Head of the Department of Conservation and Built Heritage and Deputy Dean of the Faculty for the Built Environment, University of Malta. Professor and researcher on conservation of building materials, with a specific interest in historic and traditional buildings and archaeological sites.
Working Towards a Sustainable Past. ICOM-CC 20th Triennial Conference Preprints, Valencia, 18–22 September 2023, ed. J. Bridgland. Paris: International Council of Museums., 2023
The sheltering of an archaeological site is a reversible, preventive measure that needs to be bas... more The sheltering of an archaeological site is a reversible, preventive measure that needs to be based on sound scientific data. This paper focuses on the studies that led to the sheltering of three of the UNESCO-listed Prehistoric Megalithic Structures on the Maltese Islands, including data collection and evaluation before and after the sheltering. Scientific investigations of these sites commenced in 1985 and included accurate documentation, environmental monitoring and limited sampling and analyses. Within the last four years, targeted studies have used an entirely non-invasive approach to evaluate the performance of one of the open-sided shelters, erected in 2009 over the Mnajdra site. Understanding both the state of conservation of the megaliths and the causes of their deterioration is of primary importance, as is evaluating the impact of the shelters on the micro-environment of the site. Thermal imaging, on-site chemical analyses and environmental studies are being carried out, with wind data in particular leading to the development of a 3D wind-flow numerical model. These data will be crucial in future decisions regarding conservation measures for the megaliths, including whether the preventive approach at the heart of the original decision is effective and whether any changes need to be made to the current strategy to ensure the continued preservation of these fragile sites.
The behaviour of traditional roofs affects issues relating to sustainability, zero-carbon targets... more The behaviour of traditional roofs affects issues relating to sustainability, zero-carbon targets, and Urban Heat Island (UHI) effect. This paper discusses an innovative approach towards understanding the behaviour of porous, and other types, of roofs in Malta in relation to temperature and moisture characteristics, and to project this behaviour onto a changing climate, predicted to be hotter and drier. The new methodology is being trialled on four roof types, on historic buildings, the innovation being the use of data from co-temporal Earth Observations (EO) and Unmanned Aerial Vehicles (UAVs), in conjunction with in-situ data. This research is helping to develop a new application for Remote Sensing in Cultural Heritage; results should enable recommendations for sustainable use of traditional roof-building techniques. The initial results show that the traditional roof has different (reflective and emissive) properties from the hybrid roof, that are being detected from space, complemented with UAV, hand-held thermal camera and in-situ measurements. These results are preliminary; satellite images for spring/early summer and midsummer and the corresponding UAV images are expected to provide more conclusive information. These promising results should enable the proof-of-concept to progress onto a larger number and greater variety of roof types, even in other Mediterranean countries.
Climate change, as revealed by gradual changes in temperature, precipitation, atmospheric moistur... more Climate change, as revealed by gradual changes in temperature, precipitation, atmospheric moisture, and wind intensity, as well as sea level rise and changes in the occurrence of extreme events, is already affecting cultural heritage sites. Accordingly, there is a rapidly increasing body of research reporting on the impacts of climatic stressors on cultural heritage and on the assessment of climate change impacts on cultural heritage assets. This review synthesizes the international literature on climate change impacts on tangible cultural heritage by developing hazard‐impact diagrams focusing on the impacts of gradual changes in climate on: (1) the cultural heritage exposed to the outside environment, (2) the interiors of historical buildings and their collections, and (3) a third diagram associated with climate change and the impacts due to sudden changes in the natural physical environment (e.g., storm surges, floods and landslides, wildfire) in addition to sea level rise, permafrost thawing, desertification and changes in the properties of the oceans. These diagrams, which depict the relationships between various stressors and their impacts on cultural heritage, will allow other researchers, stakeholders, and potentially decision makers to determine the potential impacts of climate change on a specific cultural heritage asset without a separate examination of the literature. This review thus provides the current state‐of‐the‐art on the impacts of climate change on the tangible, built heritage, that is, monuments, archaeological sites, historical buildings, as well as their interiors and the collections they hold, highlights the limitations of previous research, and provides recommendations for further studies.
Structure from Motion (SfM) photogrammetry, on-site hardness and water 25 absorption tests, and p... more Structure from Motion (SfM) photogrammetry, on-site hardness and water 25 absorption tests, and petrographical and porosimetric analyses on targeted samples were carried out on representative areas within six different locations of Maltese fortifications affected by salt weathering. The objective was to quantify the limestone loss over the last half-millennium and to attempt to identify the controlling factors of durability. The results highlight the existence of a two-rate weathering regime within the Miocene Globigerina Limestone which is the main building stone of the Maltese Islands. With a median stone recession of 1.4 mm/century, the subtype locally called Franka has resisted atmospheric aggression on average 36 times better than the Soll subtype (median stone recession of 50 mm/century). The Oligo-Miocene Coralline Limestone has also resisted well, with a stone recession of on average 1.3 mm/century. Two main controls of the varying durability of these limestones have been identified. First, the water uptake capacity of the least durable, already weathered limestone (Soll) is two to three times higher than that of the weathered but more resistant Franka and Coralline Limestone (6.3 g.m-².s-1 against 2.5 g.m-².s-1). Second, there is a marked difference in cohesiveness between these limestones. Whereas the weathered, susceptible Soll facies is poorly-cemented or microcracked, the exposed durable Franka displays an abundant micritic and microsparitic matrix. The statistical relationship between durability and surface hardness is not straightforward, and other controls such as the clay content of limestones should be explored. Investigating a larger number of sites would allow the refining of the limestone durability scale inferred from the present study.
Since their excavation, a number of the sites listed as part of "The Megalithic Temples of Malta"... more Since their excavation, a number of the sites listed as part of "The Megalithic Temples of Malta" inscription on the UNESCO World Heritage list have been afflicted by material and structural problems, including collapses. Therefore, three of these sites, the Ħaġar Qim, Mnajdra and Tarxien Temples, were protected by open-sided shelters, to address some of the principal causes of deterioration (e.g. direct rainfall, surface weathering, thermal stress). Environmental monitoring, condition assessments and biological surveys of the three sites took place before and after sheltering and are still in progress. To understand how the shelters are affecting these structures, a research programme has started aimed at analysing, through Computational Fluid Dynamics (CFD), the environmental data collected over a period of more than ten years. The aim of using CFD on the Temples is to provide detailed information on how different environmental conditions can affect the sites. For the CFD, macro and meso scale approaches will be used. The macroscale model represents the regional environment, including the all-terrain features around the Temples. Mesoscale modelling represents the Temple structures in a more detailed way. The final goal is to find confident correlations between CFD, and representative areas selected within the Temples showing particular deterioration patterns. All this information will be integrated with the results of in situ analyses to identify the causes of material deterioration and possibly mitigate against them.
Malta is known for its limestone megalithic temples of which many are inscribed on the UNESCO Wor... more Malta is known for its limestone megalithic temples of which many are inscribed on the UNESCO World Heritage List. A variation of this limestone was historically, and until very few years ago, a primary building material in Malta. The temples are subject to various environmental influences which until recently have led to several collapses due in part to serious stone surface and infill loss. As a protection measure, open-sided shelters have been built over three of these temples. This work assesses the degrading influence of air pollution (nitrogen dioxide, ozone, particle matter, sulfur dioxide, and acidity in rain) on the temples, in combination and comparison with the influence of other environmental factors (relative humidity, temperature, precipitation, moisture, sea salt, wind) and in this respect evaluates the potential protective effect of the shelters. The variation in air pollution weathering of limestone exposed outdoor in Malta was calculated by exposure-response functions from the ICP-materials programme and compared with measured values, and its contribution to the deterioration of the temples was evaluated. The difference between urban and rural locations in Malta, in the first year of atmospheric chemical weathering of limestone due to air pollution, was found to be about one micrometer loss of stone surface. This is probably less than the annual variations due to the influence of natural climatic factors, and small compared to the present annual variations in continental Europe. The deposition of sea salt and presence of salts on and in the limestone megaliths and changes in salt-crystallization events due to relative humidity fluctuations, inside and outside the shelters, will account for more of the variations in the first year of weathering of Globigerina limestone than variations in air pollution. The deterioration will also be related to temperature (including condensation events), wind parameters and rainfall, as well as ground water replenished from areas beyond the shelter.
The use of inhibition chemicals holds the prospect of an efficient strategy to control crystalliz... more The use of inhibition chemicals holds the prospect of an efficient strategy to control crystallization in porous materials, thereby potentially contributing to the prevention or mitigation of the salt decay phenomenon in modern as well as historical building materials in a more sustainable manner. In this review, we first provide an essential background on the mechanism of salt crystallization and on the factors influencing this phenomenon; next, we illustrate the mechanism at the basis of the action of crystal growth inhibitors, and critically discuss the major advances in the development of different families of inhibitors, particularly focusing on their influence on salt transport and crystallization within the structure of porous media. Specifically, correlations between the crystallization inhibition processes in porous materials and variables, such as porous substrate composition and properties, contaminant salt type and concentrations, microclimatic conditions, inhibiting solution concentration and properties, and application methods, will be highlighted. Environmental aspects, limitations, and problems associated with some inhibition chemicals are also taken into account. Finally, a survey and a discussion on the most representative experimental techniques and instrumentation available to assess qualitatively and quantitatively the inhibitor effectiveness, as well as recently developed modelling tools are given out.
Ing. Arch. Gennaro Tampone passed away in February 2018, after a lifetime dedicated to studies on... more Ing. Arch. Gennaro Tampone passed away in February 2018, after a lifetime dedicated to studies on historic structures, their technology and their conservation. Whereas his studies on the conservation of ancient wooden structures won him international acclaim, his decades-long research on the Prehistoric Megalithic Temples of the Maltese Islands is possibly less well known. But it is no less significant. Ing. Tampone led and inspired a multi-disciplinary team of researchers and students – when multi-disciplinarity was not yet considered vital in the field of architectural or archaeological conservation – working in the field, in archives and in laboratories, to elucidate the mode of construction of these unique UNESCO inscribed structures, with the ultimate aim of their conservation. His many publications on the subject, also seminal papers in the Bollettino Ingegneri, attest to his firm belief in the intrinsic value of surveying, documenting, photographing and recording before trying to conserve, and to understanding underlying technologies and conservation issues. He was also a firm believer in the importance of the dissemination of information and the essential role of teaching and imparting knowledge. His sterling contribution to a general awareness, also amongst the archaeological community, of the great importance of the Temples as architectural forms in their own right, and as part of a “network” of Mediterranean megalithic and similar constructions, the discovery of the sophistication of the mode of construction of these early structures, the direct relation between materials and mode of construction, and above all the significance and validity of the contemporary architectural “models” found within the Temples have all resulted in a legacy which will not be forgotten.
The main building stone in the Maltese Islands is the Globigerina Limestone, of which the Lower m... more The main building stone in the Maltese Islands is the Globigerina Limestone, of which the Lower member is commonly used. This occurs in two types, the durable franka and the more easily weathered soil. Two types of fresh franka (bajda (white) and safra (yellow)), as well as fresh soli stone blocks, were obtained, based on the identification by quarry owners. Their designation was confirmed by geochemistry. Physical and mechanical properties of the three were investigated, including uniaxial compressive strength, water absorption by capillarity, permeability and porosimetry. Porosimetry results confirmed outcomes of previous research work. Soli was found to have a lower overall porosity, but a high percentage of small pores with practically no large pores. Some of the tested stones were then treated with a non-toxic phospho-organic compound containing carboxylic moieties as a salt inhibitor and the corresponding non-phosphorylated compound.
In book: in N.C. Vella, A.J. Frendo & H.C.R. Vella (eds), The Lure of the Antique. Essays on Malta and Mediterranean Archaeology in Honour of Anthony Bonanno, ISBN 978-90-429-3617-1.Publisher: Peeters Publishers, 2018
PREAMBLE In 1991, Prof. Anthony Bonanno and the current author wrote a paper entitled, “The deter... more PREAMBLE In 1991, Prof. Anthony Bonanno and the current author wrote a paper entitled, “The deterioration of cultural property by airborne pollutants: A case study of a Mediterranean Island”.1 This paper was presented at the European University Centre for Cultural Heritage, Ravello, Italy, as part of the Round Table on Airborne Particles: Their Negative Effects on the Cultural Heritage and its Environment. In the twenty-first century, earlier concerns on air pollution effects on cultural heritage have widened to encompass the effects of global climate change on cultural heritage. “Climate Change and Cultural Heritage” was the theme of a number of doctoral courses held in the Ravello Centre between 2009 and 2013. Within this series of courses, in 2013 the present author was invited to give a lecture on adaptation strategies for archaeological sites in connection with climate change. The current paper, which celebrates Prof. Bonanno’s lifetime academic achievements, is based on the contextual information gathered in preparation for that lecture, and includes the expected effects on a local case study, the Megalithic Temples of Malta. The paper on adaptation has been published by the Ravello European University Centre in a book entitled, Cultural Heritage from Pollution to Climate Change to Global Change.
Abstract: Numerous papers included within the broad subject of geomaterials have been published i... more Abstract: Numerous papers included within the broad subject of geomaterials have been published in QJEGH over the past 50 years. These have been compiled and divided here into three main categories: aggregates, building stone and earthworks. The aim of this review is to provide a comprehensive summary of the relevant papers published in QJEGH with a view to identifying the main areas of interest historically, now and in the future. Some clear trends are evident from the survey and review; for example, there has been a steady interest in building stone and in particular its deterioration, a decline in papers on earthworks and an increase in those on ground improvement (also covered here). It is also noted that methods of characterizing geomaterials are becoming more sophisticated with advancing technology. The review makes relevant links with other Special Publications from the Geological Society, including also Engineering Geology Special Publications.
Journal of Civil Engineering and Architecture 11 (2017) 175-183 , 2017
Ammonium oxalate treatment, previously extensively studied on limestone in the laborato... more Ammonium oxalate treatment, previously extensively studied on limestone in the laboratory, was applied to powdering historical stonework (limestone) situated on the shoreline in the Mediterranean Island of Malta. This paper presents the results obtained from onsite testing that aimed at evaluating the treatment in terms of its aesthetic performance, the depth of treatment, the mechanical properties of the consolidated stone and the influence on water transport. To this end, the testing program included colorimetry, DRMS (drilling resistance measurement system) and water absorption through the contact sponge method. This study is Part One of the final phase of a wider research program which included two previous phases progressing from treating this same very porous stone type in a laboratory-based controlled environment to uncontrolled site conditions, seeking to quantify this treatment’s effectiveness in the field. Results showed that onsite consolidation was achieved and that although some changes in colour and water absorption were brought about by the treatment, these were within acceptable tolerance limits. Besides carrying out these treatments and evaluations directly on the coast, this study anticipates further studies which will look at rural and urban sites where the types and concentrations of salts are expected to be different.
Bulletin of Engineering Geology and the Environment, 2015
The millenary use of Lower Globigerina Limestone (LGL) as the main building stone of the Maltese ... more The millenary use of Lower Globigerina Limestone (LGL) as the main building stone of the Maltese Islands is testimony to the importance of this resource to the local building industry. Today, the pressing need to conserve Malta’s rich patrimony of archaeological/historical masonry buildings and structures drives research in this field, particularly in view of the observed variable durability of this stone type. LGL has been described as a moderately weak calcarenite characterised by a predominance of calcite (86–99 %) and high porosity. In theory, these physical properties should make this type of stone particularly susceptible to deterioration involving (a) mechanisms of capillary salt-laden moisture accumulation and movement together with (b) thermodynamic changes in soluble salts during dissolution and crystallisation cycles. The study reported here forms part of a wider research programme aimed at characterising this resource. In this work, we assessed the durability of the LGL in a temperate Mediterranean climate characterised by two main factors, namely (i) a salt-laden marine environment and (ii) relatively short spans of heavy precipitation alternated with longer periods of virtual drought. The main aim of the study was to analyse macro/microporosity variations and minute, yet quantifiable, fluctuations in minor geochemical constituents of the stone with respect to observed weathering characteristics and accelerated crystallisation damage test results. This was achieved through systematic sampling and testing of retrieved core samples extracted from dimension-stone quarrying areas in Malta.
The purpose of this paper is to review the performance of the protective shelters installed over ... more The purpose of this paper is to review the performance of the protective shelters installed over three archaeological sites in Malta over the past decade, and to draw some key lessons learnt that may be useful to others when considering whether to adopt a similar solution. The conservation threats to the Megalithic Temples of Malta are introduced and defined—these range from material issues (loss of surface) to structural issues (cracking and dislodgement of stones leading to structural instability and collapses). Causes identified specifically included fluctuating environmental conditions: wetting and drying cycles and thermal fluctuations, combined with the salt-laden Mediterranean island environment. The recognition during the late twentieth century of these issues as key factors in the deterioration of these structures, and the strategy that was developed in response, are outlined. A key component of this strategy was the installation of protective shelters over three of the main megalithic sites. The process through which the design requirements for the shelters were defined is reviewed. The performance of the shelters is then examined, through a critical review of unpublished reports and published studies. An evidence-based summary of the beneficial effects of the shelters is provided, and the possibility of any harmful effects discussed. A number of lessons learnt through this process are then identified. One key lesson is that the microenvironment in a newly-sheltered site is at a transitional stage that does not necessarily reflect longer-term trends, which therefore require long-term monitoring to be understood. The choice and number of environmental parameters to be monitored need to be informed by a careful consideration of their sustainability, both in terms of equipment and human resources. Any monitoring programme, however well-designed, needs to be open to re-evaluation and revision where needed. As more experience and data are accumulated from different sheltering projects, it will become more feasible to establish performance indicators in advance of a sheltering intervention, on the basis of which to evaluate its performance. The experience of these projects is then used to inform a checklist of key considerations for anyone considering whether to shelter an archaeological site. The foremost consideration is that every site requires a site-specific strategy tailored to its needs. The decision whether a shelter is desirable, and what its performance requirements should be, may only be taken in the context of such a strategy. This paper should help define the parameters for such a decision to take place.
The Maltese Megalithic Temples, constructed between the mid-fourth and mid-third millennia BC, ar... more The Maltese Megalithic Temples, constructed between the mid-fourth and mid-third millennia BC, are unique and are amongst the oldest stone buildings of such complexity in the world. They are of great local and international significance, embodying symbolic, educational and recreational values. These Temples are currently suffering from a series of severe problems associated with the deterioration of materials as well as structural problems, seen in a number of serious collapses in recent years. In 2000, it was decided that these vulnerable prehistoric structures needed to be protected from the direct impact of environmental factors by means of a temporary, open-sided shelter, conceived as a large parasol designed to be as light as possible, in visual as well as in physical terms. The erection of two of these shelters took place during 2008–2009. The performance of the shelters is currently being assessed by environmental monitoring which already indicates an improvement in conditions beneath the shelters when compared to conditions on site before sheltering.
The Lower Globigerina Limestone of the Maltese Islands is here being proposed for nomination as a... more The Lower Globigerina Limestone of the Maltese Islands is here being proposed for nomination as a “Global Heritage Stone Resource”. This stone, continuously used for building and sculpture for 6000 years, is well suited to fit this global designation as it is not only of great local cultural, historic and economic importance, but it is also the building stone used in construction of the UNESCO, and hence internationally recognized, World Heritage city of Valletta, as well as the UNESCO-listed Prehistoric Megalithic Temples of the Maltese Islands. The stone was also exported to several European and North African countries especially in the early 20th century. The entire range of archaeological remains and historic architecture which cover the Maltese Islands have been built in this stone, and encompass innumerable palaces and churches, including the fortified cities of Valletta, Mdina (the old capital of Malta), the Three Cities on the Grand Harbour and the Citadel of Gozo, as well as the vernacular architecture ubiquitous within the village cores all over the Islands. The soft limestone has also been widely used over the millennia for elaborate and extensive sculptural motifs. Practically the only natural resource of the Islands, it continues to be quarried today, and is used not only for new construction, but also for the regular restoration of Malta’s great and imposing architectural heritage, remaining thus an important pillar of the Maltese economy.
Two of the seven prehistoric megalithic Temples of the Maltese Islands inscribed on the UNESCO Wo... more Two of the seven prehistoric megalithic Temples of the Maltese Islands inscribed on the UNESCO World Heritage List were covered by a temporary open-sided shelter in 2009. This was to protect the Temples from environmental factors, primarily direct rainfall and insolation, which were considered as primary causes of deterioration of both the materials and the structures. The sheltering was preceded by an intense environmental monitoring campaign which lasted for one year, and which was then partially continued even after the sheltering. This paper, which evaluates the changes in environmental conditions both before and after sheltering, concludes that the advantages of the shelter far outweigh the disadvantages. Caution is however advocated in the case of noted disadvantages, such as salt, dust and pollution accumulation on the now protected megaliths, which should continue to be carefully monitored for any possible deleterious effects. Recommendations are also given for maintenance actions which can prevent these events from negatively affecting the state of conservation of the megaliths. These include the dry, soft regular brushing of the megaliths, and the surrounding ground, to remove accumulated salts which can cause the limestone to deteriorate if reabsorbed back into the porous stone on occasions when condensation events, which have been detected during the monitoring campaign even after the sheltering, occur.
Climate change varies from temperature increases, to changes in humidity cycles, to increased fr... more Climate change varies from temperature increases, to changes in humidity cycles, to increased frequency and severity of extreme events. The known and predicted effects of this change on the archaeological heritage, both that which is known and that which is still buried, will be summarised in this paper. A synopsis of the main reports and recommendations by UNESCO and ICOMOS, the two main international players where the safeguarding of heritage properties are concerned, will be given, with special emphasis on how these affect archaeological sites, and how these measures can actually be put into practice. Finally, current actions for the conservation of a World Heritage site may be affected by climate change – a case study – will be discussed.
Le changement climatique varie d'augmentation de la température, de changements dans les cycles d'humidité, à l'augmentation de la fréquence et de la gravité des événements extrêmes. Les effets connus et prévus de ce changement sur le patrimoine archéologique, à la fois ce qui est connu et ce qui est encore enfouis, seront résumés dans le présent document. Un résumé des principaux rapports et recommandations de l'UNESCO et de l'ICOMOS, les deux principaux acteurs internationaux où la sauvegarde des biens du patrimoine sont concernés, sera donnée, avec un accent particulier sur la façon dont celles–ci affectent les sites archéologiques, et comment ces mesures peuvent effectivement être mis en pratique. Enfin, les actions en cours pour la conservation d'un site du patrimoine mondial peuvent être affectés par le changement climatique – une étude de cas – seront discutés.
Working Towards a Sustainable Past. ICOM-CC 20th Triennial Conference Preprints, Valencia, 18–22 September 2023, ed. J. Bridgland. Paris: International Council of Museums., 2023
The sheltering of an archaeological site is a reversible, preventive measure that needs to be bas... more The sheltering of an archaeological site is a reversible, preventive measure that needs to be based on sound scientific data. This paper focuses on the studies that led to the sheltering of three of the UNESCO-listed Prehistoric Megalithic Structures on the Maltese Islands, including data collection and evaluation before and after the sheltering. Scientific investigations of these sites commenced in 1985 and included accurate documentation, environmental monitoring and limited sampling and analyses. Within the last four years, targeted studies have used an entirely non-invasive approach to evaluate the performance of one of the open-sided shelters, erected in 2009 over the Mnajdra site. Understanding both the state of conservation of the megaliths and the causes of their deterioration is of primary importance, as is evaluating the impact of the shelters on the micro-environment of the site. Thermal imaging, on-site chemical analyses and environmental studies are being carried out, with wind data in particular leading to the development of a 3D wind-flow numerical model. These data will be crucial in future decisions regarding conservation measures for the megaliths, including whether the preventive approach at the heart of the original decision is effective and whether any changes need to be made to the current strategy to ensure the continued preservation of these fragile sites.
The behaviour of traditional roofs affects issues relating to sustainability, zero-carbon targets... more The behaviour of traditional roofs affects issues relating to sustainability, zero-carbon targets, and Urban Heat Island (UHI) effect. This paper discusses an innovative approach towards understanding the behaviour of porous, and other types, of roofs in Malta in relation to temperature and moisture characteristics, and to project this behaviour onto a changing climate, predicted to be hotter and drier. The new methodology is being trialled on four roof types, on historic buildings, the innovation being the use of data from co-temporal Earth Observations (EO) and Unmanned Aerial Vehicles (UAVs), in conjunction with in-situ data. This research is helping to develop a new application for Remote Sensing in Cultural Heritage; results should enable recommendations for sustainable use of traditional roof-building techniques. The initial results show that the traditional roof has different (reflective and emissive) properties from the hybrid roof, that are being detected from space, complemented with UAV, hand-held thermal camera and in-situ measurements. These results are preliminary; satellite images for spring/early summer and midsummer and the corresponding UAV images are expected to provide more conclusive information. These promising results should enable the proof-of-concept to progress onto a larger number and greater variety of roof types, even in other Mediterranean countries.
Climate change, as revealed by gradual changes in temperature, precipitation, atmospheric moistur... more Climate change, as revealed by gradual changes in temperature, precipitation, atmospheric moisture, and wind intensity, as well as sea level rise and changes in the occurrence of extreme events, is already affecting cultural heritage sites. Accordingly, there is a rapidly increasing body of research reporting on the impacts of climatic stressors on cultural heritage and on the assessment of climate change impacts on cultural heritage assets. This review synthesizes the international literature on climate change impacts on tangible cultural heritage by developing hazard‐impact diagrams focusing on the impacts of gradual changes in climate on: (1) the cultural heritage exposed to the outside environment, (2) the interiors of historical buildings and their collections, and (3) a third diagram associated with climate change and the impacts due to sudden changes in the natural physical environment (e.g., storm surges, floods and landslides, wildfire) in addition to sea level rise, permafrost thawing, desertification and changes in the properties of the oceans. These diagrams, which depict the relationships between various stressors and their impacts on cultural heritage, will allow other researchers, stakeholders, and potentially decision makers to determine the potential impacts of climate change on a specific cultural heritage asset without a separate examination of the literature. This review thus provides the current state‐of‐the‐art on the impacts of climate change on the tangible, built heritage, that is, monuments, archaeological sites, historical buildings, as well as their interiors and the collections they hold, highlights the limitations of previous research, and provides recommendations for further studies.
Structure from Motion (SfM) photogrammetry, on-site hardness and water 25 absorption tests, and p... more Structure from Motion (SfM) photogrammetry, on-site hardness and water 25 absorption tests, and petrographical and porosimetric analyses on targeted samples were carried out on representative areas within six different locations of Maltese fortifications affected by salt weathering. The objective was to quantify the limestone loss over the last half-millennium and to attempt to identify the controlling factors of durability. The results highlight the existence of a two-rate weathering regime within the Miocene Globigerina Limestone which is the main building stone of the Maltese Islands. With a median stone recession of 1.4 mm/century, the subtype locally called Franka has resisted atmospheric aggression on average 36 times better than the Soll subtype (median stone recession of 50 mm/century). The Oligo-Miocene Coralline Limestone has also resisted well, with a stone recession of on average 1.3 mm/century. Two main controls of the varying durability of these limestones have been identified. First, the water uptake capacity of the least durable, already weathered limestone (Soll) is two to three times higher than that of the weathered but more resistant Franka and Coralline Limestone (6.3 g.m-².s-1 against 2.5 g.m-².s-1). Second, there is a marked difference in cohesiveness between these limestones. Whereas the weathered, susceptible Soll facies is poorly-cemented or microcracked, the exposed durable Franka displays an abundant micritic and microsparitic matrix. The statistical relationship between durability and surface hardness is not straightforward, and other controls such as the clay content of limestones should be explored. Investigating a larger number of sites would allow the refining of the limestone durability scale inferred from the present study.
Since their excavation, a number of the sites listed as part of "The Megalithic Temples of Malta"... more Since their excavation, a number of the sites listed as part of "The Megalithic Temples of Malta" inscription on the UNESCO World Heritage list have been afflicted by material and structural problems, including collapses. Therefore, three of these sites, the Ħaġar Qim, Mnajdra and Tarxien Temples, were protected by open-sided shelters, to address some of the principal causes of deterioration (e.g. direct rainfall, surface weathering, thermal stress). Environmental monitoring, condition assessments and biological surveys of the three sites took place before and after sheltering and are still in progress. To understand how the shelters are affecting these structures, a research programme has started aimed at analysing, through Computational Fluid Dynamics (CFD), the environmental data collected over a period of more than ten years. The aim of using CFD on the Temples is to provide detailed information on how different environmental conditions can affect the sites. For the CFD, macro and meso scale approaches will be used. The macroscale model represents the regional environment, including the all-terrain features around the Temples. Mesoscale modelling represents the Temple structures in a more detailed way. The final goal is to find confident correlations between CFD, and representative areas selected within the Temples showing particular deterioration patterns. All this information will be integrated with the results of in situ analyses to identify the causes of material deterioration and possibly mitigate against them.
Malta is known for its limestone megalithic temples of which many are inscribed on the UNESCO Wor... more Malta is known for its limestone megalithic temples of which many are inscribed on the UNESCO World Heritage List. A variation of this limestone was historically, and until very few years ago, a primary building material in Malta. The temples are subject to various environmental influences which until recently have led to several collapses due in part to serious stone surface and infill loss. As a protection measure, open-sided shelters have been built over three of these temples. This work assesses the degrading influence of air pollution (nitrogen dioxide, ozone, particle matter, sulfur dioxide, and acidity in rain) on the temples, in combination and comparison with the influence of other environmental factors (relative humidity, temperature, precipitation, moisture, sea salt, wind) and in this respect evaluates the potential protective effect of the shelters. The variation in air pollution weathering of limestone exposed outdoor in Malta was calculated by exposure-response functions from the ICP-materials programme and compared with measured values, and its contribution to the deterioration of the temples was evaluated. The difference between urban and rural locations in Malta, in the first year of atmospheric chemical weathering of limestone due to air pollution, was found to be about one micrometer loss of stone surface. This is probably less than the annual variations due to the influence of natural climatic factors, and small compared to the present annual variations in continental Europe. The deposition of sea salt and presence of salts on and in the limestone megaliths and changes in salt-crystallization events due to relative humidity fluctuations, inside and outside the shelters, will account for more of the variations in the first year of weathering of Globigerina limestone than variations in air pollution. The deterioration will also be related to temperature (including condensation events), wind parameters and rainfall, as well as ground water replenished from areas beyond the shelter.
The use of inhibition chemicals holds the prospect of an efficient strategy to control crystalliz... more The use of inhibition chemicals holds the prospect of an efficient strategy to control crystallization in porous materials, thereby potentially contributing to the prevention or mitigation of the salt decay phenomenon in modern as well as historical building materials in a more sustainable manner. In this review, we first provide an essential background on the mechanism of salt crystallization and on the factors influencing this phenomenon; next, we illustrate the mechanism at the basis of the action of crystal growth inhibitors, and critically discuss the major advances in the development of different families of inhibitors, particularly focusing on their influence on salt transport and crystallization within the structure of porous media. Specifically, correlations between the crystallization inhibition processes in porous materials and variables, such as porous substrate composition and properties, contaminant salt type and concentrations, microclimatic conditions, inhibiting solution concentration and properties, and application methods, will be highlighted. Environmental aspects, limitations, and problems associated with some inhibition chemicals are also taken into account. Finally, a survey and a discussion on the most representative experimental techniques and instrumentation available to assess qualitatively and quantitatively the inhibitor effectiveness, as well as recently developed modelling tools are given out.
Ing. Arch. Gennaro Tampone passed away in February 2018, after a lifetime dedicated to studies on... more Ing. Arch. Gennaro Tampone passed away in February 2018, after a lifetime dedicated to studies on historic structures, their technology and their conservation. Whereas his studies on the conservation of ancient wooden structures won him international acclaim, his decades-long research on the Prehistoric Megalithic Temples of the Maltese Islands is possibly less well known. But it is no less significant. Ing. Tampone led and inspired a multi-disciplinary team of researchers and students – when multi-disciplinarity was not yet considered vital in the field of architectural or archaeological conservation – working in the field, in archives and in laboratories, to elucidate the mode of construction of these unique UNESCO inscribed structures, with the ultimate aim of their conservation. His many publications on the subject, also seminal papers in the Bollettino Ingegneri, attest to his firm belief in the intrinsic value of surveying, documenting, photographing and recording before trying to conserve, and to understanding underlying technologies and conservation issues. He was also a firm believer in the importance of the dissemination of information and the essential role of teaching and imparting knowledge. His sterling contribution to a general awareness, also amongst the archaeological community, of the great importance of the Temples as architectural forms in their own right, and as part of a “network” of Mediterranean megalithic and similar constructions, the discovery of the sophistication of the mode of construction of these early structures, the direct relation between materials and mode of construction, and above all the significance and validity of the contemporary architectural “models” found within the Temples have all resulted in a legacy which will not be forgotten.
The main building stone in the Maltese Islands is the Globigerina Limestone, of which the Lower m... more The main building stone in the Maltese Islands is the Globigerina Limestone, of which the Lower member is commonly used. This occurs in two types, the durable franka and the more easily weathered soil. Two types of fresh franka (bajda (white) and safra (yellow)), as well as fresh soli stone blocks, were obtained, based on the identification by quarry owners. Their designation was confirmed by geochemistry. Physical and mechanical properties of the three were investigated, including uniaxial compressive strength, water absorption by capillarity, permeability and porosimetry. Porosimetry results confirmed outcomes of previous research work. Soli was found to have a lower overall porosity, but a high percentage of small pores with practically no large pores. Some of the tested stones were then treated with a non-toxic phospho-organic compound containing carboxylic moieties as a salt inhibitor and the corresponding non-phosphorylated compound.
In book: in N.C. Vella, A.J. Frendo & H.C.R. Vella (eds), The Lure of the Antique. Essays on Malta and Mediterranean Archaeology in Honour of Anthony Bonanno, ISBN 978-90-429-3617-1.Publisher: Peeters Publishers, 2018
PREAMBLE In 1991, Prof. Anthony Bonanno and the current author wrote a paper entitled, “The deter... more PREAMBLE In 1991, Prof. Anthony Bonanno and the current author wrote a paper entitled, “The deterioration of cultural property by airborne pollutants: A case study of a Mediterranean Island”.1 This paper was presented at the European University Centre for Cultural Heritage, Ravello, Italy, as part of the Round Table on Airborne Particles: Their Negative Effects on the Cultural Heritage and its Environment. In the twenty-first century, earlier concerns on air pollution effects on cultural heritage have widened to encompass the effects of global climate change on cultural heritage. “Climate Change and Cultural Heritage” was the theme of a number of doctoral courses held in the Ravello Centre between 2009 and 2013. Within this series of courses, in 2013 the present author was invited to give a lecture on adaptation strategies for archaeological sites in connection with climate change. The current paper, which celebrates Prof. Bonanno’s lifetime academic achievements, is based on the contextual information gathered in preparation for that lecture, and includes the expected effects on a local case study, the Megalithic Temples of Malta. The paper on adaptation has been published by the Ravello European University Centre in a book entitled, Cultural Heritage from Pollution to Climate Change to Global Change.
Abstract: Numerous papers included within the broad subject of geomaterials have been published i... more Abstract: Numerous papers included within the broad subject of geomaterials have been published in QJEGH over the past 50 years. These have been compiled and divided here into three main categories: aggregates, building stone and earthworks. The aim of this review is to provide a comprehensive summary of the relevant papers published in QJEGH with a view to identifying the main areas of interest historically, now and in the future. Some clear trends are evident from the survey and review; for example, there has been a steady interest in building stone and in particular its deterioration, a decline in papers on earthworks and an increase in those on ground improvement (also covered here). It is also noted that methods of characterizing geomaterials are becoming more sophisticated with advancing technology. The review makes relevant links with other Special Publications from the Geological Society, including also Engineering Geology Special Publications.
Journal of Civil Engineering and Architecture 11 (2017) 175-183 , 2017
Ammonium oxalate treatment, previously extensively studied on limestone in the laborato... more Ammonium oxalate treatment, previously extensively studied on limestone in the laboratory, was applied to powdering historical stonework (limestone) situated on the shoreline in the Mediterranean Island of Malta. This paper presents the results obtained from onsite testing that aimed at evaluating the treatment in terms of its aesthetic performance, the depth of treatment, the mechanical properties of the consolidated stone and the influence on water transport. To this end, the testing program included colorimetry, DRMS (drilling resistance measurement system) and water absorption through the contact sponge method. This study is Part One of the final phase of a wider research program which included two previous phases progressing from treating this same very porous stone type in a laboratory-based controlled environment to uncontrolled site conditions, seeking to quantify this treatment’s effectiveness in the field. Results showed that onsite consolidation was achieved and that although some changes in colour and water absorption were brought about by the treatment, these were within acceptable tolerance limits. Besides carrying out these treatments and evaluations directly on the coast, this study anticipates further studies which will look at rural and urban sites where the types and concentrations of salts are expected to be different.
Bulletin of Engineering Geology and the Environment, 2015
The millenary use of Lower Globigerina Limestone (LGL) as the main building stone of the Maltese ... more The millenary use of Lower Globigerina Limestone (LGL) as the main building stone of the Maltese Islands is testimony to the importance of this resource to the local building industry. Today, the pressing need to conserve Malta’s rich patrimony of archaeological/historical masonry buildings and structures drives research in this field, particularly in view of the observed variable durability of this stone type. LGL has been described as a moderately weak calcarenite characterised by a predominance of calcite (86–99 %) and high porosity. In theory, these physical properties should make this type of stone particularly susceptible to deterioration involving (a) mechanisms of capillary salt-laden moisture accumulation and movement together with (b) thermodynamic changes in soluble salts during dissolution and crystallisation cycles. The study reported here forms part of a wider research programme aimed at characterising this resource. In this work, we assessed the durability of the LGL in a temperate Mediterranean climate characterised by two main factors, namely (i) a salt-laden marine environment and (ii) relatively short spans of heavy precipitation alternated with longer periods of virtual drought. The main aim of the study was to analyse macro/microporosity variations and minute, yet quantifiable, fluctuations in minor geochemical constituents of the stone with respect to observed weathering characteristics and accelerated crystallisation damage test results. This was achieved through systematic sampling and testing of retrieved core samples extracted from dimension-stone quarrying areas in Malta.
The purpose of this paper is to review the performance of the protective shelters installed over ... more The purpose of this paper is to review the performance of the protective shelters installed over three archaeological sites in Malta over the past decade, and to draw some key lessons learnt that may be useful to others when considering whether to adopt a similar solution. The conservation threats to the Megalithic Temples of Malta are introduced and defined—these range from material issues (loss of surface) to structural issues (cracking and dislodgement of stones leading to structural instability and collapses). Causes identified specifically included fluctuating environmental conditions: wetting and drying cycles and thermal fluctuations, combined with the salt-laden Mediterranean island environment. The recognition during the late twentieth century of these issues as key factors in the deterioration of these structures, and the strategy that was developed in response, are outlined. A key component of this strategy was the installation of protective shelters over three of the main megalithic sites. The process through which the design requirements for the shelters were defined is reviewed. The performance of the shelters is then examined, through a critical review of unpublished reports and published studies. An evidence-based summary of the beneficial effects of the shelters is provided, and the possibility of any harmful effects discussed. A number of lessons learnt through this process are then identified. One key lesson is that the microenvironment in a newly-sheltered site is at a transitional stage that does not necessarily reflect longer-term trends, which therefore require long-term monitoring to be understood. The choice and number of environmental parameters to be monitored need to be informed by a careful consideration of their sustainability, both in terms of equipment and human resources. Any monitoring programme, however well-designed, needs to be open to re-evaluation and revision where needed. As more experience and data are accumulated from different sheltering projects, it will become more feasible to establish performance indicators in advance of a sheltering intervention, on the basis of which to evaluate its performance. The experience of these projects is then used to inform a checklist of key considerations for anyone considering whether to shelter an archaeological site. The foremost consideration is that every site requires a site-specific strategy tailored to its needs. The decision whether a shelter is desirable, and what its performance requirements should be, may only be taken in the context of such a strategy. This paper should help define the parameters for such a decision to take place.
The Maltese Megalithic Temples, constructed between the mid-fourth and mid-third millennia BC, ar... more The Maltese Megalithic Temples, constructed between the mid-fourth and mid-third millennia BC, are unique and are amongst the oldest stone buildings of such complexity in the world. They are of great local and international significance, embodying symbolic, educational and recreational values. These Temples are currently suffering from a series of severe problems associated with the deterioration of materials as well as structural problems, seen in a number of serious collapses in recent years. In 2000, it was decided that these vulnerable prehistoric structures needed to be protected from the direct impact of environmental factors by means of a temporary, open-sided shelter, conceived as a large parasol designed to be as light as possible, in visual as well as in physical terms. The erection of two of these shelters took place during 2008–2009. The performance of the shelters is currently being assessed by environmental monitoring which already indicates an improvement in conditions beneath the shelters when compared to conditions on site before sheltering.
The Lower Globigerina Limestone of the Maltese Islands is here being proposed for nomination as a... more The Lower Globigerina Limestone of the Maltese Islands is here being proposed for nomination as a “Global Heritage Stone Resource”. This stone, continuously used for building and sculpture for 6000 years, is well suited to fit this global designation as it is not only of great local cultural, historic and economic importance, but it is also the building stone used in construction of the UNESCO, and hence internationally recognized, World Heritage city of Valletta, as well as the UNESCO-listed Prehistoric Megalithic Temples of the Maltese Islands. The stone was also exported to several European and North African countries especially in the early 20th century. The entire range of archaeological remains and historic architecture which cover the Maltese Islands have been built in this stone, and encompass innumerable palaces and churches, including the fortified cities of Valletta, Mdina (the old capital of Malta), the Three Cities on the Grand Harbour and the Citadel of Gozo, as well as the vernacular architecture ubiquitous within the village cores all over the Islands. The soft limestone has also been widely used over the millennia for elaborate and extensive sculptural motifs. Practically the only natural resource of the Islands, it continues to be quarried today, and is used not only for new construction, but also for the regular restoration of Malta’s great and imposing architectural heritage, remaining thus an important pillar of the Maltese economy.
Two of the seven prehistoric megalithic Temples of the Maltese Islands inscribed on the UNESCO Wo... more Two of the seven prehistoric megalithic Temples of the Maltese Islands inscribed on the UNESCO World Heritage List were covered by a temporary open-sided shelter in 2009. This was to protect the Temples from environmental factors, primarily direct rainfall and insolation, which were considered as primary causes of deterioration of both the materials and the structures. The sheltering was preceded by an intense environmental monitoring campaign which lasted for one year, and which was then partially continued even after the sheltering. This paper, which evaluates the changes in environmental conditions both before and after sheltering, concludes that the advantages of the shelter far outweigh the disadvantages. Caution is however advocated in the case of noted disadvantages, such as salt, dust and pollution accumulation on the now protected megaliths, which should continue to be carefully monitored for any possible deleterious effects. Recommendations are also given for maintenance actions which can prevent these events from negatively affecting the state of conservation of the megaliths. These include the dry, soft regular brushing of the megaliths, and the surrounding ground, to remove accumulated salts which can cause the limestone to deteriorate if reabsorbed back into the porous stone on occasions when condensation events, which have been detected during the monitoring campaign even after the sheltering, occur.
Climate change varies from temperature increases, to changes in humidity cycles, to increased fr... more Climate change varies from temperature increases, to changes in humidity cycles, to increased frequency and severity of extreme events. The known and predicted effects of this change on the archaeological heritage, both that which is known and that which is still buried, will be summarised in this paper. A synopsis of the main reports and recommendations by UNESCO and ICOMOS, the two main international players where the safeguarding of heritage properties are concerned, will be given, with special emphasis on how these affect archaeological sites, and how these measures can actually be put into practice. Finally, current actions for the conservation of a World Heritage site may be affected by climate change – a case study – will be discussed.
Le changement climatique varie d'augmentation de la température, de changements dans les cycles d'humidité, à l'augmentation de la fréquence et de la gravité des événements extrêmes. Les effets connus et prévus de ce changement sur le patrimoine archéologique, à la fois ce qui est connu et ce qui est encore enfouis, seront résumés dans le présent document. Un résumé des principaux rapports et recommandations de l'UNESCO et de l'ICOMOS, les deux principaux acteurs internationaux où la sauvegarde des biens du patrimoine sont concernés, sera donnée, avec un accent particulier sur la façon dont celles–ci affectent les sites archéologiques, et comment ces mesures peuvent effectivement être mis en pratique. Enfin, les actions en cours pour la conservation d'un site du patrimoine mondial peuvent être affectés par le changement climatique – une étude de cas – seront discutés.
The International Commission on Geoheritage (ICG) of the International Union of Geological Scienc... more The International Commission on Geoheritage (ICG) of the International Union of Geological Sciences identifies, recognises, and designates significant geological heritage sites, stones, and collections (https://iugs-geoheritage.org/). The Subcommission on Heritage Stones designated 55 stones that has been used in significant architecture and monuments, recognized as integral aspects of human culture as IUGS Heritage Stones since 2016.
In this first-of-a-kind book, “The First 55 IUGS Heritage Stones”, we celebrate building stones, decorative stones and stones used for statuary, which embody human ingenuity and skill and are testimony to cultures and societies, which have appeared - and disappeared - over time. Stone has the ability to merge the tangible with the intangible and thus bears testimony to rituals, traditions, religion, ceremonies and human resilience, as well as past technologies, manual skills and even interconnectivity across space and time.
The main focus of this book is to clarify the current use of 200 terms within different cultures ... more The main focus of this book is to clarify the current use of 200 terms within different cultures and languages. The goal is to convey the essence and to be accurate, but not to be exhaustive. It addresses a widely diverse range of readers: professionals, to help them with their daily work, especially if their work extends to other European countries; administrative authorities, to give them a tool for communicating their tasks; conservation students in Europe, to provide them with common educational material; individuals, to aid them in understanding deterioration and preservation processes within their built environment.
(2013) Introduction to the stone cycle and the conservation of historic buildings. Quarterly Journal of Engineering Geology and Hydrogeology, 46 (4). pp. 363-366. ISSN 1470-9236 10.1144/qjegh2013-052
This thematic set of papers relating to the life cycle of building stone was initiated by a call ... more This thematic set of papers relating to the life cycle of building stone was initiated by a call for papers in order to better recognize the contribution that the disciplines, and practitioners, of engineering geology and hydrogeology make to the conservation of historical buildings, which is intrinsically multidisciplinary. The call for papers particularly focused upon the issues of different stone types used in historical buildings, as well as the performance, durability and conservation of stone in historical settings.
The very well attended seminar showcased this research to an audience which included scholars, ac... more The very well attended seminar showcased this research to an audience which included scholars, academics, students, Cultural Heritage professionals and interested individuals. This seminar also formed part of the celebrations of the 10 th anniversary of the establishment of Heritage Malta as the National Agency for museums, conservation practice and cultural heritage. As I had remarked when addressing the closing session of the conference, this was the brainchild of Heritage Malta's Research Programme SubCommittee which I chair and which was set up to enable and promote all possible aspects of research related to the sites, museums and collections under the care of Heritage Malta. The members of this subcommittee envisaged this conference as a vehicle for presenting, on as wide a scale as possible, this sterling work which is not usually much promoted at the local level. The high response generated was however not expected. Although we knew that much sound research was going on, we were extremely pleased to note that so many professional staff were willing to show, explain and discuss the scientific work which goes on quietly, but continuously, behind the scenes. This is a true reflection of some of the excellent work carried out by Heritage Malta's dedicated staff. The nine papers presented in this concise but significant volume ably mirror the previously mentioned wide range of research activities which are a fundamental part of Heritage Malta's work. They also provide a good insight into the research that goes on behind the walls of museums, archaeological sites, conservation studios and scientific laboratories, which is an essential part of Heritage Malta's commitment to the preservation of our past, and its presentation to the world at large, with its diverse and multiple audiences, and their varied desires and needs.
FOREWARD
As Chair of Heritage Malta’s Research Committee I feel honoured to have been asked to wr... more FOREWARD As Chair of Heritage Malta’s Research Committee I feel honoured to have been asked to write the Foreword to this first publication of a collection of research papers showcasing the breadth, and depth, of Heritage Malta’s research interests. These papers were presented during a public seminar held at the Aula Magna of the University of Malta Valletta Campus on 13 September 2013. The very well attended seminar showcased this research to an audience which included scholars, academics, students, Cultural Heritage professionals and interested individuals. This seminar also formed part of the celebrations of the 10th anniversary of the establishment of Heritage Malta as the National Agency for museums, conservation practice and cultural heritage.
As I had remarked when addressing the closing session of the conference, this was the brainchild of Heritage Malta’s Research Programme Sub-Committee which I chair and which was set up to enable and promote all possible aspects of research related to the sites, museums and collections under the care of Heritage Malta. The members of this sub-committee envisaged this conference as a vehicle for presenting on as wide a scale as possible this sterling work which is not usually much promoted at the local level. The high response generated was however not expected. Although we knew that much sound research was going on, we were extremely pleased to note that so many professional staff were willing to show, explain and discuss the scientific work which goes on quietly but continuously behind the scenes. This is a true reflection of some of the excellent work carried out by Heritage Malta’s dedicated staff.
The nine papers presented in this concise but significant volume ably mirror the previously mentioned wide range of research activities which are a fundamental part of Heritage Malta’s work. They also provide a good insight into the research that goes on behind the walls of museums, archaeological sites, conservation studios and scientific laboratories, which is an essential part of Heritage Malta’s commitment to the preservation of our past, and its presentation to the world at large, with its diverse and multiple audiences, and their varied desires and needs. ............
It can be concluded that the papers, though at first glance widely different, also have several common threads. They are certainly a window onto the varied and excellent research being carried out across the various Heritage Malta sections and museums, and it is hoped that they will serve as a stimulus to aspiring cultural heritage professionals to develop an interest in these field. They are however also a vivid illustration of the intricate interdisciplinarity which forms the foundation of modern-day conservation and of the importance of ethics and values when preserving and presenting cultural heritage artifacts and sites. These go hand-in-hand with time and patience, as well as discipline, training and research building towards what is today widely considered an important educational and informative area - presenting cultural heritage to the world at large, and preserving it for present and future generations.
I sincerely hope that this compendium of research papers will be read with the same interest and enthusiasm shown by the audience during the conference, and that I myself experienced when helping to edit this book. I conclude by auguring that Heritage Malta will continue to support the sterling research activities of its professional staff, which I hope will also be disseminated in a follow-up volume in the not-so-distant future.
Professor JoAnn Cassar Chair Heritage Malta Research Programme Sub-Committee
EwaGlos, which has been developed in eleven languages, highlights the crucial role that professio... more EwaGlos, which has been developed in eleven languages, highlights the crucial role that professionally developed multilingual vocabularies play in international preservation campaigns. The illustrated glossary stresses the importance of a common language in the conservation field, and the role that international cooperation plays in creating this common terminology. The core of the glossary comprises approximately 200 definitions of terms frequently used in specifications in the field of conservation-restoration of wall paintings and architectural surfaces. The forewords and preface of the book introduce professionals, students and decision-makers to complex issues encountered in the development, and use, of such terminologies. The book concludes with an extensive bibliography in this specialised field.
Transcending Boundaries: Integrated Approaches to Conservation. ICOM-CC 19th Triennial Conference Preprints, Beijing, 17–21 May 2021, ed. J. Bridgland. Paris: International Council of Museums., 2021
Heritage science requires a combination of knowledge from a large number of diverse disciplines, ... more Heritage science requires a combination of knowledge from a large number of diverse disciplines, transcending boundaries in a way that is often difficult, or even impossible, to achieve by individuals or small research groups. This paper reports on the latest developments in the advancement of a shared global research infrastructure representing an advanced research community that has been systematically developing since 1999, providing access to analytical facilities, research and networking. Most users of this network have been involved in scientific research. This current initiative is reaching out to all heritage sectors to ensure that the research being carried out is appropriate, necessary, relevant and accessible to all heritage professionals. This paper is a first step in this outreach to the conservation community in its widest sense. Our goal is to set up a dialogue in which common aims are identified and common solutions sought, to benefit all branches of heritage science.
Since their excavation, a number of the sites listed as part of "The Megalithic Temples of Malta"... more Since their excavation, a number of the sites listed as part of "The Megalithic Temples of Malta" inscription on the UNESCO World Heritage list have been afflicted by material and structural problems, including collapses. Therefore, three of these sites, the Ħaġar Qim, Mnajdra and Tarxien Temples, were protected by open-sided shelters, to address some of the principal causes of deterioration (e.g. direct rainfall, surface weathering, thermal stress). Environmental monitoring, condition assessments and biological surveys of the three sites took place before and after sheltering and are still in progress. To understand how the shelters are affecting these structures, a research programme has started aimed at analysing, through Computational Fluid Dynamics (CFD), the environmental data collected over a period of more than ten years. The aim of using CFD on the Temples is to provide detailed information on how different environmental conditions can affect the sites. For the CFD, macro and meso scale approaches will be used. The macroscale model represents the regional environment, including the all-terrain features around the Temples. Mesoscale modelling represents the Temple structures in a more detailed way. The final goal is to find confident correlations between CFD, and representative areas selected within the Temples showing particular deterioration patterns. All this information will be integrated with the results of in situ analyses to identify the causes of material deterioration and possibly mitigate against them.
Introduction
A carbonate rock, by definition, consists of more than 50% of carbonate minerals, ... more Introduction A carbonate rock, by definition, consists of more than 50% of carbonate minerals, calcite and/or dolomite. Within this category fall the limestones, marble and dolostones which have for thousands of years been used for construction and decorative purposes. This is because of their availability, ease of working, beauty, ability to take a polish, and/or durability. When mentioning these materials, the prehistoric (limestone) Temples of Malta, the (marble) Acropolis of Athens, the wide-ranging exploitation, exportation and use of coloured marbles by the Romans, the David (marble) by Michaleangelo, and countless other prestigious monuments, sites and statuary come to mind. Today, these materials remain important contributors to the economy, not least of all through tourism, and the construction industry.
Conference: 16th Euroseminar on Microscopy Applied to Building MaterialsAt: Les Diablerets, Switzerland, 2017
This paper focuses on the crystal structure orientation of calcium oxalate when formed on histori... more This paper focuses on the crystal structure orientation of calcium oxalate when formed on historical limestone on site, in the presence of mixed types of naturally occurring soluble salts. Examination of Maltese Globigerina Limestone (GL) samples, treated with the precursor material ammonium oxalate revealed different orientations of calcium oxalate crystals under Scanning Electron Microscopy (SEM). Crystal orientation was seen to be directly related to salt conditions during treatment. Site conditions generally include marine and industrially polluted environments where both soluble salts and water are present. As a first step towards evaluating the treatment within this context, and prior to site investigations, laboratory samples were contaminated with saturated solutions of known soluble salts prior to ammonium oxalate treatment. These salts included sodium chloride, sodium sulfate and sodium nitrate, applied separately. Electron micrographs of GL samples treated in the presence of soluble salts were examined and directly compared to GL samples treated in a salt-free environment. Results showed that calcium oxalate crystals formed in layers, parallel to the general direction of the calcite surface in the desalinated stone. In contrast, when treatment was effected in the presence of concentrated soluble salts, in all cases, the calcium oxalate crystals deposited perpendicularly to the general direction of the calcite surface. These differences were attributed, in part, to the physical obstructions caused by the salt crystals which induce calcium oxalate crystals to form around them, while in the absence of the former, the calcium oxalate can deposit parallel to the general direction of the stone. Continued research is ongoing.
Conference: International Symposium Consolidation & Communication Materials and Methods for the Consolidation of Cultural Heritage: An Interdisciplinary DialogueAt: Hildesheim, Germany, 2018
The consolidation of a soft porous limestone, often heavily contaminated with soluble salts, and ... more The consolidation of a soft porous limestone, often heavily contaminated with soluble salts, and generally found making up the architectural and archaeological fabric in the Mediterranean, is being discussed here, in particular ammonium oxalate treatment. This treatment was chosen following positive results published in the literature and extended local research. The lack of suitable consolidating treatments for porous stone in such environments, as well as possible interactions of the proposed treatment with the naturally occurring soluble salts on site, initiated this research programme. The long-term study, which was structured into three independent but interrelated phases, aimed at investigating such possible interactions, one variable at a time, in the laboratory, and led to an understanding of the complex interactions on site. Soft and porous limestone is particularly susceptible to salt deterioration; one typical example of this is the Maltese Globigerina Limestone, a highly porous limestone which is representative of others present in the Mediterranean (other similar examples include Pietra di Lecce and Pietra di Noto). This limestone from Malta was used throughout this research. Three soluble salt types were identified as being the most representative of a Mediterranean scenario, these being chlorides, sulfates and nitrates. In Phase 1, previously desalinated quarry samples were artificially contaminated with individual chloride, sulfate and nitrate salts of sodium, treated with ammonium oxalate and tested, under controlled laboratory conditions. This study then progressed to Phase 2, where a parallel set of salt-contaminated samples, identical to those studied in Phase 1, were introduced to external inland, urban conditions, treated on site, allowed to weather naturally for 1 year and then similarly tested in situ. In the third and final phase, naturally weathered stone on a wall in the same urban environment, forming part of a historical building, was characterized, treated and tested on site. In all cases, treatment was applied using a 5% ammonium oxalate monohydrate poultice, as established in the early 1980s. The testing, on untreated and treated stone, was designed to evaluate aesthetic changes through colorimetry, depths of calcium oxalate formation and physical properties of newly formed calcium oxalate through Drilling Resistance Measurement System (DRMS) and the tape test as well as the water transport properties through the contact sponge method. Treatment resulted in an aesthetic improvement, surface consolidation was verified, while adequate water transport properties in the liquid phase were retained. The depth of whewellite formed, which ranged from 0.7 mm to 1.6 mm, was found to be related to the presence of soluble salts during treatment. Results were considered to be very positive and also brought out further areas of research that merit investigation for the continued development of in situ conservation of salt-contaminated porous limestone, which could be applicable to similar stones in the Mediterranean. This will however need to be preceded by even further research, especially in situ.
Presented at Conference at end of European Project Nano-Cathedral: Nanomaterials for Conservation... more Presented at Conference at end of European Project Nano-Cathedral: Nanomaterials for Conservation of European Architectural Heritage, 2018 (Pisa, Italy)
This paper focuses on the effects of natural weathering on Globigerina Limestone (Malta) which wa... more This paper focuses on the effects of natural weathering on Globigerina Limestone (Malta) which was treated with ammonium oxalate to produce a calcium oxalate surface layer. This study includes the first two phases of a larger research programme. Laboratory samples were considered first. These were treated and tested in a controlled environment (Phase 1). Identical samples sets were prepared for Phase 2. These were treated in situ and exposed to site conditions for the period of one year. In an attempt to simulate site conditions, for both Phase 1 and Phase 2 samples, the limestone was contaminated with soluble salts before treatment took place. These included three separate types; sodium chloride, sodium sulfate and sodium nitrate. Desalinated samples were also included in the study. Scanning Electron Microscopy (SEM) was carried out on the Phase 1 samples while Drilling Resistance Measurement System (DRMS) was carried out on the samples of both phases. This paper focuses on the results from the SEM and correlates these with those results from the DRMS in light of the influence of natural weathering on an artificial calcium oxalate layer, induced in the presence of soluble salts.
SCIENCE AND ART: A FUTURE FOR STONE PROCEEDINGS OF THE 13TH INTERNATIONAL CONGRESS ON THE DETERIORATION AND CONSERVATION OF STONE 6th to 10th September 2016, Paisley, ScotlandVolume: Volume 1, 2016
Surface consolidation treatments on stone materials induce relevant modifications in the porous s... more Surface consolidation treatments on stone materials induce relevant modifications in the porous substrates that can potentially trigger deterioration phenomena not active in the same untreated materials. Unlike most protective products that form films on stone surfaces, consolidants must penetrate the first layers of the substrate in order to function, partially filling the voids of the porous network. Meso- and macro-porosities of Globigerina Limestone (Malta’s highly porous sedimentary stone), before and after treatments with several organic and inorganic consolidants were investigated by means of N2-BET (Brunauer–Emmett–Teller) analysis. BET total inner superficial area together with pore size distribution data gave interesting information on preferential distribution of different products inside the open porosity network. The treatment can produce in some cases small changes in total superficial area (inorganic treatment), in some others cases a dramatic reduction (organic) and also an unexpected relevant increase (ethylsilicate). Pore size distribution shows shifts towards lower pore diameters turning a predominantly macroporous system into a meso-porous one. These porosimetric changes have a direct relationship with the physical properties of porous building materials. In relation to the environmental context and the direct exposure to deterioration agents, the consolidation treatment can also have a negative impact for the conservation of works of art.
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Papers by JoAnn Cassar
sustainable manner. In this review, we first provide an essential background on the mechanism of salt crystallization and on the factors influencing this phenomenon; next, we illustrate the mechanism at the basis of the action of crystal growth inhibitors, and critically discuss the major advances in the development of different families of inhibitors, particularly focusing on their influence on salt transport and crystallization within the structure of porous media. Specifically,
correlations between the crystallization inhibition processes in porous materials and variables, such as porous substrate composition and properties, contaminant salt type and concentrations, microclimatic conditions, inhibiting solution concentration and properties, and application methods, will be highlighted. Environmental aspects, limitations, and problems associated with some inhibition chemicals are also taken into account. Finally, a survey and a discussion on the most
representative experimental techniques and instrumentation available to assess qualitatively and quantitatively the inhibitor effectiveness, as well as recently developed modelling tools are given out.
past 50 years. These have been compiled and divided here into three main categories: aggregates, building stone and
earthworks. The aim of this review is to provide a comprehensive summary of the relevant papers published in QJEGH
with a view to identifying the main areas of interest historically, now and in the future. Some clear trends are evident from
the survey and review; for example, there has been a steady interest in building stone and in particular its deterioration, a
decline in papers on earthworks and an increase in those on ground improvement (also covered here). It is also noted that
methods of characterizing geomaterials are becoming more sophisticated with advancing technology. The review makes
relevant links with other Special Publications from the Geological Society, including also Engineering Geology Special
Publications.
Le changement climatique varie d'augmentation de la température, de changements dans les cycles d'humidité, à l'augmentation de la fréquence et de la gravité des événements extrêmes. Les effets connus et prévus de ce changement sur le patrimoine archéologique, à la fois ce qui est connu et ce qui est encore enfouis, seront résumés dans le présent document. Un résumé des principaux rapports et recommandations de l'UNESCO et de l'ICOMOS, les deux principaux acteurs internationaux où la sauvegarde des biens du patrimoine sont concernés, sera donnée, avec un accent particulier sur la façon dont celles–ci affectent les sites archéologiques, et comment ces mesures peuvent effectivement être mis en pratique. Enfin, les actions en cours pour la conservation d'un site du patrimoine mondial peuvent être affectés par le changement climatique – une étude de cas – seront discutés.
sustainable manner. In this review, we first provide an essential background on the mechanism of salt crystallization and on the factors influencing this phenomenon; next, we illustrate the mechanism at the basis of the action of crystal growth inhibitors, and critically discuss the major advances in the development of different families of inhibitors, particularly focusing on their influence on salt transport and crystallization within the structure of porous media. Specifically,
correlations between the crystallization inhibition processes in porous materials and variables, such as porous substrate composition and properties, contaminant salt type and concentrations, microclimatic conditions, inhibiting solution concentration and properties, and application methods, will be highlighted. Environmental aspects, limitations, and problems associated with some inhibition chemicals are also taken into account. Finally, a survey and a discussion on the most
representative experimental techniques and instrumentation available to assess qualitatively and quantitatively the inhibitor effectiveness, as well as recently developed modelling tools are given out.
past 50 years. These have been compiled and divided here into three main categories: aggregates, building stone and
earthworks. The aim of this review is to provide a comprehensive summary of the relevant papers published in QJEGH
with a view to identifying the main areas of interest historically, now and in the future. Some clear trends are evident from
the survey and review; for example, there has been a steady interest in building stone and in particular its deterioration, a
decline in papers on earthworks and an increase in those on ground improvement (also covered here). It is also noted that
methods of characterizing geomaterials are becoming more sophisticated with advancing technology. The review makes
relevant links with other Special Publications from the Geological Society, including also Engineering Geology Special
Publications.
Le changement climatique varie d'augmentation de la température, de changements dans les cycles d'humidité, à l'augmentation de la fréquence et de la gravité des événements extrêmes. Les effets connus et prévus de ce changement sur le patrimoine archéologique, à la fois ce qui est connu et ce qui est encore enfouis, seront résumés dans le présent document. Un résumé des principaux rapports et recommandations de l'UNESCO et de l'ICOMOS, les deux principaux acteurs internationaux où la sauvegarde des biens du patrimoine sont concernés, sera donnée, avec un accent particulier sur la façon dont celles–ci affectent les sites archéologiques, et comment ces mesures peuvent effectivement être mis en pratique. Enfin, les actions en cours pour la conservation d'un site du patrimoine mondial peuvent être affectés par le changement climatique – une étude de cas – seront discutés.
In this first-of-a-kind book, “The First 55 IUGS Heritage Stones”, we celebrate building stones, decorative stones and stones used for statuary, which embody human ingenuity and skill and are testimony to cultures and societies, which have appeared - and disappeared - over time. Stone has the ability to merge the tangible with the intangible and thus bears testimony to rituals, traditions, religion, ceremonies and human resilience, as well as past technologies, manual skills and even interconnectivity across space and time.
As Chair of Heritage Malta’s Research Committee I feel honoured to have been asked to write the Foreword to this first publication of a collection of research papers showcasing the breadth, and depth, of Heritage Malta’s research interests. These papers were presented during a public seminar held at the Aula Magna of the University of Malta Valletta Campus on 13 September 2013. The very well attended seminar showcased this research to an audience which included scholars, academics, students, Cultural Heritage professionals and interested individuals. This seminar also formed part of the celebrations of the 10th anniversary of the establishment of Heritage Malta as the National Agency for museums, conservation practice and cultural heritage.
As I had remarked when addressing the closing session of the conference, this was the brainchild of Heritage Malta’s Research Programme Sub-Committee which I chair and which was set up to enable and promote all possible aspects of research related to the sites, museums and collections under the care of Heritage Malta. The members of this sub-committee envisaged this conference as a vehicle for presenting on as wide a scale as possible this sterling work which is not usually much promoted at the local level. The high response generated was however not expected. Although we knew that much sound research was going on, we were extremely pleased to note that so many professional staff were willing to show, explain and discuss the scientific work which goes on quietly but continuously behind the scenes. This is a true reflection of some of the excellent work carried out by Heritage Malta’s dedicated staff.
The nine papers presented in this concise but significant volume ably mirror the previously mentioned wide range of research activities which are a fundamental part of Heritage Malta’s work. They also provide a good insight into the research that goes on behind the walls of museums, archaeological sites, conservation studios and scientific laboratories, which is an essential part of Heritage Malta’s commitment to the preservation of our past, and its presentation to the world at large, with its diverse and multiple audiences, and their varied desires and needs.
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It can be concluded that the papers, though at first glance widely different, also have several common threads. They are certainly a window onto the varied and excellent research being carried out across the various Heritage Malta sections and museums, and it is hoped that they will serve as a stimulus to aspiring cultural heritage professionals to develop an interest in these field. They are however also a vivid illustration of the intricate interdisciplinarity which forms the foundation of modern-day conservation and of the importance of ethics and values when preserving and presenting cultural heritage artifacts and sites. These go hand-in-hand with time and patience, as well as discipline, training and research building towards what is today widely considered an important educational and informative area - presenting cultural heritage to the world at large, and preserving it for present and future generations.
I sincerely hope that this compendium of research papers will be read with the same interest and enthusiasm shown by the audience during the conference, and that I myself experienced when helping to edit this book. I conclude by auguring that Heritage Malta will continue to support the sterling research activities of its professional staff, which I hope will also be disseminated in a follow-up volume in the not-so-distant future.
Professor JoAnn Cassar
Chair
Heritage Malta
Research Programme Sub-Committee
February 2016
The core of the glossary comprises approximately 200 definitions of terms frequently used in specifications in the field of conservation-restoration of wall paintings and architectural surfaces. The forewords and preface of the book introduce professionals, students and decision-makers to complex issues encountered in the development, and use, of such terminologies. The book concludes with an extensive bibliography in this specialised field.
is often difficult, or even impossible, to achieve by individuals or small research groups. This paper reports on the latest developments in the
advancement of a shared global research infrastructure representing an advanced research community that has been systematically developing
since 1999, providing access to analytical facilities, research and networking. Most users of this network have been involved in scientific
research. This current initiative is reaching out to all heritage sectors to ensure that the research being carried out is appropriate, necessary,
relevant and accessible to all heritage professionals. This paper is a first step in this outreach to the conservation community in its widest sense. Our goal is to set up a dialogue in which common aims are identified and common solutions sought, to benefit all branches of heritage science.
A carbonate rock, by definition, consists of more than 50% of carbonate minerals, calcite and/or dolomite. Within this category fall the limestones, marble and dolostones which have for thousands of years been used for construction and decorative purposes. This is because of their availability, ease of working, beauty, ability to take a polish, and/or durability. When mentioning these materials, the prehistoric (limestone) Temples of Malta, the (marble) Acropolis of Athens, the wide-ranging exploitation, exportation and use of coloured marbles by the Romans, the David (marble) by Michaleangelo, and countless other prestigious monuments, sites and statuary come to mind. Today, these materials remain important contributors to the economy, not least of all through tourism, and the construction industry.
were considered first. These were treated and tested in a controlled environment (Phase 1). Identical samples sets were prepared for Phase 2. These were treated in situ and exposed to site conditions for the period of one year. In an attempt to simulate site conditions, for both
Phase 1 and Phase 2 samples, the limestone was contaminated with soluble salts before treatment took place. These included three separate types; sodium chloride, sodium sulfate and sodium nitrate. Desalinated samples were also included in the study. Scanning Electron
Microscopy (SEM) was carried out on the Phase 1 samples while Drilling Resistance Measurement System (DRMS) was carried out on the samples of both phases. This paper focuses on the results from the SEM and correlates these with those results from the DRMS in light of the influence of natural weathering on an artificial calcium oxalate layer, induced in the presence of soluble salts.
environmental context and the direct exposure to deterioration agents, the consolidation treatment can also have a negative impact for the conservation of works of art.