Metrology for Cultural Heritage: multispectral 3D models by photogrammetry

L'abstract è presente nell'allegato / the abstract is in the attachmen

Editorial to selected papers from the IMEKO TC24 Special Issue "Measurements in Cultural Heritage"

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Atmospheric corrosion of outdoor bronze artefacts: The case study of 'Katarsis', by Magdalena Abakanowicz

The conservation of cultural heritage metallic items is deeply connected to the investigation of the corrosion phenomena affecting the metallic surface and to the study of the influence of the surrounding environmental parameters. This paper describes the case study regarding the metallic artwork 'Katarsis' of the Gori Art Collection at Fattoria di Celle (Pistoia, Italy), created by the artist Magdalena Abakanowicz. An in-situ multi-analytical approach was employed in order to assess the conservation state of the statues and to ensure their long-lasting preservation. In particular, X-rays fluorescence (XRF), Raman spectroscopy (RS), and X-Rays diffraction (XRD) were used for the identification of the corrosion products, mainly sulphates, and to identify the employed alloy. In this paper, the preliminary results will be presented and discussed

Nanoindentation and Raman spectroscopy measurements on dual-cure luting cement for dental conservative restoration

The employment of innovative all-ceramic materi-als and adhesive cement, as well as the development of new bonding procedures, allow clinicians to use minimally invasive approaches in conservative restorations. In particular, dual-cure cement allows for obtaining higher aesthetic and functional results. However, the reduced light transmission through ceramic materials could prevent the proper curing and affect the adhesion of these materials to the tooth surface. In this context, the development of an accurate measurement methodology to assess the extent of polymerization of dental resin-based luting cement and to correlate the conversion degree with the mechanical properties is of particular importance from the clinical and scientific point of view. A measurement approach that exploits Raman Spectroscopy and nano-hardness measurements is hereby proposed. In particular, in this study, two different light-curing protocols are employed on a dual-cure luting cement, usually used for the full-crown restoration of single-rooted teeth. The effect of different times and tack-curing steps on the polymerization shrinkage of resin-based luting cement is investigated. The pre-liminary results allow concluding that both curing protocols lead to a good polymerization, without significant differences in the degree of conversion along the cement-tooth interfacial surface, as proved by the almost constant ratio of the Raman vibration characteristic peaks. However, the nanoindentation modulus was lower in the case of the tack-cured protocol

Measurements for restorative dentistry: shrinkage and conversion degree of bulk-fill composites

The paper deals with a measuring approach based on Raman Spectroscopy and micro-CT imaging for correlating the degree of conversion of bulk-fill composites to the contraction shrinkage and consequently to the internal gap formation in high c-factor dental cavities. The developed study was performed on extracted molars in which a first-class cavity was prepared. A micro-CT scan was performed before and after composite lightcuring to tridimensionally measure the interfacial gap between the composite material and the cavity walls. After the complete polymerization of the composite, each sample was sectioned vertically to expose the lateral surface of the restorative material. Raman Spectroscopy measurements were performed along the cross-section of the cavity filled with the restorative material, every 0.5 mm from the occlusal surface. The obtained results showed a minimal gap opening after light-curing and a degree of conversion which was not affected by the bulk-fill composite thickness. Thanks to the 3D rendering, it should be observed that gaps were mostly concentrated at the cavity floor and despite the reduction in the degree of conversion detected in the deeper portions of the restoration, a three-dimensional opening of an interfacial gap was not observed. Therefore, it is possible to assume the presence of a correlation between the degree of conversion and the volumetric interfacial gap could. Further studies are actually in progress to compare these preliminary results with those obtained on other dental composite materials

A metrological approach for multispectral photogrammetry

This paper presents the design and development of a three-dimensional reference object for the metrological quality assessment of photogrammetry-based techniques, for application in the cultural heritage field. The reference object was 3D printed, with nominal manufacturing uncertainty of the order of 0.01 mm. The object has been realized as a dodecahedron, and in each face, a different pictorial preparation has been inserted. The preparations include several pigments, binders, and varnishes, to be representative of the materials and techniques used historically by artists. Since the reference object’s shape, size and uncertainty are known, it is possible to use this object as a reference to evaluate the quality of a 3D model from the metric point of view. In particular, verification of dimensional precision and accuracy are performed using the standard deviation on measurements acquired on the reference object and the final 3D model. In addition, the object can be used as a reference for UV-induced Visible Luminescence (UVL) acquisition, being the materials employed UV-fluorescent. Results obtained with visible-reflected and UVL images are presented and discussed

Characterization of the Santa Maria del Fiore Cupola construction tools using X-ray fluorescence

This paper presents the characterization of different tools employed in the construction of the Santa Maria del Fiore cathedral in Florence; they are part of the Opera di Santa Maria del Fiore collection and are currently exhibited in the Museo dell’Opera del Duomo. The analyzed objects are turnbuckles, pulleys, three-legged lewises, and pincers; indeed, despite their uniqueness and their importance from the historical point of view, this study is the first one that investigates their alloys composition. Actually, this information can be of great interest for curators to find the best conservation strategies and to have new insights on the production techniques typical of the Renaissance. The study was performed using X-Ray Fluorescence (XRF) in order to identify the materials constituting the objects. Then, XRF spectra were analyzed using chemometric techniques, namely Principal Components Analysis (PCA), in order to investigate possible similarities among different alloys and thus provide new indications to help collocating these tools in a specific historical period