Heritage Stone Research Articles

Protection and consolidation of stone heritage by self-inoculation with indigenous carbonatogenic bacterial communities

Enhanced salt weathering resulting from global warming and increasing environmental pollution is endangering the survival of stone monuments and artworks. To mitigate the effects of these deleterious processes, numerous conservation treatments have been applied that, however, show limited efficacy. Here we present a novel, environmentally friendly, bacterial self-inoculation approach for the conservation of stone, based on the isolation of an indigenous community of carbonatogenic bacteria from salt damaged stone, followed by their culture and re-application back onto the same stone. This method results in an effective consolidation and protection due to the formation of an abundant and exceptionally strong hybrid cement consisting of nanostructured bacterial CaCO3 and bacterially derived organics, and the passivating effect of bacterial exopolymeric substances (EPS) covering the substrate. The fact that the isolated and identified bacterial community is common to many stone artworks may enable worldwide application of this novel conservation methodology.

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.

Synthesis, Photocatalytic, and Antifungal Properties of MgO, ZnO and Zn/Mg Oxide Nanoparticles for the Protection of Calcareous Stone Heritage.

More recently, the biological colonization of stone heritage and consequently its biodeterioration has become the focus of numerous studies. Among all microorganisms, fungi are considered to be one of the most important colonizers and biodegraders on stone materials. This is why the development of new antifungal materials requires immediate action. ZnMgO nanoparticles (NPs) have several exciting applications in different areas, highlighting as an efficient antimicrobial agent for medical application. In this research, the application of Zn-doped MgO (Mg1-xZnxO, x = 0.096) NPs obtained by sol-gel method as antifungal coatings on dolomitic and calcitic stones has been explored as a means to develop effective protective coatings for stone heritage. Moreover, the photocatalytic and antifungal activity of Mg1-xZnxO NPs were comparatively studied with single ZnO and MgO NPs. Thus, compared to the MgO and ZnO nanomaterials, the Mg1-xZnxO NPs exhibited an enhanced photocatalytic activity. After UV irradiation for 60 min, 87% methylene blue was degraded over Zn-doped MgO NPs, whereas only 58% and 38% of MB was degraded over ZnO and MgO NPs, respectively. These nanoparticles also displayed a better antifungal activity than that of single pure MgO or ZnO NPs, inhibiting the growth of fungi Aspergillus niger, Penicillium oxalicum, Paraconiothyrium sp., and Pestalotiopsis maculans, which are especially active in the bioweathering of stone. The improved photocatalytic and antifungal properties detected in the Mg1-xZnxO NPs was attributed to the formation of crystal defects by the incorporation of Zn into MgO. The application of the MgO- and Zn-doped MgO NPs as protective coatings on calcareous stones showed important antifungal properties, inhibiting successfully the epilithic and endolithic colonization of A. niger and P. oxalicum in both lithotypes, and indicating a greater antifungal effectiveness on Zn-doped MgO NPs. The use of Zn-doped MgO NPs may thus represent a highly efficient antifungal protection for calcareous stone heritage.

Mapping recession risk for cultural heritage stone in Mexico City due to dry and wet deposition of urban air pollutants

Air pollution is a threat to cultural heritage because it accelerates the natural deterioration of monuments, palaces, churches, and archaeological ruins, which have an irreplaceable value. In the Mexico City Metropolitan Area (MCMA), there are 19 968 buildings registered as archaeological, historic, or artistic monuments. Some are built with calcareous rocks (limestone and marble) but many of them are made with andesite, tezontle and tuff stone. This paper reports for the first time the spatial distribution of the potential risk of deterioration on calcareous rocks in terms of surface recession with regard to Mexican cultural heritage in the MCMA for the base year 2007. The risk estimate was performed using Lipfert’s damage function, only applicable to carbonate stones of medium and low porosity. These include mainly medium/high density limestone and marble. Carrara white marble has a density of 2.69 g cm –3 and a porosity of 0.37%, and limestone has a density of 2.2-2.6 g cm –3 and a porosity of 5-20%. For high porosity (low density) limestone the function would be applicable with a potential under-estimation. In this function, annual recession rate is a function of annual averages of precipitation, pH, and dry deposition of SO 2 and HNO 3 . Data from several meteorological monitoring networks, the MCMA air quality and acid deposition monitoring networks, and a 3D air quality model (MCCM) were interpolated in a GIS in order to obtain map layers for these variables. These overlaid maps were used to apply the Lipfert functions at the specific coordinates of a small sample of relevant historic or artistic monuments. The complexity of climate gradients, wind patterns, and emissions distribution within the Mexico Megacity leads to gradients as large as 50% in estimated recession rates using the Lipfert function at nearby sites made of the same type of building materials. The Comision Ambiental de la Megalopolis (Environmental Commission of the Megacity) divides the MCMA into five sectors. Differences in recession rates between them were, in 1990, as large as those between estimated values for Oviedo, Paris, and Prague in Europe for the period 1980-2000. Recession rates decreased by about 50% from 1990 to 2007, the base year for this report, due to the success of air pollution control actions focused on the protection of public health. Nevertheless, strong recession gradients are still expected for carbonate stone within the MCMA. The recession values reported in this work must be taken as conservative estimates due to the not yet optimal performance of 3D air quality models in urban meteorology and the high degree of uncertainty in modeling emissions inventories. Most notable is the SO 2 emissions inventory. These maps call for a program of experimental determination of recession rates for building materials that comprise a very large part of Mexico’s unique cultural heritage. These maps should also be added to the critical level maps obtained for human exposure, crops, and ecosystems in order to properly estimate the actual cost of air pollution in the MCMA and the area under its influence.

Structural health monitoring of the retrofitting process, characterization and reliability analysis of a masonry heritage construction

In the last decades, heritage constructions (HC) had been rehabilitated and inserted in functional areas of cities, therefore, the necessity for keeping them structurally safe and functional is high. Therefore, the employment of structural health monitoring (SHM) and operational modal analysis (OMA) techniques can be worthy alternatives for structural characterization and safety management. However, in the literature few cases of SHM of HC are reported, and guidelines or recommendations specifically for safety assessment of HC is an effort still undergoing. Thus, the present work describes the strategies for SHM and structural characterization of a Portuguese stone heritage construction, namely Santo Antonio Church and introduces a new approach for heritage assessment so-called Reliability Analysis Based on Vibrational Measures (RABVIM). The results showed that SHM allowed to guarantee the efficiency level of the retrofitting measures carried out, while OMA provided useful information on the structure modal parameters, under operational loading actuation, apart from the data for reliability assessment. Finally, this work demonstrates that RABVIM can be an interesting and useful tool to support the safety assessment of HC.

Oligoamide grafted with perfluoropolyether blocks: A potential protective coating for stone materials

Abstract In order to mitigate the decay phenomena induced by liquid water adsorption and penetration, new protective coating agents with high hydrophobicity, photo-oxidative stability and good solubility in non-toxic solvents are needed. In the present study, a partially fluorinated oligoadipamide bearing pendant PFPE segments (FAD) together with two diamides i.e., ethylenediamide (DC2) and hexamethylenediamide (DC6) incorporating perfluoropolyether (PFPE) segments, were synthesized via condensation reactions. The diamides are only soluble in chlorofluorocarbons, while the oligoadipamide is soluble in alcohols and hydro-alcoholic solvents e.g., ethanol, 2-propanol. The polymerization degree, together with the molecular weight and molecular weight distribution of oligoethylene-adipamide evaluated by 1H NMR spectroscopy, was found very low which allowed to obtain a partially fluorinated amide with a high fluorine content (57%). To determine the protective performance of the new FAD, a series of standard tests were conducted on Lecce stone and Carrara marble samples. Regarding water repellence, compared with a commercial fluoroelastomer tested as a reference material, FAD demonstrated much higher water repellence when applied on Carrara marble samples, and comparable hydrophobic effect when applied on Lecce stone samples. In comparison with the two diamides, tested on Lecce stone, the oligoamide manifested similar protective efficacy with a much less amount applied (15 g/m2 versus 154/150 g/m2). In addition to its high hydrophobicity, FAD also preserved the original vapor permeability and chromatic features of coated surfaces. With these favorable properties, this new oligomeric product is ought to be proposed as protective coating material for stone heritage.

Granites of Salamanca. A perfect example for the recognition of natural stone as a heritage resource and their use in restoration

In the province of Salamanca (Spain) there are several quarries that used to be the source of natural stone used in the construction of historic buildings and that are today recognized by UNESCO as World Heritage Sites. In this study we investigated the granites used in the construction and restoration of the lower ashlars of the walls of different buildings in Salamanca, Alba de Tormes, Ciudad Rodrigo, and Ledesma. The characterization of the different types of granite and their current state of preservation may serve to adopt specific measures for their possible use in the restoration of the architectural heritage of the province if this should become necessary. Despite the variety of materials observed in the lower parts of the buildings (ranging from sandstone to conglomerate to granite), the stone most frequently used was the granite from Los Santos and the Martinamor granite, followed by the vaugneritic granites from Ledesma. In general, the granite materials are in good condition, but the existence of certain pathologies that have given rise to processes of flaking and discoloration of the rock suggests that it will be necessary to make a consistent assessment when deciding about possible actions aimed at replacing materials in these historic buildings. Moreover, the various granites differ from one another, and pieces should not be replaced without perfect identification of the specific type to which they belong. A detailed study of these granites is crucial for the nomination of some of them as candidates for the denomination Global Heritage Stone Resource and the whole set of Salamanca province lithologies as a Global Heritage Stone Province.

Boehmite/methacrylic nano-composites as protective coatings for natural stones: comparison between sunlight and UV photopolymerization cure reaction

The protective properties of two innovative, experimental nano-composite coatings which are mainly intended for the protection of cultural heritage stone artifacts were compared. The decay of artworks, monuments, and buildings made of stone materials is a natural and irreversible process. In order to protect stone artworks and buildings from natural decay, it is necessary to reduce the penetration of water into porous substrates by applying a highly hydrophobic protective coating on the stone surface. The performances of two nano-composite coatings containing an organo-modified boehmite nano-filler, applied on calcareous stone substrates typical of Apulia region (leccese stone, PL and gentile stone, PG), and activated by UV or sunlight radiations, were compared in order to establish the more suitable product for the specific stone substrate.

Evaluation of Preservation Effect by Aquo-Siloxane Method towards Water Permeation and Material Diffusion into Porous Rocks

Various kinds of heritages, such as architectures, statues, grave posts and towers, are made by stone, and they are facing the crisis of weathering. Therefore, it is necessary to give appropriate treatments to keep them in good conditions. Kyushu Research Institute for Cultural Properties Inc. and Kumamoto University introduced a new method, Aquo-Siloxane Method, in order to protect the stone heritages. In this study, preservation effect by Aquo-Siloxane method towards water permeation and material diffusion was verified. Here one-dimensional permeation and diffusion tests were conducted, and the intrinsic permeability and diffusion coefficient of rock samples with and without Aquo-Siloxane treatments were evaluated. As rock samples, 3 types of sandstones and concrete were applied. It was found that the permeability decreased to less than 1/10 to 1/100 of without Aquo-Siloxane treatment, and that the effect gradually developed during more than one year. One-dimensional diffusion tests were also conducted, and the diffusion process in rock samples are visualized by X-ray CT scanner system. It was confirmed internal structures of samples are clearly visualized, and that the diffusion process was also visualized as X-ray CT images. In order to extract the necessary information due to diffusion, image subtraction method was applied to image data. Then, by comparing obtained CT image data and numerical solutions, diffusion coefficients of rock samples with and without Aquo-Siloxane treatments were evaluated. As a result, diffusion coefficients also became smaller by applying Aquo-Siloxane treatments. It is revealed that material movement due to diffusion was also efficiently suppressed by applying Aquo-Siloxane method. Finally, Aquo-Siloxane method was applied to a stone heritage. It was found that no more chippings and cracks were observed and that the heritage has been kept in good condition for at least four years.

The Importance of Geosites and Heritage Stones in Cities—a Review

Geology, as a scientific discipline, is often viewed as most applicable in high mountains or in deserts or coastal areas—or more generally in ‘natural areas’ where rock exposures are most conspicuous—and, therefore, not to be experienced by most visitors and tourists. In contrast, most geoscientists are convinced that geology can be practised on an everyday basis, as it is part of our daily life as a facet of the natural environment that humans have used for 100 s of thousands of years. Even in places where the natural world seems far from its original condition, one can still experience geology. This consideration is of increasing importance, as today, more than half the world’s population lives in towns and cities. In this context, we can still present geology to an interested public through establishing leisure walks, either guiding or using leaflets, easily carried booklets and even web ‘apps’. The style chosen aims to be accessible to a broader public, but crucially, in an urban context, there should always be an aim to demonstrate the relationship between geology and society, as well as architecture and history. Indeed, the realisation of many participants in such activities that building stones can belong to, and provide evidence of, both a natural and a built heritage can be a revelation.

Influence of wavelength on the laser removal of lichens colonizing heritage stone

Laser irradiation of lichen thalli on heritage stones serves for the control of epilithic and endolithic biological colonizations. In this work we investigate rock samples from two quarries traditionally used as source of monumental stone, sandstone from Valonsadero (Soria, Spain) and granite from Alpedrete (Madrid, Spain), in order to find conditions for efficient laser removal of lichen thalli that ensure preservation of the lithic substrate. The samples presented superficial areas colonized by different types of crustose lichens, i.e. Candelariella vitellina, Aspicilia viridescens, Rhizocarpon disporum and Protoparmeliopsis muralis in Valonsadero samples and P. cf. bolcana and A. cf. contorta in Alpedrete samples. A comparative laser cleaning study was carried out on the mentioned samples with ns Q-switched Nd:YAG laser pulses of 1064nm (fundamental radiation), 355nm (3rd harmonic) and 266nm (4th harmonic) and sequences of IR-UV pulses. A number of techniques such as UV-Vis absorption spectroscopy, stereomicroscopy, scanning electron microscopy (SEM) at low vacuum, SEM with backscattered electron imaging (SEM-BSE), electron dispersive spectroscopy (EDS) and FT-Raman spectroscopy were employed to determine the best laser irradiation conditions and to detect possible structural, morphological and chemical changes on the irradiated surfaces.The results show that the laser treatment does not lead to the complete removal of the studied lichen thalli, although clearly induces substantial damage, in the form of loss of the lichen upper cortex and damage to the algal layer. In the medium term these alterations could result in the destruction of the lichen thalli, thus providing a degree of control of the biodeterioration processes of the lithic substrate and reducing the chances of subsequent lichen recolonization.

The effect of frost weathering at the dinosaur tracksite in Seoyu-ri, Hwasun, Korea

Cultural monuments and geological heritage sites composed of natural stone are severely affected by frost weathering in cold regions or during the winter season in mid-altitude regions. The effect also occurs at the dinosaur tracksite in Seoyu-ri, Hwasun, Korea, which is not sheltered. To assess the influence of frost weathering on the tracksite, freeze–thaw experiments were carried out in the laboratory up to 100 cycles, simulating geological and meteorological conditions of the site. The variation on physical properties were measured at a core scale as weathering progressed. The decreases in dry weight, P- and S-wave velocity, and elastic modulus, and the increase in absorption rate and Poisson’s ratio showed the physical deterioration of the specimens. The microstructural properties were also measured using micro-computed tomography (micro-CT) images as weathering progressed. The variation on porosity (especially open porosity), pore size distribution, local thickness, and crack orientation showed the propagation and expansion of the pores and microcracks in rock specimens at a pore scale. Because every measurement was performed using non-destructive methods, the variation on the same specimens can be analyzed continuously. The results showed that frost weathering can cause damage to the tracksites. This research, therefore, suggests the construction of a shelter to maintain the temperature of the tracksite and to prevent groundwater seepage. This research can be applied to assess the effects of frost weathering at other cultural stone heritage or geological heritage sites.

San Pedro Leucogranite from a Coruña, Northwest of Spain: Uses of a Heritage Stone

San Pedro leucogranite from A Coruña, in the Northwest of Spain, has been a building stone widely used in the Middle Ages. Colour, rarity, appearance and petrophysical properties have led to the use of this leucogranite.Monuments such as churches, tombstones and the basement of the Hercules Tower lighthouse, declared a UNESCO World Heritage Site in 2009, make it an ideal candidate for designation as a Global Heritage Stone Resource.

FROM SHOKSHA TO PARIS (THE HISTORY OF QUARRYING, TRANSPORTATION AND CARVING STONE FOR THE SARCOPHAGUS OF NAPOLEON)

The sarcophagus of Napoleon in The Dome des Invalides in Paris is made of quartzite, a unique ornamental stone from Karelia, NW Russia, but not of porphyry or granite. This beautiful stone is similar in colour and structure to famous antique porphyry from Egypt. However, there are no more monoliths left in antique quarries. The authors focus the reader’s attention on evidence for the prospecting and quarrying of quartzite near Shoksha village on the Onega Lake shore, the delivery of monoliths to Paris and their carving. Photographs of the signs of the primary sedimentary genesis of the stone, such as lamination, microfaults and the displacement of the laminae, taken by A. I. Brusnitsyn are presented. J. Touret has revealed the bimodal size distribution of the quartz grains and found that their morphology is typical of the recrystallization of smaller grains subjected to high-temperature metamorphism. In 1846, the writer and journalist Leouzon Le Duke left Paris for Russia to look for and quarry a suitable stone. On arrival in St. Petersburg, he invited the engineer J.-F. Bouyatti to join him as an assistant. Emperor Nicholas I allowed the men to start quarrying without paying the cost of the stone quarried and taxes. France payed all the costs of the starting-up of the quarry, the quarrying operations and the transportation of the blocks (38 m3). It took over three months to transport the blocks on river and sea ships from the Onega Lake shore to Paris. Technical calculations showed that the carving of the hard quartzite would take several years. Therefore, for the first time in history, steam machines driven by monolith-cutting, carving and polishing mechanisms were created. It was a real technological revolution. It took two years to make the sarcophagus; the work was finished by the end of 1853. In the authors’ opinion, Shoksha quartzite can be registered as a world cultural heritage stone.

Higher diversity and abundance of ammonia-oxidizing archaea than bacteria detected at the Bayon Temple of Angkor Thom in Cambodia

Ammonia-oxidizing archaea (AOA) and bacteria (AOB) are two groups of the ammonia-oxidizing microorganisms responsible for conversion of ammonia to nitrite, producing acidity and damaging building materials, including valuable cultural heritage stone structures. In this study, the molecular biomarker of amoA gene of archaea and bacteria was applied in polymerase chain reaction (PCR) amplification and quantitative real-time (RT) PCR (qPCR) to detect the abundance of AOA and AOB at 4 locations (Pond, Entrance, Gallery and Central Tower) of Bayon temple at Angkor Thom, Cambodia. The results showed that both AOA and AOB were positively detected at all locations and the diversity index suggested that AOA were more diverse than AOB. Sequences of AOA were mainly distributed in Group I.1b and few clustered in Group I.1a and Group I.1a-associated, while AOB were all closely related to β-proteobacteria (Nitrosospira). Based on the qPCR results, AOA outnumbered AOB clearly, the gene copy numbers of AOA amoA gene ranged from 1.35 × 106 to 2.52 × 108 copies per gram of dry materials, while, in comparison, AOB amoA gene copy numbers from 6.54 × 105 to 4.52 × 106 copies per gram of dry materials. In addition, the abundance of amoA gene from galleries was the highest than other locations. At gallery section, gene abundance, NH4+ and NO3− agreed well with the intensity of biofilm development. Based on the community and abundance analysis, nitrogen cycling plays an important role in contributing to deterioration of sandstone monuments at Angkor Thom in Cambodia under tropical climate.

Synthesis of TEOS/PDMS-OH/CTAB composite coating material as a new stone consolidant formulation

A new stone consolidant formulation based on tetraethoxysilane (TEOS) and additives such as hydroxyl-terminated polydimethylsiloxane (PDMS-OH) and cetyl trimethyl ammonium bromide (CTAB) has been developed denoted as TEOS/PDMS-OH/CTAB composite coating material. The hydrophobic property, surface morphology, and abilities to resist acid corrosion and salt crystallization weathering have been measured to evaluate the stone protection performance of as-prepared TEOS/PDMS-OH/CTAB composite coating materials. The results demonstrate that the addition of PDMS-OH contributes to improve the hydrophobic properties of sandstones. The addition of CTAB to the siloxane composition results in the formation of superficial protrusions with a micro- and nanoscopic structure and overall alteration of surface morphology and roughness, thus preventing the cracking during the drying process. In addition, after treatment by TEOS/PDMS-OH/CTAB composite coating materials, the sandstone has improved the abilities to resist acid and salt crystallization weathering significantly. These advantages make TEOS/PDMS-OH/CTAB composite coating materials exhibit good comprehensive performance in terms of stone heritage protection.

Heritage Stone 6. Gneiss for the Pharaoh: Geology of the Third Millennium BCE Chephren's Quarries in Southern Egypt

A remarkable campaign of decorative stone quarrying took place in the southwestern Egyptian desert almost 5000 years ago. The target for quarrying was Precambrian plagioclase−hornblende gneiss, from which several life-sized statues of King Chephren (or Khafra) and thousands of funerary vessels were produced. The former inspired George Murray in 1939 to name the ancient quarry site 'Chephren's Quarries.' Almost 700 individual extraction pits are found in the area, in which free-standing boulders formed by spheroidal weathering were worked by stone tools made from local rocks and fashioned into rough-outs for the production of vessels and statues. These were transported over large distances across Egypt to Nile Valley workshops for finishing. Although some of these workshop locations remain unknown, there is evidence to suggest that, during the Predynastic to Early Dynastic period, the permanent settlement at Hierakonpolis (Upper Egypt) could have been one destination, and during the Old Kingdom, another may have been located at pyramid construction sites such as the Giza Plateau (Lower Egypt). Chephren's Quarries remains one of the earliest examples of how the combined aesthetic appearance and supreme technical quality of a rock made humans go to extreme efforts to obtain and transport this raw material on an ‘industrial’ scale from a remote source. The quarries were abandoned about 4500 years ago, leaving a rare and well-preserved insight into ancient stone quarrying technologies. RÉSUMÉUne remarquable campagne d’extraction de pierres décorative a été mené dans le sud-ouest du désert égyptien il y a près de 5000 ans. La roche cible était un gneiss à plagioclase–hornblende, de laquelle ont été tiré plusieurs statues grandeur nature du roi Khéphren (ou Khâef Rê) et des milliers de vases funéraires. C’est pourquoi George Murray, en 1939, a donné au site de l’ancienne carrière le nom de 'Chephren’s Quarries.' On peut trouver près de 700 fosses d’extraction sur le site, renfermant des blocs de roches formés par altération sphéroïdale qui ont été dégrossis avec des outils de pierre pour la production de vases et de statues. Puis ils ont été transportés à travers l’Égypte jusqu’aux ateliers de finition de la vallée du Nil. Bien que la localisation de certains de ces ateliers demeure inconnue, certains indices permettent de penser que, de la période prédynastique jusqu’à la période dynastique précoce, l’établissement permanent à Hiérakonpolis (Haute Égypte) aurait pu être l’une de ces destinations; durant l’Ancien empire une autre destination aurait pu être située aux sites de construction de pyramides comme le Plateau de Giza (Basse Égypte). Les Chephren’s Quarries l’une des plus anciennes exemples montrant comment la combinaison des qualités esthétiques et techniques remarquables de la roche ont incité les humains à consentir de si grands efforts pour extraire et transporter ce matériau brute à une échelle industrielle d’un site éloigné. Les carrières ont été abandonnées il y a environ 4500 ans, nous laissant une fenêtre rare et bien conservé sur des technologies anciennes d’extraction de pierre de taille.Traduit par le Traducteur

Heritage Stone 2. The Dora-Maira Unit (Italian Cottian Alps): A Reservoir of Ornamental Stones Since Roman Times

The Dora-Maira Unit is a geological unit cropping out in the inner part of the Cottian Alps and belonging to the Penninic Domain of the Western Alps (northwestern Italy). It consists of a Paleozoic basement and its Mesozoic carbonate cover, metamorphosed under eclogite facies conditions in the Cenozoic. Due to the complexity of the rock associations and the textural-metamorphic transformations, the Dora-Maira Unit has been a source of ornamental stones over the centuries, and still represents a reservoir of material locally employed for historical and contemporary buildings. Several varieties of orthogneiss, quartzite and marble, derived from the Paleozoic basement and Mesozoic cover, are known by different local names (e.g. Luserna Stone, Borgone and Vaie Stone, Perosa Stone, Bargiolina Quartzite, Foresto and Chianocco Marble).These stones were largely employed during the 17th and 18th centuries for some of the most famous and important monuments in Turin (capital of Piedmont region, northwestern Italy), as well as in the countryside, since Roman times. Some of the materials exploited in the Dora-Maira Unit were also exported to foreign countries: Borgone and Vaie Stone were used for the paving of the Louvre Museum, and Perosa Stone was employed for the construction of the monument of Independence in Lagos, Nigeria. Consequently, the Dora-Maira Unit can be designated as a Global Heritage Stone Province.RÉSUMÉL’Unité Dora-Maira est une unité géologique affleurant dans la partie interne des Alpes Cottiennes; elle appartient au Domaine Penninique des Alpes occidentales (Italie du Nord-Ouest). Elle se compose d'une croûte continentale d’âge Paléozoïque supérieur et de sa couverture carbonatique Mésozoïque, métamorphosées en faciès éclogite pendant le Cénozoïque. En raison de la complexité des associations lithologiques et des transformations métamorphiques et structurelles, l’Unité Dora-Maira a été une source de pierres ornementales au cours des siècles, et encore il représente un réservoir de matériau employé localement pour des bâtiments contemporains et historiques. Plusieurs variétés de gneiss, de quartzite et de marbre, provenant du socle paléozoïque et de la couverture mésozoïque et connues sous différents noms locaux (par exemple Pierre de Luserna, Pierre de Borgone et Vaie, Pierre de Perosa, Bargiolina, marbres de Foresto et Chianocco), étaient largement utilisées pour certains monuments les plus célèbres et importants à Turin (capitale de la région Piémont), au cours des 17ème et 18ème siècles, et dans les alentours de la ville depuis l'époque romaine. Certains des matériaux exploités dans l'Unité Dora-Maira ont été également exportés aux pays étrangers: la Pierre de Borgone et Vaie a été utilisée pour le pavage du Musée du Louvre, et la Pierre de Perosa a été employé en Afrique, à Lagos, au Nigéria, pour la construction du monument de l'indépendance. Par conséquent, l'Unité Dora-Maira peut être indiquée comme une Pierre Province du patrimoine mondial.

Heritage Stone 1. Repair and Maintenance of Natural Stone in Historical Structures: The Potential Role of the IUGS Global Heritage Stone Initiative

Natural stone has been used for millennia in many historically and culturally important structures. It inevitably undergoes weathering from natural processes and damage from human activities. Deterioration affects both ornamental features and main structural members of constructions, ultimately requiring repair and maintenance, or causing loss of the structure altogether. Stone similar to the original should generally be used for repairs, but if that is impossible a closely similar material is required. Use of inappropriate stone or treatment with incompatible mortars can be aesthetically unsightly or have structurally and financially damaging consequences. Such use typically arises because of a lack of information and awareness among commissioners and specifiers of works, along with budget constraints leading to selection of cheaper alternatives. Even some World Heritage Sites have suffered. Selected examples from Western Europe illustrate these problems. The Global Heritage Stone initiative has been launched to improve recognition of the internationally most important heritage stones, promote their proper use in construction, maintenance and repair, and to stress the need to safeguard important stone resources for future use.RÉSUMÉLa pierre naturelle a été utilisée depuis des millénaires dans de nombreuses structures importantes historiquement et culturellement. Inévitablement cette pierre s’altère sous l’effet de processus naturels et de dommages causés par les activités humaines. Cette détérioration affecte aussi bien les éléments ornementaux que les principaux éléments structuraux des constructions, ce qui, éventuellement nécessite réparation et entretien, ou alors peut entraîner la perte de la structure. Une pierre semblable à l'originale doit généralement être utilisée pour des réparations, ou alors un matériau très similaire est requis. L’utilisation d’une pierre inappropriée ou un traitement avec des mortiers incompatibles peut être esthétiquement disgracieux ou avoir des conséquences structurellement et financièrement préjudiciables. Cette utilisation erronée est typiquement le résultat d’un manque d'information et de sensibilisation des commissaires et des rédacteurs du cahier des charges, ainsi que de contraintes budgétaires conduisant au choix d’options moins coûteuses. Et même, certains sites du patrimoine mondial en ont souffert. Des exemples choisis de l'Europe de l’ouest illustrent ces problèmes. L'initiative du patrimoine mondial de la pierre de taille lancée pour améliorer la conscience à l'échelle internationale des principales pierres du patrimoine, promouvoir leur utilisation correcte dans la construction, leur entretien et leur réparation, et souligner la nécessité de préserver les ressources importantes en pierre pour les besoins à venir. Traduit par le Traducteur

Heritage Stone 5. Silicified Granites (Bleeding Stone and Ochre Granite) as Global Heritage Stone Resources from Ávila, Central Spain

Silicified granites were used to build the Romanesque monuments in the city of Ávila, Spain. The building stones comprise two types of granite based on their technical properties and colour: Bleeding Stone (Piedra Sangrante) and Ochre Granite (Caleño). They were used as a facing stone in the city´s Romanesque monuments of the 12th century (e.g. the cathedral and church of San Pedro), and the famous city walls that constitute the best example of military Romanesque Spanish architecture. During the Gothic and Renaissance periods of the 13th and 15th centuries, silicified granites were used mainly to build ribbed vaults, the voissoirs of the arches, and elements of the windows in the monuments of Ávila. Silicified granites are found in the intermediate and upper part of a complex palaeoweathering zone or mantle developed on the Iberian Hercynian Basement which underlies much of the western Iberian Peninsula. The silicification occurred during tropical conditions in the Mesozoic. The weathered mantle was truncated by Alpine tectonic movements during the Tertiary, and its remnants were unconformably overlain by more recent sediments in the western and southern part of the Duero Basin and along the northern edge of the Amblés Valley graben. The historical, and now protected, quarry is located in a village called La Colilla, about 5 km from the city of Ávila. Currently, this stone is exploited only for restoration work performed in the city, for example the Walls of Ávila, and the church of San Pedro. The resource is limited and being depleted, so the stone will be scarce in the near future. Consequently, these silicified granites should be recognized as a Global Heritage Stone Resource. The specific technical properties of these stones and their historic use, decay patterns, durability, and suitability for conservation treatments combine to support its designation as a Global Heritage Stone Resource.RÉSUMÉDes granites silicifiés ont été utilisés pour construire les monuments romans dans la ville d’Ávila, en Espagne. Les pierres de construction comprennent deux types de granite selon leurs propriétés techniques et leur couleur : Bleeding Stone (Piedra sangrante) et Ochre Granite (Caleño). Ils ont été utilisés comme pierre de revêtement de monuments romans du 12ème siècle de la ville (par exemple la cathédrale et de l'église de San Pedro), et pour les célèbres remparts de la ville qui constituent le meilleur exemple de l'architecture espagnole romane militaire. Durant les périodes gothique et Renaissance des 13e et 15e siècles, les granites silicifiés ont été utilisés principalement pour construire des croisés d'ogives, des voussoirs d’arcs et des éléments de fenêtres des monuments d’Ávila. Les granites silicifiés se trouvent dans la partie intermédiaire et supérieure d'une zone complexe de paléo-altération ou de manteau développée sur le socle ibérique hercynien qui supporte une grande partie de la péninsule ibérique occidentale. La silicification s’est produite dans des conditions tropicales au Mésozoïque. Le matériau mantélique altéré a été tronqué par des mouvements tectoniques alpins au cours du Tertiaire, et ses restes ont été recouverts en discordance par des sédiments plus récents dans la partie ouest et sud du bassin de Duero, et le long de la bordure nord de la vallée en graben d’Amblés. L’ancienne carrière, maintenant protégée, est située dans un village appelé La Colilla, à environ 5 km de la ville d’Ávila. Actuellement, cette pierre est exploitée uniquement pour les travaux de restauration effectués dans la ville, par exemple les murs d’Ávila, et l'église de San Pedro. La ressource est limitée et en voie d'épuisement, de sorte que la pierre sera rare dans un proche avenir. Par conséquent, ces granites silicifiés devraient être reconnus en tant que pierre du Patrimoine mondial des ressources en pierre. Les propriétés techniques spécifiques de ces pierres et leur valeur historique, leurs modes de désintégration, leur durabilité et leur pertinence pour la conservation patrimoniale justifient leur désignation en tant que roche du Patrimoine mondial des ressources en pierre. Traduit par le Traducteur