Mortars from the palace of Knossos in Crete, Greece: A multi-analytical approach

The study of building materials constituting cultural heritage is fundamental to understand their characteristics and predict their behavior. When considering materials from archaeological sites, their characterization can provide not only relevant information for a broader understanding of the site and its importance and significance but can also increase knowledge about ancient materials and their performance. The Palace of Knossos is a very important archaeological site in the European history context, and its preservation benefits from the characterization of the constituent materials. Samples of mortars from this monument were collected under the scope of the H2020 HERACLES project, where a multi-analytical approach was chosen using established protocols for the different sample typologies. Instrumental techniques such as optical microscopy (OM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and simultaneous thermogravimetry and differential thermal analysis (TG–DTA) were used for the chemical, mineralogical, and morphological characterization of these mortar samples. The results indicate that the majority are lime mortars, both aerial and hydraulic, but gypsum-based mortars were also identified. Differences in the chemical composition of the samples in distinct areas of the monument allowed us to reflect on the variety of materials used in the construction of the Palace of Knossos.publishersversionpublishe

The Palace of Knossos Case Study and Material Characterization

The funding from the European Union Horizon 2020 research and innovation programme H2020-DRS-2015 GA nr. 700395 (HERACLES project).The study and characterization of mortars is generally related to the knowledge of the properties of the material, which guarantee or improve its performance and durability. When we consider the study of historical mortars, the main objective is to understand the characteristics of the material and how it has reached the present day, considering that, often, the time of its preparation and application is separated from the present by a long period of time, perhaps centuries, and is thus difficult to specify. This type of study may give indications on historical issues relevant to the understanding of a particular site or monument and, in addition, can assist in actions related to its preservation. Mortars can be used with different functions, ranging from structural function, protection, or finish, which requires distinct properties that are suitable for this functionality. It is necessary to consider that the desired characteristics, after drying the mortar, will depend on a set of factors, including the selection and quality of the raw material, the proportion between the main components, the way they are prepared and applied, and the environmental conditions they will be subjected to over time. Furthermore, the larger the monument is, the greater the chances of changes, reconstructions or interventions, including materials prepared in different periods with different raw materials and techniques. This is precisely the case of the Palace of Knossos, located near the Heraklion in Crete. It is estimated that the first palace was built in 2000 B.C.; however, it was destroyed and rebuilt more majestically in 1700 B.C. The definitive abandonment of the palace would have occurred around 1450 B.C., but the site where it was built maintained its importance for many centuries. Excavated at the beginning of the 20th century, the Palace of Knossos is one of the most important archaeological sites in Europe, both for its size and the complexity of its plant, with architectural solutions worthy of a well-developed civilization, as well as for the many reclaimed materials and frescos found. In addition to all of the material wealth found in its excavation, the palace has undergone peculiar historical conservation including the reconstruction of many of its structures, even as late as the early 20th century, all considered of great importance for the history of the monument. For this study, samples of mortars were collected at different points of the Palace of Knossos, both from areas of archaeological remains as well as from reconstructed areas. For the characterization, we opted for a multi-analyses approach which involved optical microscopy observation, X-ray fluorescence, X-ray diffraction, FTIR, -Raman, simultaneous thermogravimetry and differential thermal analysis. The results obtained indicated that the samples were mostly lime mortars with different hydraulicity indexes produced from local raw materials. The results also indicated that the samples presented considerable differences depending on the area in which they were collected, showing the variety and complexity of the materials produced in different periods, even when used for the same function.publishersversionpublishe

Spectroscopic and Morphological Studies of Metal-Organic and Metal-Free Dyes onto Titania Films for Dye-Sensitized Solar Cells

We have investigated the spectroscopic behavior of three different sensitizers adsorbed onto titania thin films in order to gain information both on the electron transfer process from dye to titania and on the anchorage of the chromophore onto the semiconductor. We have examined by UV-Vis and fluorescence spectroscopy the widely used ruthenium complex cis-di(thiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)ruthenium(II) (N719), the more recently developed organic molecular 3-(5-(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D5), and a push-pull zinc phthalocyanine sensitizer (ZnPc). Three type of titania films with different morphology, characterized by SEM and FT-IR measurement, were considered: a mesoporous transparent film deposited by spin-coating (TiMS), a semiopaque film deposited by doctor-blade from mesoporous titania (TiMS_DB) and a semiopaque film deposited by doctor-blade form commercial P25 titania (P25_DB). The use of TiMS is responsible for the adsorption of a higher amount of dye since the mesoporous structure allows increasing the interfacial area between dye and titania. Moreover, the fluorescence emission peak is weaker when the sensitizers are adsorbed onto TiMS. These findings suggest that mesostructured films could be considered the most promising substrates to realize photoanodes with a fast electron transfer process

Structural Assessment via Ground Penetrating Radar at the Consoli Palace of Gubbio (Italy)

Ground Penetrating Radar (GPR) is a flexible and cost-effective tool for performing structural integrity assessment and quick damage evaluation of manmade structures, including cultural heritage (CH) assets. In this context, this paper deals with the usefulness of GPR surveys enhanced by the use of a Microwave Tomographic data processing approach as a methodology for the diagnosis and monitoring of CH exposed to climate events and natural hazards. Specifically, the paper reports on the results of a measurement campaign carried out at the Loggia of the Consoli Palace of Gubbio (Italy). These results allowed us to increase our knowledge of the architecture of the surveyed zones and their structural hazards

HERACLES: EU-backed multinational project on cultural heritage preservation

In 2016, the European Unions’ Research and Innovation program Horizon 2020 launched the multi-national project called HEritage Resiliance Against CLimatic Events on Site (HERACLES). The goal of this project is to design, validate and promote effective and sustainable solutions against potential threats climatic changes can bring about on the cultural heritage. For this purpose, knowledge and experiences of multiple research facilities and versatile groups of end-users in different European countries will be bundled and synergetically benefited of. In this paper, we will provide an overview about HERACLES project while a particular focus will be put on the activities concerning close-range Remote Sensing data processing. By exploiting image and laser data acquired from UAVs and from the ground, we strive for precise and reliable 3D models that are useful for representation of the scene on the desired level of detail and thus for assessing potential damages and estimating risks. From oblique UAV-borne imagery, we will obtain textured airborne 3D models using photogrammetric methods of image alignment, dense point cloud reconstruction, meshing and texturing. To provide coverage for the objects’ interiors, very dense point clouds from terrestrial laser scans can be additionally captured. A triangle mesh is obtained from these points and textured by means of terrestrial high-resolution photos, whereby the registration took place using a point-based method. We identified two main challenges: first, the reconstruction results from high-resolution UAV images were not always satisfying due to a low coverage; to cope with this, extensive interactive corrections must be undertaken. Moreover, seamless merging of triangle meshes provided by aerial photogrammetric reconstruction and by terrestrial laser scans is cumbersome because of varying density and accuracy of 3D points in both meshes

Ancient Mercury-Based Plating Methods: Combined Use of Surface Analytical Techniques for the Study of Manufacturing Process and Degradation Phenomena

Fire gilding and silvering are age-old mercury-based processes used to coat the surface of less precious substrates with thin layers of gold or silver. In ancient times, these methods were used to produce and decorate different types of artefacts, such as jewels, statues, amulets, and commonly-used objects. Gliders performed these processes not only to decorate objects but also to simulate the appearance of gold or silver, sometimes fraudulently. From a technological point of view, the aim of these workmen over 2000 years ago was to make the precious metal coatings as thin and adherent as possible. This was in order to save expensive metals and to improve the resistance to the wear caused by continued use and circulation. Without knowledge about the chemical-physical processes, the ancient craftsmen systematically manipulated these metals to create functional and decorative artistic objects. The mercury-based methods were also fraudulently used in ancient times to produce objects such as jewels and coins that looked like they were made of silver or gold but actually had a less precious core. These coins were minted by counterfeiters but also by the official issuing authorities. The latter was probably because of a lack of precious metals, reflecting periods of severe economic conditions. In this Account, we discuss some representative cases of gold- and silver-coated objects, focusing on unique and valuable Roman and Dark Ages period works of art, such as the St. Ambrogio's altar (825 AD), and commonly used objects. We carried out the investigations using surface analytical methods, such as selected area X-ray photoelectron spectroscopy and scanning electron microscopy combined with energy-dispersive spectroscopy. We used these methods to investigate the surface and subsurface chemical features of these important examples of art and technology, interpreting some aspects of the manufacturing methods and of disclosing degradation agents and mechanisms. These findings may contribute to cultural heritage preservation, thus extending the applicability of the surface analytical techniques

Ultra Hydrophobic/Superhydrophilic Modified Cotton Textiles through Functionalized Diamond-Like Carbon Coatings for Self-Cleaning Applications

A stable and improved control of the wettability of textiles was obtained by using a coating of diamond like carbon (DLC) films on cotton by PECVD. By controlling different plasma pretreatments of argon, oxygen, and hydrogen on the cotton fibers' surface, we have shown that the pretreatments had a significant impact on wettability behavior resulting from an induced nanoscale roughness combined with an incorporation of selected functional groups. Upon subsequent deposition of diamond like carbon (DLC) films, the cotton fibers yield to a highly controlled chemical stability and hydrophobic state and could be used for self-cleaning applications. By controlling the nature of the plasma pretreatment we have shown that the oxygen plasma pretreatment was more effective than the argon and hydrogen for the superhydrophilic/ultra hydrophobic properties. The chemical and morphological changes of the cotton fibers under different treatments were characterized using X-ray photoelectron and Raman spectroscopy, AFM, and water contact angle measurements. The mechanism underlying the water-repellent properties of the cotton fibers provides a new and innovative pathway into the development of a range of advanced self-cleaning textiles

Introducing the HERACLES Ontology—Semantics for Cultural Heritage Management

Cultural Heritage (CH) (In the context of this paper, we consider cultural heritage built tangible cultural heritage, such as buildings or monuments.) is an important source of identity for humankind and needs to be conserved for future generations. Climate change (CC) will morph the environmental landscape, thus leading to climate stress imposed on CH. Experts from different domains, including, but not limited to, material scientists, conservators and managers of cultural heritage collaborate to find out how CC affects CH and how potentially harmful impacts can be mitigated. To find and understand correlations and effects of different factors, researchers collect and analyse vast amounts of data. Still, experts often cannot exchange or make efficient use of data since it often is unstructured, incompatible, or its plain existence is simply unknown. This article introduces means to achieve consent about available knowledge, to exploit synergy effects through the combination of available information and to provide a flexible multisource information platform in collaborative cultural heritage management projects. In the context of the European project HERACLES (HERACLES—HEritage Resilience Against CLimate Events on Site. Further information: http://www.heracles-project.eu/), an application-ontology was developed. The ontology facilitates reuse and integration of data through structuring and representing its semantics. The involvement in the HERACLES project guaranteed end-user driven development, practical results and encompassment of all domains represented in the project