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Metrology for Cultural Heritage: multispectral 3D models by photogrammetry
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Editorial to selected papers from the IMEKO TC24 Special Issue "Measurements in Cultural Heritage"
Full text linkNanoindentation and Raman spectroscopy measurements on dual-cure luting cement for dental conservative restoration
Full text linkThe 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
Improvements to the analytical protocol of lapis lazuli provenance: First study on Myanmar rock samples
Full text linkThe study of lapis lazuli is important to find out information about the provenance of a materialused since the Neolithic Age for the manufacturing of precious carved artefacts. The Badakhshan depositsin Afghanistan are commonly considered as the main source of lapis lazuli in ancient times. However, otherquarries could have possibly been exploited since antiquity. A protocol to distinguish the provenance oflapis lazuli rocks among four known source areas (located in present-day Afghanistan, Tajikistan, Siberiaand Chile) by means of non-invasive techniques was set up in the last years. It is based on differences in thephysical-chemical properties measured in 45 lapis lazuli rocks that constitute our reference database. Theaim of the present paper is to extend the protocol analysing, by means of a multi-analytical approach, 10lapis lazuli rock samples, coming from the quarry district of Mandalay in Myanmar, to find out significantpetrographic and mineralogical markers. Optical microscopy and scanning electron microscopy were usedto perform a detailed petrographic and mineralogical characterisation allowing to distinguish the Myanmarlapis lazuli in three main groups. SEM-EDX analyses on selected mineral phases were performed
A trustable multispectral photogrammetry pipeline for the reproduction of noncollaborative materials
Full text linkMany non-invasive techniques are now widely available to experts for the study and understanding of real objects, encouraging the development of new low-cost survey tools. The opportunity to create digital twins opens up many possibilities for in-depth study of art objects. In particular, the increasing adoption of photogrammetry and multispectral reflectography in the field of cultural heritage has provided art historians, conservators and conservation scientists with precise tools for the study of pigments and artistic techniques, facilitating the attribution and dating of art-historical artifacts [1]. Photogrammetry has established itself over time as one of the most common modern survey tools, distinguished by its ease of implementation and ability to obtain metrologically reliable and photo-realistic three-dimensional models in a quick and cost-effective way [2]. Although its use is currently quite popular, certain limits prevent its proper application in the field of cultural heritage, especially in the presence of objects made of shiny, reflective materials such as metals. In recent times, the use of polarized light in the 3D field exploiting the Physically Based Rendering has also provided encouraging insights into the use of photogrammetry even in the presence of non-cooperative materials, expanding the application range and improving the resemblance to the real object [3]. Furthermore, the possibility of producing three-dimensional models integrating data from other spectral bands (UV/IR luminescence and reflectography) and other diagnostic techniques (XRF, RAMAN etc.) opens up new perspectives in the study of constituting materials, allowing information to be combined in a three-dimensional model of more immediate consultation. This work presents a workflow that addresses the various issues and combines them into a single threedimensional model that is correct in size and color, light and easy to consult thanks to the use of free, cross platform visualization tools.The chosen case study, a Chinese gold statuette depicting Buddha, general chronology 6th century BCE, holds many interesting enigmas by addressing the limitations imposed by photogrammetry and integrating data from different techniques into a single three-dimensional model that can be navigated online
Characterization of Early 20th Century Measurement Instruments: A Heritage Approach
Full text linkA conservation campaign is currently underway, at Politecnico di Torino, to preserve a significant collection of measurement instruments and devices from the Department of Physics and the Advanced School of Electronics Laboratory, originally established by Galileo Ferraris in 1888. The collection comprises teaching and research apparatus used between the 1920s and 1960s, including voltmeters, ammeters, galvanometers, valve and battery testers, and other related equipment. The ongoing conservation effort utilizes non-invasive, in situ analytical techniques such as portable X-ray fluorescence (XRF), Raman spectroscopy, and multiband photogrammetry. These methods have enabled detailed examination of the materials and their degradation processes without compromising the integrity of the artifacts. Preliminary analyses have revealed a variety of corrosion morphologies, attributable to the use of different base metals, iron, copper, silver alloys and to variable environmental conditions over time. Galvanic corrosion is a frequent finding, particularly in areas where Cu-based and Fe-based alloys or gilded components, are in direct contact. Cross-polarized and Ultraviolet-Induced Luminescence Photogrammetry are being employed to generate detailed 3D models of the instruments, supporting both documentation and future conservation planning
Electrochemical Impedance Spectroscopy System Based on a Teensy Board
Full text linkThis article describes a portable low-cost device for performing electrochemical impedance spectroscopy (EIS) measurements, which is based on an off-the-shelf TeensyDuino. The instrument does not make use of other components, such as operational amplifiers, so it can be readily set up by anyone having a Teensy device and some resistors. Teensy 3.2, Teensy 3.5, and Teensy 3.6 can be used to realize the EIS system. The instrument can measure the impedance in the frequency range from 0.01 to 50 000 Hz, and by selecting the shunt resistor, it can be adapted to different impedance values. No special instrumentation is required for the system calibration. The proposed system uncertainty is less than 5% for an impedance of up to 50 kΩ , a value which is lower than the usual intrinsic uncertainty of most corrosion experiments
Atmospheric corrosion of outdoor bronze artefacts: The case study of 'Katarsis', by Magdalena Abakanowicz
Full text linkThe 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
Measurements for restorative dentistry: shrinkage and conversion degree of bulk-fill composites
Full text linkThe 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
An improved methodology for extending the applicability of Reflectance Transformation Imaging to confined sites
No full textRecent advances in the field of imaging
technologies rapidly spread new methods of representing
cultural heritage, expanding the possibilities for art
historians, archaeologists, conservators and conservation
scientists. In this regard, Reflectance Transformation
Imaging (RTI) and three-dimensional (3D) modeling
using close-range photogrammetry have become
rapidly common and widely used by an heterogeneous
public, multiplying the possibilities of understanding
artworks from different points of view. This paper discusses
the results that were achieved by applying these
techniques to better understand the surface of a basrelief
owned by the Museo Egizio of Turin (Italy) in a
confined site. We were able to successfully enhance the
volume of engravings by integrating both RTI and 3D
visualization to obtain a new investigation tool with a
more suitable illumination
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