Multispectral analysis of Nuragic metallic samples (Sardinia, Italy)

ABSTRACT: In this investigation, a protocol combining the use of Monte Carlo simulations together with energy-dispersive X-ray fluorescence (ED-XRF) analysis was used to determine the chemical composition of a set of nine objects from a private collection, apprehended by Carabinieri and without archaeological context. The artefacts are thought to belong to the nuragic period from Sardinia, Italy. The protocol employed is a powerful and non-destructive method useful for cultural heritage applications where usually no sampling is allowed and was applied here with the objective of attesting the authenticity of the objects. The samples were simulated as multilayered structures composed of bulk material and outer corrosion layer so the patina thickness and composition could be estimated as well by the Xray Monte Carlo (XRMC) package. The method proved useful and powerful, capable of efficiently determining the composition and structure of most of the objects in a total nondestructive approach, attesting the existence of at least one fake in the set. Nevertheless, for a more throughout evaluation and a better estimation of the patina composition, the use of complementary analytical techniques has shown required

Modular ma-xrf scanner development in the multi-analytical characterisation of a 17th century Azulejo from Portugal†

This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 766311, from Regione Lazio, under the Project "MUSA" n. B86C17000280002, of the Excellence Centre at the Lazio Technological District for Cultural Heritage (DTC), from the Regione Autonoma di Sardegna, under project number CUP:J81G17000140002, and from Fundacao para a Ciencia e a Tecnologia, grants UID/FIS/04559/2020 and UIDB/00729/2020.A modular X-ray scanning system was developed, to fill in the gap between portable instruments (with a limited analytical area) and mobile instruments (with large analytical areas, and sometimes bulky and difficult to transport). The scanner has been compared to a commercial tabletop instrument, by analysing a Portuguese tile (azulejo) from the 17th century. Complementary techniques were used to achieve a throughout characterisation of the sample in a complete non-destructive approach. The complexity of the acquired X-ray fluorescence (XRF) spectra, due to inherent sample stratigraphy, has been resolved using Monte Carlo simulations, and Raman spectroscopy, as the most suitable technique to complement the analysis of azulejos colours, yielding satisfactory results. The colouring agents were identified as cobalt blue and a Zn-modified Naples-yellow. The stratigraphy of the area under study was partially modelled with Monte Carlo simulations. The scanners performance has been compared by evaluating the images outputs and the global spectrum.publishersversionpublishe

Testing the accuracy of the calculation of gold leaf thickness by MC simulations and MA-XRF scanning

The use of X-ray fluorescence (XRF) scanning systems has become a common practice in many application sectors. In multistratified and heterogeneous samples, the simple analysis of an XRF spectrum as a response of the entire sample is not reliable, so different spectral analysis techniques have been proposed to detect the presence of surface stratification. One commonly studied case is that of gilding, i.e., the presence of a superimposing gold-leaf layer. The observation of changes in the net peak ratios of a single element or of several elements in an XRF spectrum is a well-developed practice, but is still not used in the case of XRF scanning (macro-X-Ray fluorescence scanning, MA-XRF), a technique that can be described as the extrapolation of XRF spot analysis to a second dimension, scanning a sample surface instead. This practice can yield information on the overlaying layer thickness, if some properties of the sample are known—or estimated—beforehand, e.g., the overlapping layer’s chemical composition and the matrix effect contribution from the bulk material (thick ratio). This work proposes the use of an algorithm to calculate the thickness distribution of a superimposing gold layer accurately and automatically through the differential attenuation method by using MA-XRF datasets in a total noninvasive manner. This approach has the clear advantage over the traditional spot sampling of allowing the generation of a surface heightmap to better visualize and interpret the data, as well as a considerably larger sample space. Monte Carlo simulations were used to verify the influence of the medium used to adhere the gold leaves to the substrate and to generate known spectra to assess the algorithm’s accuracy

Development of a 2D-XRF scanner for cultural heritage applications

In this work, the design conception and the construction of a 2D X-ray fluorescence scanner, from mechanical parts to software, are fully presented and discussed. The instrument is composed of one modular scanning head, with interchangeable parts and two different X-Y translation stages. It is controlled by one single program, using specifically tailored Application Programming Interfaces (APIs). The system design follows a plug-and-play approach, where the system can adapt to almost every need, being transported to galleries, and even overseas to remote excavation sites. A complete and open-source data analysis software for Windows™, XISMuS, was also developed and is available online with a distribution package. The software design and implementation are also fully described in this work, as well as its functionalities and a copy of the User Guide for version v2.4.3. The fully constructed instrument and the data analysis software were tested against one commercial model and on a wide variety of materials, in combination with several different analytical techniques for a full characterization of tiles, painted leathers, metals, gildings, stones, sediments, and paintings. All the case studies are thoroughly presented. Among them, an innovative method, which combines micro-petrography and XRF scans of thin sections performed in-field at Koumasa, Crete

Monte Carlo simulations of ED-XRF spectra as an authentication tool for nuragic bronzes

The high artistic and cultural relevance of particular objects, in this case from the Nuragic civilization, have stimulated the growth of a forgery industry, replicating small bronze boats (navicelle), statues (bronzetti), and other objects. It is often the case where the forgeries are of such quality that it becomes difficult to distinguish them from authentic artifacts without a proper chemical analysis. In this research, a Monte Carlo simulation algorithm for X-ray interactions with matter is used to obtain the chemical composition from the bulk of each object from a set of five. The method employed has the advantage of being completely nondestructive and relatively fast. The objects’ chemical composition and morphology were compared with the data available from authentic artifacts so their authenticity could be inferred. Four of the five objects are likely to be authentic, where two of them could be associated with a Sardinian origin

Recent developments on portable XRF scanner

A prototype X-ray fluorescence (XRF) scanner was developed with the aim of being reliable and portable, best suiting the needs of cultural heritage scientists who constantly face the difficulty of in-situ analysis. The instrument constructed is composed of an exchangeable scanning head (X-ray tube and detector), a motorized x-y stage with a controlling interface and a laptop. With the small stage, it can scan areas up to 20 x 20 cm 2 with a lateral resolution of 1 mm. The system can be transported inside a standard airplane cabin trolley and weights no more than 10 Kg. The controlling interface was programmed in LabView© and the data evaluation is performed on-the-go with a custom-made algorithm. The system has been put to test with a variety of materials and some results are discussed

Compósitos híbridos de polietileno de alta densidade carregados com Óxido de alumínio e reforçados com fibra de vidro

Compósitos híbridos poliméricos têm sido desenvolvidos visando a obtenção de propriedades de desempenho diferenciadas. Com essa finalidade compósitos de polietileno de alta densidade (PEAD) carregados com alumina e com reforço híbrido de alumina e teores variáveis de fibra de vidro foram processados em extrusora de rosca dupla. As propriedades mecânicas dos materiais foram determinadas de acordo com a ASTM D-1238. O comportamento térmico foi analisadoatravés de técnicas convencionais. A morfologia foi investigada através de microscopia eletrônica de varredura. Os resultados obtidos demonstraram que a alumina não promoveu o aumento da estabilidade térmica do PEAD e que houve formação de aglomerados com o aumento do teor de alumina. Os compósitos híbridos apresentaram aumento significativo do Módulo de Young e da tensão de escoamento. As micrografias dos compósitos formulados com 12% v/v de alumina e 8,5% v/v de fibra de vidro evidenciaram umaorientação das fibras de vidro responsável pelas propriedades mecânicas superiores.Polymer hybrid composites have been developed in order to obtain superior performance properties. In this context, composites of high density polyethylene (HDPE) filled with alumina and with hybrid reinforcement of alumina and a variable content of glass fiber were processed in a twin screw extruder. The mechanical properties of the obtained materials were determined according to ASTM D-1238. The thermal behavior was analyzed by conventional techniques. The morphology was investigated by scanning electron microscopy. The results showed that there was no increase of the thermal stability of HDPE with the addition of alumina.The formation of agglomerates with the increase of alumina content was evidenced. The hybrid composites showed significant increase in the Young's modulus and in the yield stress. The micrographs of composites processed with 12 vol% of alumina and 8,5% vol of glass fiber showed that there was an orientation of the glass fibers.This microstructure is responsible by the best mechanical properties

Diagnostic studies on Nuragic bronzes from Sardinia using a Monte Carlo protocol

In this investigation, a protocol combining the use of Monte Carlo simulations together with energydispersive X-ray fluorescence (EDXRF) analysis was used to determine the chemical composition of a set of objects from a private collection, apprehended by Carabinieri and without archaeological context. The artefacts are thought to belong to the Nuragic period from Sardinia, Italy (~1500 BCE to 500 CE). The protocol employed is a powerful and non-destructive method useful for cultural heritage applications where usually no sampling is allowed. The protocol digitally recreates the objects surface and generates random photons to interact with the volume. It was herein applied with the main objective of attesting the authenticity of the objects. The samples were simulated as multi-layered structures composed of bulk material and outer corrosion layer so the patina thickness and composition could be estimated as well by the X-ray Monte Carlo (XRMC) package. The method proved useful and powerful, capable of efficiently determining the composition and structure of most of the objects in a total non-destructive approach, attesting the existence of at least one fake in the set. Nevertheless, for a more throughout evaluation and a better estimation of the patina composition, the use of complementary non-destructive analytical techniques and further enhancements in the code package have shown to be required

Mechanical and thermal properties of high-density polyethylene/alumina/glass fiber hybrid composites

In this investigation, composite materials made from high-density polyethylene (HDPE) and alumina, as well as from HDPE, alumina, and glass fibers, were prepared, aiming to improve the thermal stability, stiffness, and mechanical strength. The combined effects of alumina and glass fibers and the individual effects of alumina were studied. Alumina concentrations ranged from 5 wt\% to 10 wt\% and glass fiber concentrations ranged from 10 wt\% to 30 wt\%. For the hybrid composite materials, alumina concentration was maintained constant as the glass fiber concentration increased. The composites were processed with a double-screw extruder. Their properties were evaluated through a multi-analytical approach. Results pointed to a significant increase of the elastic modulus for the hybrid composite (up to 501\% in comparison to the neat polymer), at the cost of a large decrease in toughness, alongside a decline in impact resistance. Elastic modulus improvement was observed in both hybrid and HDPE-alumina composites, being higher for the hybrid composites due to the addition of glass fibers. HDPE-alumina composites presented a decrease in mechanical strength, whereas the hybrid composites showed an increase of this parameter. Concerning thermal properties, the hybrid composites presented higher thermal stability than that of the HDPE-alumina composites and a similar degradation temperature as the neat polymer. Micrographs pointed to weak adhesion between alumina particles and the polymeric matrix as well as a slight degree of fiber detachment. Overall, the hybrid composites presented considerably higher stiffness and mechanical strength than the neat polymer and HDPE-alumina composite (19–26\% increase), with no significant change in thermal stability

Characterisation of Alloy Composition of Protohistoric Small Boat Models from Sardinia (Italy)

The Sardinian protohistoric civilisation (Final Bronze Age and the Early Iron Age) has greatly contributed to the development of metallurgy in the Mediterranean area by producing a large number of bronze artefacts. Among them, small boat models (so-called “navicelle”) represent one of the most characteristic objects from the Sardinian Protohistoric civilisation. This work is an attempt to classify these boats on the basis of their alloy composition, provenience, and morphology. Due to the impossibility of removing the boats from the museum, alloys were characterised using energy-dispersive X-ray fluorescence spectrometry and Monte Carlo simulations. Fifteen boats were analyzed. Obtained results were compared to other performed analyses in the last few decades with different techniques and reported in the literature. Analyses allow for characterising both the bulk composition of ternary alloy Cu–Sn–Pb and patina thickness, offering useful information about their conservation status and the technological achievements of Sardinian craftsmen, while also providing information on smelting temperatures and casting techniques