LIBS analysis to define the alteration processes on the surface of ancient stones: the case study of Romanesque medieval monuments (Italy)

Weathering and bio-deterioration processes frequently affect the chromatic aspect of the stones used in the monuments. The surface alteration involves both physical modifications (e.g., increase of porosity) and chemical-mineralogical transformations of the rock, with formation of new secondary phases and deposition of the organic substances and inorganic solid phases (amorphous or crystalline particles). This research aims to study the surface films of stones (i.e., basalts, pyroclastic rocks, limestone, marbles) used in some historical-cultural relevant Sardinian Romanesque churches (XI-XIV sec.) using LIBS and XRD analysis. These latter, together with petrographic analysis by polarized light microscopy in thin section, are useful to reconstruct the micro-stratigraphic aspects of different film levels. The results highlight three different cases: i) chromatic alteration of the stone surface, ii) chemical-mineralogical alteration of stone with formation of coatings similar to the stone substrate, iii) chemical-mineralogical processes with the formation on the surface of secondary phases not related to the substrate, with the presence of Ca-oxalate (i.e. weddelite, whevellite). The presence of the Ca-oxalates, as noted in literature, is a testimony of application of organic substances on the surfaces themselves, with aesthetic purposes, to standardize or improve the color of the stone, or conservative, to limit the negative effects of weathering

PROTEUS: an immersive tool for exploring the world of cultural heritage across space and time scales

AbstractIn the field of digital humanities, it is increasingly necessary to develop and validate virtual reality tools that are capable of combining various scientific data in a virtualized context providing also access and user friendly consultation of online repositories. This paper reports the main aspects of the implementation of a virtual reality tool integrated with an online repository for storing 3D models, metadata and chemical analyses related to different sectors of digital humanities. The virtual reality software, developed for the Oculus Quest 2 hardware, is called PROTEUS and allows for seamless transition from the macroscopic world of digital humanities to the microscopic world of molecular sciences. The paper illustrates, by means of some case studies, the performances of this innovative tool that permits the researcher to understand and manipulate objects, to test hypotheses and to seek meaningful results, visualising the metadata while changing the parameters of the simulation in a dynamic and interactive way. This represents also a significant step forward in the democratisation of science, thanks to an user-friendly and immersive access to advanced scientific algorithms, which allow the natural perception of structural and topological features of the underlying molecular and supra-molecular systems. Graphical Abstrac

Mineralogical, petrographic and physical-mechanical study of Roman construction materials from the Maritime Theatre of Hadrian's Villa (Rome, Italy)

This paper presents the study of various Roman materials used in the construction of the Maritime Theatre, one of the main buildings in the Hadrian’s Villa complex, a designated UNESCO World Heritage Site located in Tivoli (Rome, Italy), dating to the first half of the II century A.D. The plaster layers (arriccio and intonachino) and overlying original Roman paintings that form the concave wall of the portico as well as some bedding mortars of the pyramidal stone elements (i.e. cubilia) of the circular masonry have been studied in particular. In addition, the acid volcanic rocks of the cubilia have been investigated, aiming to understand their state of alteration and geological origin. By mineralogical-petrographic microscopy (OM), diffractometry (XRPD), Raman spectroscopy, Point Load Tests (PLT), helium pycnometry, and particle size analysis, the composition and granulometric distribution of the aggregate, type and characteristics of the binder, and various physical-mechanical properties (density, porosity, water absorption, imbibition and saturation indices, mechanical resistance) of mortars and stones were defined. In addition, through digital image analysis of thin sections, the binder/aggregate ratio and some geometric characteristics of the aggregates (e.g. circularity) were determined. The research aims to improve the knowledge of the constructive technologies of the Maritime Theatre through the analysis of its materials

Coupling of electron and vibrational spectroscopy with false colour imaging for the investigation of natural dyes in historical fabrics (15th-18th centuries)

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Multivariate calibration in Laser-Induced Breakdown Spectroscopy quantitative analysis: The dangers of a ‘black box’ approach and how to avoid them

The introduction of multivariate calibration curve approach in Laser-Induced Breakdown Spectroscopy (LIBS) quantitative analysis has led to a general improvement of the LIBS analytical performances, since a multivariate approach allows to exploit the redundancy of elemental information that are typically present in a LIBS spectrum. Software packages implementing multivariate methods are available in the most diffused commercial and open source analytical programs; in most of the cases, the multivariate algorithms are robust against noise and operate in unsupervised mode. The reverse of the coin of the availability and ease of use of such packages is the (perceived) difficulty in assessing the reliability of the results obtained which often leads to the consideration of the multivariate algorithms as ‘black boxes’ whose inner mechanism is supposed to remain hidden to the user. In this paper, we will discuss the dangers of a ‘black box’ approach in LIBS multivariate analysis, and will discuss how to overcome them using the chemical-physical knowledge that is at the base of any LIBS quantitative analysis

A Multi-Analytical Study of an Ancient Egyptian Limestone Stele for Knowledge and Conservation Purposes: Recovering Hieroglyphs and Figurative Details by Image Analysis

A multi-analytical study was carried out on an ancient Egyptian limestone stele with red figures and hieroglyphs (S. 6145) coming from the village of Deir el-Medina and belonging to the collection of the Museo Egizio (Turin, Italy). With the support of a multidisciplinary team, a project for the preservation and conservation of this stele provided an opportunity to carry out a very detailed study of the object. Petrographic and mineralogical analysis led to the characterization and dating of the limestone, and ultrasonic tests were of great help in shedding light on the state of preservation of the stele, as a preliminary to planning conservation treatment. The chemical nature of the red pigment was investigated by non-invasive spectroscopic analyses. Multispectral imaging and statistical image processing improved the readability of the hieroglyphs, whose preservation ranged from heavily compromised to almost completely invisible, revealing some signs that had previously not been visible