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A Bodhisattva Avaloktesvara from the 15th century (collection of Rietberg Museum, Zurich). Left: photograph; and right: neutron radiography showing devotional objects on the inside of the sculpture
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The use of non-invasive and non-destructive methods is highly relevant for cultural heritage objects in particular, due to their uniqueness and the often high cost of material as well as immaterial value. It is, however, of great importance to gain a simple overview of their material distribution, the manufacturing techniques, the provenance and th...
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... with the rotation stage. Two datasets, each of 1125 projections over 360°, were acquired: one for the sculpture’s head section and another for its base section. After the reconstruction, the two resulting sets of tomograms were combined into one global one by interpolation of the overlapping areas. The evaluation of the volume data allowed the different materials within the sculpture to be segmented. It allowed the areas affected by carbonation to be assessed, determining the shape of almost the entire wood kernel and localising the nails and soldering material used to fix the sheets onto the sculpture (Figure 2). Although information on the greatest part is available, some areas cannot be described appropriately. These are areas lying in concave regions of the sculpture, such as the area between the trousers or in front of the chest near the bent elbow, and are therefore never, or only in very few angles, directly visible in the projections. The 3D data allowed mapping of not only the fixing points of the lead sheath but the corroded areas (Figure 1(c)) especially. This information is relevant for understanding the dynamics of this specific pathology. Altogether, the investigation yielded crucial information for the development and planning of strategies for the indispensable restoration and conservation of this piece of art. Safekeeping, preservation, conservation and restoration are very important topics when dealing with cultural heritage objects. Here, not only the actual condition of an object is important but also the development of new techniques, allowing for better restoration or conservation of the objects. One still on-going study, which is being carried out by PSI in collaboration with the Swiss National Museum, is focusing on the improvement of conservation treatments for corroded iron objects. Archaeological iron artefacts often build up high chloride contents, especially when they are buried in soil. One prominent chloride-containing corrosion product is akaganeite (beta- FeO(OH,Cl)), which forms a very unstable corrosion layer. After excavation, the high concentration of chlorides in addition to the presence of humidity and oxygen can cause the complete decay of the iron objects. In order to stabilise the iron objects, either the chlorides, oxygen or water must be completely removed from the system. As storage in oxygen or humidity-free environments is not feasible under standard museum conditions, the aim of modern iron conservation is to remove the chlorides within the iron objects. This can be achieved using the method of iron desalinisation [18,19] . The impact of this treatment is nevertheless hard to validate, as the condition within the object has to be monitored before and after the treatment, which entails, with standard methods, the destruction of the sample. The goal of the joint project with the Swiss National Museum is to determine the impact of the desalinisation treatment on heavily- corroded iron nails. In the preliminary investigation presented, the applicability of neutron imaging to discern and assess regions with differing corrosion products is demonstrated. Besides the akaganeite, other corrosion products can be present, such as magnetite (Fe 3 O 4 ), maghemite (Fe 2 O 3 ) or goethite (FeO(OH)). These iron compounds already show clear differences concerning their theoretical attenuation coefficients for neutrons (Table 1). The test objects were examined by means of neutron microtomography [17] . The first results are shown in Figure 3. Here, regions with different grey levels and thus attenuation can be discerned. Although these regions could not yet be assigned to certain corrosion products, the results prove the suitability of the method for such an investigation. In the next step, the corroded objects will be desalinised and, after the treatment, re-examined by means of neutron imaging in order to assess the efficiency of the treatment. Together with the treated objects, material samples of different corrosion products will be examined in order to obtain a calibration for the different materials and to be able to confirm the identity of different regions. One field of research where neutron imaging proved to be especially useful is concerned with the examination of bronze sculptures [21,22] . Interesting here, for example, are Buddhist bronze figures, which often feature devotional objects placed within the sculpture. As shown before by Lehmann et al [23] , neutrons are the only option for such investigations as X-rays fail due to a limited contrast and too low a transmission. The big advantage of neutron imaging in this example is the high penetrability of metal combined with a high sensitivity for hydrogen and hence organic material. This enables the metal of the sculpture to be penetrated and allows the devotional objects within the sculpture, which consist to a great extent of organic material, to be visualised and thus yield good contrast in the neutron image. Figure 4 shows a 15th century Bodhisattva Avaloktesvara from the collection of the Rietberg Museum in Zurich. In the frontal radiography of the sculpture, inner features can already be distinguished. Several shapes can be made out within the sculpture, but it is not possible to retrieve in-depth information on the exact position and shape of the objects. The reconstructed volume data allows for a closer inspection and description of the objects (Figure 5). Segmentation also allows the objects to be virtually retrieved and studied separately from all sides (Figure 5(c)). In the void within the sculpture, three major features are noticeable. One is a scroll tied up with cord. The scroll was inserted along the vertical axis of the inner void and probably contains some religious text (for example prayer, mantras, etc). Another feature is a small heart-shaped object in the chest of the sculpture. It appears to be a kind of small capsule tightly wrapped in a piece of cloth and tied up with string. The capsule itself features another void, which is partially filled with a less attenuating material than the capsule wall. The third object seems to be a small pouch containing a couple of smaller spherical objects. The pouch itself is convoluted and tied up with another piece of string. Besides standard transmission-based neutron imaging, more advanced imaging methods, such as the energy-selective neutron imaging or Bragg-edge imaging, can also be used successfully to investigate cultural heritage topics. In a joint research project with the University of Zurich and the Swiss National Museum, bronze blades found in Wollishofen, near Zurich, were studied with respect to their manufacturing process (Figure 6). Standard crystallographic analyses are carried out through the interpretation of the metallographic structure. These analyses lead to conclusions regarding the mechanical and thermal processes a metal object is exposed to in the course of its production, use and different post-usage formation processes. In turn, this allows the technological know-how and skills of a prehistoric society, the identification of individual and specific workshop production methods, as well as the actual functionality and use of the objects to be revealed. Traditional metallographic analyses, however, require the cutting and/or abrasion and thus the (partial) destruction of these objects with a cultural-historical value. This partial destruction is the reason that such kinds of investigation are very seldom conducted. The availability of a method to non-destructively assess information on the crystalline structure of such delicate and precious objects would allow a much larger database to be established, thus providing a representative starting point for plausible discussion and interpretation of the prehistoric bronze craft. The scope of the presented project is the reconstruction of the manufacturing process of prehistoric bronze blades. For this purpose, the crystalline structures and textures of original 3000 year-old prehistoric blades should be compared with blades manufactured using experimental archaeology. In a preliminary test study, one original blade and one replica were investigated using energy-selective imaging. This test was only intended as a proof of principle: whether it would be possible to discern different regions within the blades. Using a velocity selector narrowing down the utilised neutron energy spectrum to 15%Δλ/λ, energy scans of the blades were performed in 0.1 Å-steps for neutron spectra with mean neutron wavelengths between 3 Å and 5 Å. While the knives appear homogeneous in radiography images using a polychromatic beam, contrasts within the blades vary considerably depending on the selected neutron energy. Darker areas corresponding to regions with higher attenuation ( ie fewer neutrons arriving on the detector) due to Bragg scattering on the crystal lattice are most pronounced for certain wavelengths and disappear with modification of the used energy (Figure 7). This energy scan was used to choose the mean energy providing most contrast (at 3.5 Å), which was subsequently used to perform an energy-selective neutron tomography. The reconstruction showed a clear structural bipartition in both blades, caused by differences in the crystalline structures of the bronze (Figure 8). The replicated blade had been forged in the area of the cutting edge only; here, the material shows only small contrast changes and appears almost homogeneous. The back of the knife had been left in its cast state and features strong contrast changes due to Bragg scattering, hinting at larger structures (such as crystallites). The blades mainly differ in voids occurring in the replica and visible as dark circles in the tomogram. The striking concurrence of the images of the replica and the archaeological bronze knife leads to the conclusion that the Bronze Age knife must have been worked on, for the most part, in the same way as ...
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The methodical progress in the field of neutron imaging is visible in general but on different levels in the particular labs. Consequently, the access to most suitable beam ports, the usage of advanced imaging detector systems and the professional image processing made the technique competitive to other non-destructive tools like X-ray imaging. Bas...
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... In archaeometric studies, neutron imaging and diffraction methods are able to read the imprint left at different levels of the crystalline structure by distinctive manufacturing processes or by other actions that occurred during the life cycle of an item, i.e., mechanical and thermal impact, recycling and modern intervention [14][15][16][17]. ...
Antique swords from the pre-colonial West African kingdom of Dahomey are aesthetically unique, but they also have many design features inspired by swords from Europe, the Islamic world and elsewhere. As the kingdom was famous for importing luxury European objects, this study aimed to pinpoint evidence of Dahomean sword composition and manufacture to determine scientifically whether they were being made in Dahomey, or imported. An inter-disciplinary team made up of historical archaeologists and neutron scientists examined six 19th century Dahomean swords, using a non-invasive multi-methodological approach based on neutron tomography, powder diffraction full pattern analysis and diffraction residual stress measurements. The findings suggest that, despite their foreign design influences, not only were these striking heritage objects made in Africa, they may also have been likely made from locally smelted iron–something that contradicts the assumptions of the few existing historical reports. This has important implications for studies on the kingdom, and also helps to further the long-standing debate surrounding European iron imports—not just within Dahomey, but throughout the wider West African region.
... Unlike traditional X-ray imaging, neutron tomography offers enhanced penetration capabilities for metallic objects and is highly sensitive to hydrogenous materials. It is ideal for visualizing organic components and corrosion products within metal artifacts [17,18]. This capability facilitates a comprehensive examination of the artifact's internal composition, corrosion patterns, and any embedded organic materials or residues, thereby offering a more complete understanding of the artifact's condition and history. ...
This study presents a preliminary examination of the effects of environment changes post-excavation on heavily corroded archaeological Roman iron nails using neutron tomography and image registration techniques. Roman nails were exposed to either a high relative humidity environment, or fast thermal drying as primary experiments to show the power of this imaging technique to monitor and quantify the structural changes of corroded metal artifacts. This research employed a series of pre- and post-treatment tomography acquisitions (time-series) complemented by advanced image registration methods. Based on mutual information (MI) metrics, we performed rigid body and affine image registrations to meticulously account for sample repositioning challenges and variations in imaging parameters. Using non-affine local registration results, in a second step, we detected localized expansion and shrinkage in the samples attributable to imposed environmental changes. Specifically, we observed local shrinkage on the nail that was dried, mostly in their Transformed Medium (TM), the outer layer where corrosion products are cementing soil and sand particles. Conversely, the sample subjected to high relative humidity environment exhibited localized expansion, with varying degrees of change across different regions. This work highlights the efficacy of our registration techniques in accommodating manual removal or loss of extraneous material (loosely adhering soil and TM layers around the nails) post-initial tomography, successfully capturing local structural changes with high precision. Using differential analysis on the accurately registered samples we could also detect and volumetrically quantify the variation in moisture and detect changes in active corrosion sites (ACS) in the sample. These preliminary experiments allowed us to advance and optimize the application of a neutron tomography and image registration workflow for future, more advanced experiments such as humidity fluctuations, corrosion removal through micro-blasting, dechlorination and other stabilization treatments.
... These methods are experimental approaches that simultaneously ensure the physical safety of the studied objects, and obtain most complete information about those phase compositions, a presence of internal defects, and the structural features. The structural data obtained during those studies makes it possible to determine the place of creation of one or the other historical artifacts [2], to establish the age, manufacturing technologies, the degree of preservation of the object [3,4], to found the hidden defects [5,6], to clarify the technique of the crafter, to develop an optimal method for restoration [7]. It should be noted that the processes of cultural or social changes in certain stages of the historical evolution of specific groups of the population are most clearly reflected in changes in the technologies of processing and producing of metal objects and, especially, the weapons. ...
The spatial distribution of a corrosion in the volume of bronze knife discovered during archaeological excavations in the Quyun archaeological site, belonging to the Burgulyuk archaeological culture, as well as an iron knife found during work on the medieval site of Shodmalik-ota, was studied using the neutron radiography and tomography methods. Both archaeological sites are located in the Tashkent region of Uzbekistan. As a result of the research, the three-dimensional model of a bronze knife was reconstructed from neutron tomography data. A penetration of corrosion into the volume of this knife was analyzed. Several rounded cavities with an average size of 1.5(2) mm were found in the thickness of the blade of the bronze knife. From the reconstructed neutron tomography data, the structural features of the iron knife were revealed, and the corresponding volumes occupied by corrosion products were segmented from the total volume of the knife. It is established that the volume of corrosion is 338.77(1) mm3 or 17.7% of the total volume of the iron knife.
... Thanks to the penetration power and the non-invasive nature of X-rays, CT enables the complete imaging of precious objects. Archaeometric analysis can also be carried out with neutrons for imaging or for material characterization [10,11], successfully applied to cultural heritage for various kind of finds, e.g., Egyptian metallic inks on textiles [12], metallic objects, or other archeological items [13]. ...
X-ray Computed Tomography (CT), a commonly used technique in a wide variety of research fields, nowadays represents a unique and powerful procedure to discover, reveal and preserve a fundamental part of our patrimony: ancient handwritten documents. For modern and well-preserved ones, traditional document scanning systems are suitable for their correct digitization, and, consequently, for their preservation; however, the digitization of ancient, fragile and damaged manuscripts is still a formidable challenge for conservators. The X-ray tomographic approach has already proven its effectiveness in data acquisition, but the algorithmic steps from tomographic images to real page-by-page extraction and reading are still a difficult undertaking. In this work, we propose a new procedure for the segmentation of single pages from the 3D tomographic data of closed historical manuscripts, based on geometric features and flood fill methods. The achieved results prove the capability of the methodology in segmenting the different pages recorded starting from the whole CT acquired volume.
... Neutron Imaging (NI), such as radiography and tomography, are testing methods which can be used to determine the inner structure of the investigated objects. The study of the morphology and internal volumes is useful for the determination of the manufacturing processes, provenance, dating, and information about the state of conservation and restoration in the cultural heritage field [3][4][5][6]. The NI techniques exploit the interaction of the incoming neutron beam with the object under investigation. ...
... These methods convert radiographic data into compressed information with the help of dedicated software tools. Due to the interaction processes of neutrons with the matter, they are considered an ideal probe for the non-destructive and non-invasive investigation of cultural heritage objects [3][4][5][6][7][8][9][10][11][12][13]. Indeed, neutrons interact with the atomic nuclei with a penetration depth of incident beam that is a function of the sample: for metal alloys, pottery, and stones they access the bulk of the objects without substantial attenuation while they are highly sensitive to light elements such as hydrogen [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. ...
... Due to the interaction processes of neutrons with the matter, they are considered an ideal probe for the non-destructive and non-invasive investigation of cultural heritage objects [3][4][5][6][7][8][9][10][11][12][13]. Indeed, neutrons interact with the atomic nuclei with a penetration depth of incident beam that is a function of the sample: for metal alloys, pottery, and stones they access the bulk of the objects without substantial attenuation while they are highly sensitive to light elements such as hydrogen [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Significant progress has been made regarding spatial and temporal resolutions, achieved in different ways such as the optimization of the optical camera that collects the signal from the scintillator screen [19] and the use of axisymmetric grazing-incidence focusing mirrors [20,21], transforming pinhole cameras into microscopes. ...
Recently, learning algorithms such as Convolutional Neural Networks have been successfully applied in different stages of data processing from the acquisition to the data analysis in the imaging context. The aim of these algorithms is the dimensionality of data reduction and the computational effort, to find benchmarks and extract features, to improve the resolution, and reproducibility performances of the imaging data. Currently, no Neutron Imaging combined with learning algorithms was applied on cultural heritage domain, but future applications could help to solve challenges of this research field. Here, a review of pioneering works to exploit the use of Machine Learning and Deep Learning models applied to X-ray imaging and Neutron Imaging data processing is reported, spanning from biomedicine, microbiology, and materials science to give new perspectives on future cultural heritage applications.
... With the development of new technologies and the increasingly important presence in the research of analysis algorithms, classification and segmentation techniques have become increasingly routine. In some sectors such as diagnostics applied to cultural heritage [10][11][12][13][14][15][16], segmentation techniques, sometimes even very advanced ones, are on the agenda [17][18][19][20][21]. In the field of geomaterials, there are several applications of image segmentation analysis, especially as regards the identification, classification, and quantification of iron ore [4,5,[22][23][24][25]. ...
Often when we approach the study of lithologies coming from the urban environment, but in general, even from any other environment, be it a quarry, a mine, an outcrop of our interest, the first study we carry out is the one in reflected-light optical-microscopy. Reflected-light microscopy in respect to transmitted-light microscopy requires minimal sample preparation, having to polish a single surface and without the need to thin the samples to allow light to pass through them. It may be useful, already in the first analysis, to try to produce quantitative data on what we are observing. A further advantage of reflected light in an urban environment is that of being able to observe and describe the formation or interaction between opaque minerals and the environment. Information that we lose by passing directly to the transmitted light. The information that can be useful to us and that we can obtain are the relative porosity of the sample, the texture (when easily recognizable in reflected light), the maximum size and shape of the edges of the grains. To all this is added the relationship between the areas of the different crystallites identified and the possible background mass, which cannot be solved on the observation scale. When we are dealing with many samples, we do not always have the time to be able to study individually sample by sample through images, so we resort to the use of image analysis tools for image segmentation and analysis. Among these, the main thresholding method with the Otsu method, the segmentation with the k averages algorithm, and, finally, a neural network of the SOM type. In this short work, we will review the main methods of image segmentation plus an innovative method developed by our group, highlighting its strengths and weaknesses.
... One of the important directions to be developed at the new neutron facility is the non-destructive neutron analysis of the cultural heritage objects [26]. The ancient Uzbekistan cultural place was an important trading center on the ancient Silk Route, and the Uzbek nation is a rich mixture of different cultures, as a result of the clash of civilizations. ...
The goal of this article is to describe the new neutron imaging facility constructed on the 5th radial beamline of the WWR-SM research reactor at the Institute of Nuclear Physics of the Academy of Sciences of the Republic of Uzbekistan (Tashkent, Republic of Uzbekistan). The neutron beam with the dimensions of 90 × 90 mm² is formed by the collimator system, the characteristic parameter L/D is 600. The two mirror detector system is based on the ⁶LiF/Zn(Cd)S:Ag scintillation screen and the high-resolution ProLine PL-09000 CCD camera. The design of the experimental facility, the main parameters, and recently obtained results of the neutron radiography and tomography experiments are presented.
... A metallographic analysis would be sufficient to determine the authentic artefacts but this destructive practice is not acceptable for museum objects, so that only a non-invasive approach can be employed. In archaeometric studies, neutron imaging and diffraction methods are able to read the imprint left at different level of the crystalline structure by distinctive manufacturing processes [18][19][20][21][22][23]. These analytical tools can be applied to disclose the true nature of museum arms and armor. ...
This is a continuation study that aims to investigate the structural features of arms and armour allegedly made of wootz, a form of pattered crucible steel first developed in ancient Southern India and already reported in the historical record around 300 BC. Since artefacts made of wootz steel were highly priced for their superior mechanical and esthetical features, expedients to recreate the typical “watered silk” surface of wootz steel soon developed. In order to discern genuine from imitations, a non-invasive analytical approached based on neutron imaging methods was applied on a set of artefacts selected by the conservation department of the Wallace Collection. Polychromatic and monochromatic imaging methods were successfully applied to determine the structural properties of the samples related to the actual manufacturing process used to obtain the surface pattern.
... NT measurements were performed at the ICON beamline of the Swiss Spallation Neutron Source at PSI (CH). The ICON station is often devoted to archaeometric analyses (Lehmann 2006;Mannes et al. 2014) through the technique of neutron imaging. In this case, the so-called Bmidi-setupŵ as used together with a 5.5 Mpixels ANDOR-NEO camera with a pixel size, when focused on the scintillator screen, of about 50 μm. ...
There is not only one methodology for the study of mineralogical phases in archaeological samples. In this paper, we discuss a strategy applied to ancient iron nail samples completely based on non-destructive analyses. The archaeological samples come from the archaeological site of Valle delle Forme (province of Brescia–Italy) and date back to the 1300–1400 ad. Neutron-based techniques, like time-of-flight neutron diffraction and neutron tomography, have been used to determine the mineralogical composition and the structure of nails. An independent check for the assessment of the presence of different mineralogical phases was given by Raman spectroscopy. The combination of different non-destructive techniques has provided very useful information on their chemical composition, nature of the patina and corrosion features of the nails (also in the bulk of the samples).
... In particular, for the non-destructive analysis of bronze metal objects, the prompt gamma activation analysis (PGAA) as a bulk composition analytical method is frequently applied [5][6][7] in combination with thin layer composition analysis methods such as X-ray Fluorescence analysis (XRF) and Particle Induced X-ray Emission (PIXE); or with Time-of-Flight Neutron Diffraction (ToF-ND) for identification of crystalline phases to study the production technology [5,7,8]. Imaging techniques (radiography and tomography) with slow neutrons, as well as with X-rays, are also non-destructive techniques well-suited to cultural heritage research [9,10]. As neutrons typically penetrate deeper into the sample and differentiate more between metals than X-rays, neutron imaging (NI) is a better choice to investigate bulky metal objects [1,11]. ...
Complementary neutron-based elemental analytical and imaging methods, i.e. position sensitive prompt gamma activation analysis and neutron tomography, were used on a bronze sculpture group of suspected South-Levantine origin. Based on the radiography and tomography images, individual figurines were chosen for elemental analysis. Selected parts were analyzed, and the bronze alloy parts were found to contain 14 mass-percent tin and 84 mass-percent copper. The non-bronze pieces contain Fe, Cl, H, Pb, S, Mn and several minor and trace constituents. This study demonstrates the synergy of the visual and compositional data when drawing conclusions about such valuable and complex metallic artifacts.
