could explain their well-preserved state, unlike decayed 19th century churches that were never colonized by lichens.     

A multi analytical approach to discriminate the Italian colored marble “Portasanta” from Portasanta “Marmor Chium” (Greece)

The “marble” Portasanta from Caldana (Grosseto, Italy) takes its name from the strict resemblance to the ancient Marmor Chium (also this called Portasanta) coming from the island of Chios in Greece. In this work, a complete characterization of the Italian Portasanta was made: chemical (X-ray fluorescence and isotopic analyses), mineralogical (X-ray diffraction on the bulk sample and on insoluble residue after acid attack), physical (water accessible porosity and imbibition coefficients), petrographical (optical microscopy) and mechanical (compressive strength test) analyses have been carried out in order to obtain a better distinction between Italian and Greek “marble”, sometimes mistaken. The Portasanta from Caldana (Italy) was quarried surely in the sixteenth century, but a possible use of this material during Roman time is still in doubt. The study of samples from some Tuscan archaeological sites (Torraccia di Chiusi, Siena and Roselle, Grosseto) allows us to confirm the use of Portasanta from Chios for the Torraccia site and that of Caldana for Roselle.     

Consolidation of stone blocks prior to placement: A case study of the Roman wall in Tarragona (Spain): Report and methodology

The possible pre-consolidation of the stones used to repair the Roman wall of Tarragona was studied, on the premise that this had been carried out prior to placement in the wall. A detailed study of the stones was conducted in order to determine whether they had been treated, and if so, how this had been done. A semi-quantitative X-ray mineralogical analysis using the Rietveld method was performed, together with porosity and textural analyses. This paper concludes with a discussion of how the stones studied here were pre-consolidated using lime slurry.     

Decay regions segmentation from color images of ancient monuments using fast marching method

This work faces the problem of detecting decay zones from color images of stone materials. In Cultural Heritage, the extraction of degradation regions from images of ancient monuments represents an important step forward in studying and analyzing the state of preservation of historical buildings. Generally the decay diagnosis is provided by “naked eye” analysis done by expert scientists “walking around” the artifact and recording the conservation state of each individual element they observe. In addition to this kind of investigation, the application of an image segmentation strategy to color images of stony materials can be used in order to extract regions characterized by a visible chromatic alteration, changes in color, for example, as oxidation or concretion. This paper features a color image segmentation approach founded on the fast marching numerical method. We have applied this technique for its possibility to work locally, that is, only the contour of the region under study is processed. In addition to this method, we present a global approach, that is, the possibility to extract decay regions from the entire image; these regions are spatially disconnected but with similar colorimeter value. The main aim of the present work is to provide a tool that helps the expert to contour the degraded regions. In this sense even if the results of the proposed procedure depend on the expert evaluation, the approach can be a contribution to improve the efficiency of the boundary detection process. The study case concerns the impressive remains of the Roman Theatre in the city of Aosta (Italy). In the image segmentation process the color space L*a*b* is utilized.     

Environmental conditions controlling the chemical weathering of the Madara Horseman monument,NE Bulgaria

The conditions that led to the deterioration of the Madara Horseman sculpture, a relief carved in a sandy limestone cliff in north-east Bulgaria, were studied, with most emphasis on the chemical weathering at the stone–atmosphere interface. Total deposition sampled close to the monument contains high concentrations of NH₄⁺ and K⁺, which shows the influence of the dense vegetation in the area, and Ca²⁺, which reflects the cliffˈs weathering products. Ca²⁺ is also one of the most important constituents (next to aluminosilicates) of the atmospheric particulate collected at the monument. S-rich particles are the most abundant particles in the size range < 0.5 μm. High amounts of biogenic particles (K-P-S-rich) were found, especially for particles < 1.0 μm. The chemical, mineralogical and petrographic characteristics of the stratum that holds the monument were studied down to a depth of 20 cm. Two distinctive processes are active at the stone–atmosphere interface. Firstly, a weathering crust (ca. 2 mm thickness), consisting mainly of calcite and gypsum and enriched with Cl^–, K⁺ and NO₃^–, is formed in the rain-sheltered areas of the monument. Secondly, karstic dissolution in the interior of the rock substrate leads to the formation of a hard carbonate crust at the surface of the sculpture. This natural surface hardening leads to a state of ‘auto-conservationˈ of the monument. The atmospheric composition seems to have only a limited influence on the deterioration of the Madara Horseman. Far more important are the micro-climatic conditions and the action of lichens.