This PDF file contains the front matter associated with SPIE Proceedings Volume 11058 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Electromagnetic waves from microwave to X-ray have been used in heritage science research filed. We have examined masterpieces of modern paintings among collections of the Ikeda Museum of 20th Century Art in Japan, by using THz time-domain imaging, near-infrared camera, and X-ray fluorescence, depending on the points to be discussed. An oil painting by Salvador Dalí has been mounted on aluminium plate for conservation purpose in the 20th century. THz imaging revealed multiple painting layers and thick supporting layers on the aluminium plate. Infrared imaging of a gouache painting by Marc Chagall clearly shows underdrawings. X-ray fluorescence method is applied to investigate paints used by Joan Miró, and successfully distinguished two white pigments.

This paper investigates the use of Optical Coherence Tomography (OCT) and Short-wave Infrared (SWIR) spectral imaging to study the deterioration of a Limoges enamel panel. Limoges enamels are formed of glass layers applied on a metal substrate and are prone to ‘glass disease’. However, the level of deterioration in Limoges enamels is generally difficult to assess visually. In this study, SWIR was used to produce a hydration level map of the enamel, which was coupled with virtual OCT cross-sections. The study shows a good correlation between levels of hydration and structural damage over the enamel panel. Hydration mapping allows visualisation of structural damage across the entire enamel in one image.

The cleaning of paintings is carried out when an artwork legibility is jeopardized. This can be due to inevitable deposits on their surface or by a modification of the varnish optical properties as a result of ageing. For the most delicate restoration cases, laser processing was widely studied as an alternative to traditional techniques of painting cleaning. It encompasses two distinct approaches: the first one involves photo-thermal disaggregation of the unwanted material with an Er:YAG laser (2.94 μm) and eventually its chemical or mechanical removal while the second one involves ultraviolet laser ablation, generally with an excimer (193, 248 or 309 nm) or a high order harmonic Nd:YAG laser (213 or 266 nm). This study proposes a comparison of these two laserbased technique for removal of an urea-aldehyde resin, Laropal A81, widely used as a binder or varnish since the 90’s, but whose interaction with a pulsed laser was never studied. For this purpose, an Er:YAG laser (El.En LightBrush2 2.94 μm 500 mJ) and a 4th harmonic Nd:YAG laser (Quantel CFR 266 nm 50 mJ) were used. The cleaning procedure was monitored in both cases by optical microscopy, spectral domain-optical coherence tomography and UV-induced fluorescence. Results showed that both sources can give satisfying results when operated in optimal conditions.

The formation and growth of metal soaps is of interest in heritage science, as soaps have been linked to a range of alteration and degradation phenomena potentially affecting works of art. However, current approaches detect metal soaps mainly in an invasive way or only at a late formation stage when the metal soaps are formed on the surface of the artwork. In contrast, Optical Coherence Tomography (OCT) has been proven to be a very suitable tool to obtain subsurface morphological information of complex multi-layered systems, such as paintings, in a non-invasive way. In this work, the capability of detecting metal soaps with an 810 nm ultra-high resolution (UHR) OCT in a selection of real and mock-up samples has been explored with OCT virtual cross-section images complemented with invasive structural and chemical analysis (SEMEDX and ATR-FTIR spectroscopy and imaging). Although the visualization of metal soaps with OCT was evident in some samples, we also show that this is not always the case. In addition, the results of this work show that extra care is needed when interpreting OCT cross-section images to avoid the risk of misinterpreting features present in the paint stratigraphy.

The industrial developments of the 19th century included the production of a variety of synthetic pigments and dyes, which were often used by artists who were not concerned with their stability over time. Among these pigments, cadmium yellow, based on cadmium sulfide (CdS), was popular with artists beginning in the mid-19th century. This pigment may discolour or darken and/or exhibit loss of adhesion and formation of white globules on the painting surface [1-2]. Its degradation involves photooxidation of CdS and the formation of degradation products (sulfates, oxalates, and carbonates) [1-4]. However, not all historic paints containing cadmium yellow degrade. It appears that CdS paints produced between the late 19th and early 20th centuries are particularly prone to degradation, as has been documented in paintings dating from 1880 to 1920 [4]. Because these paintings have been exposed to different environmental conditions, it has been speculated that the degradation of cadmium yellow may be related to imperfect syntheses, resulting in the formation of a more reactive form of CdS. However, the link between the presence of these reactive pigments and the tendency of the paint to deteriorate is not well understood. CdS is a IIb-IVa semiconductor. When excited by light of an appropriate energy, the semiconductor exhibits a characteristic near band edge (NBE) emission, closely related to the CdS energy bandgap, and emission from intra-bandgap trap states (TS) related to crystal defects [5-6]. Even though little considered when dialing with luminescent paints, the TS emission can provide useful information about surface states in nanocrystalline semiconductors [7]. Moving from nanoscience to conservation studies, the detailed investigation of TS emission in CdS paints is proposed here to probe changes in the density and energy of surface defects and ultimately in the surface reactivity of CdS following degradation. Photoluminescence imaging, microscopy, and spectroscopy – complemented by other X-ray based spectroscopies and microscopies – have been used to examine historical and modern manufactured CdS-based paints following artificial aging. Lastly we investigated the degradation of cadmium yellow paints in the painting Femme (Époque des “Demoiselles d’Avignon”) (1907) by Pablo Picasso. This study found that in degraded CdS paints the TS emission is much higher in intensity (with respect to NBE emission) and shifted to shorter wavelengths with respect to preserved paint layers. This observation indicates a higher density of TS in the degraded paint, which promotes the surface reactivity of CdS particles and the subsequent paint degradation. In general, results indicated that the analysis of TS emission is a highly sensitive method for identifying early signs of degradation in CdS paints. [1] Van der Snickt, G. et al., Anal. Chem. 2009, 81 (7): 2600–2610 [2] Mass, J. et al., Analyst 2013, 138: 6032–6043 [3] Anaf, W. et al., Dyes and Pigments 2015, 113: 409-415 [4] Monico, L. et al., Chemistry–A European Journal 2018, 24.45 [5] Cesaratto, A. et al., Analytical Methods 2014, 6.1: 130-138 [6] Rosi, F. et al., Microchem. J. 2016, 124: 856-867 [7] Krause, M. M. et al., Phys Chem Chem Phys 2015, 17:18882-18894.

Non-invasive, high resolution 3D analysis techniques are very much sought for the characterization of multilayer, multicomponent substrates, as those often encountered in artworks and objects of cultural heritage. The non-linear optical interaction of ultrashort laser pulses with a substrate is the basis of the various modalities of the non-linear optical microscopy (NLOM) techniques, recently introduced for the study of cultural heritage objects. NLOM relies on near-IR, femtosecond laser excitation of transparent or semi-transparent materials to simultaneously induce, with 3D micrometric resolution, and depending on the optical properties of the sample, multiphoton excitation fluorescence (MPEF) and second and third harmonic generation (SHG, THG) signals. MPEF emission is related to the sample chemical composition, SHG identifies the presence of non‐centrosymmetric structures and THG allows imaging interfaces between optically dissimilar materials. For paintings, it has been recently reported that valuable information about composition, layer thickness and state of conservation can be obtained by NLOM [1-3]. Although NLOM is a non-invasive technique, ensuring a correct analytical protocol requires the determination of the laser power thresholds that allow measurements under safe conditions, an aspect especially important when studying sensitive materials such as paintings. In this work, we present a novel methodology to determine the laser power thresholds for safe analyses by MPFE of painting layers. We also present the results obtained in a set of acrylic paints, extensively used by artists over the past century thanks to their properties and low cost of manufacture. To that purpose, samples were prepared as thin layers over a glass substrate and MPEF signals were induced with two different femtosecond laser sources: a Ti:Sapphire laser with wavelength of 800 nm, repetition rate of 80 MHz, and pulses of 70 femtoseconds; an optical parametric oscillator pumped by a Yb-based laser with repetition rate of 80 MHz and dual output: at 800 nm with pulses of 100 fs and at 1040 nm with pulses of 140 fs. The excitation wavelength affects the determined thresholds and the results obtained show a strong dependence on the light absorption properties and chemical composition of the painting material. [1] Oujja M., Psilodimitrakopoulos S., Carrasco E., Sanz M., Philippidis A., Selimis A., Pouli P., Filippidis G., Castillejo M. (2017) Phys. Chem. Chem. Phys. 19, 22836-22843. [2] Liang H., Mari M., Cheung C.S., Kogou S., Johnson P., Filippidis G., (2017) Opt. Express 25, 19640–19653. [3] Dal Fovo A., Oujja M., Sanz M., Martínez-Hernández A., Cañamares M.V., Castillejo M., Fontana R. (2019) Spectrochim. Acta A 208, 262-270.

Parchment was the main writing support material in the Middle Ages in Western Europe. It is made from an untanned animal skin, which is preserved by liming, scraping and drying under tension. Parchment is very sensitive to heat and water, which causes in extreme case the denaturation of collagen, its main constituent, to gelatin. The measurement of the shrinkage temperature, by differential scanning calorimetry (DSC) or the micro-hot table (MHT) method, is commonly used in the cultural heritage field to assess the degradation state of collagen-based materials. However, these techniques are invasive, as they require a sample, and destructive, which is an issue in the case of some historical artifacts. The aim of this work is to demonstrate the potential of nonlinear optical (NLO) microscopy to investigate in a non-invasive and quantitative way the conservation state of historical parchments. NLO microscopy enables three-dimensional (3D) imaging with micrometer-scale resolution based on an intrinsic optical sectioning. A key advantage is its multimodal capability. Two-photon excited fluorescence (2PEF) signals are emitted by a wide range of materials (fluorophores) in historical artifacts with specific absorption and emission fluorescence spectra [1]. SHG signals are specific for dense and well aligned structures such as fibrillar collagen, and vanish for centrosymmetric materials such a gelatin. Accordingly, SHG microscopy provides structural information about the 3D organization of the fibrillar collagen within parchments and other skin-based artefacts [2,3]. Notably, it enables in situ non-invasive assessment of parchment degradation, which is characterized by the loss of the SHG signal and the onset of a 2PEF signal [2]. In order to quantify intermediate states of degradation, we further implement polarization-resolved SHG (P-SHG) microscopy: the SHG intensity is recorded as a function of the linear polarization orientation of the excitation for each pixel of the image. P-SHG microscopy provides two quantitative information: the main orientation and the degree of orientation disorder at the submicrometer scale (Figure 1). P-SHG images are acquired in a set of modern parchments that were artificially degraded by exposure to dry heat for increasing duration. The degradation state of the collagen in these parchments is assessed using DSC. P-SHG data are in good agreement with DSC measurements and prove to be a complementary investigation tool that requires no sampling. Most importantly, P-SHG is shown to reveal the earliest states of degradation. At the end the 2nd World War, Chartres’ library was partially destroyed. The manuscripts were exposed to fire and then water. The degradation states of the manuscripts are heterogeneous (Figure 2). P-SHG microscopy was performed on these manuscripts to determine their conservation states. Moreover, these analysis were also performed in restored and unrestored parchments and show that the performed restoration did not alter the conservation state of the fibrillar collagen within the parchment. All these results show the high potential of NLO microscopy for in situ quantitative measurements of the conservation state of historical parchments. Moreover, this methodology could be extended to other cultural heritage materials. References [1] G. Latour et al., Opt. Express 20, 24623 (2012) [2] G. Latour et al., Sci. Rep. 6, 36344 (2016). [3] L. Robinet et al., ICOM-CC 18th Triennial Conference Preprints, art. 1609 (2017).

Ancient Chinese glazes are colorful and mysterious, but it has been puzzling for the researchers to illustrate the coloring mechanism of glaze scientifically and characterize glaze colors specifically. In this study, the macro-spectrum measurement system and spectral measurement specification of ancient ceramics are built up. The location and distribution of the color of the specimens of each kiln are marked on the color chart. A quantitative optical evaluation method is established for the description of the color and texture of the ancient ceramic glaze. The color and texture of ancient glaze is determined by its chemical composition and microstructure. Factors affecting glaze color include chemical factor and physical factor. Fe2+/Fe3+ ions determine the color of transparent glaze, and the body color beneath the transparent glaze also modify the visual effect of the porcelain. While the coloring mechanism of opaque and translucent glaze is more complicated. The study shows that, the mild blue colors of Jun glaze and Ru glaze mainly result from the amorphous photonic structures in the glazes, which is an important breakthrough in understanding the coloring mechanism of ancient Chinese glazes. Computer simulation of glaze structure and simulative calculation of optical properties is carried out to establish the corresponding relationship between structure and reflective spectrum. Coloring mechanism for the glazes from the same kiln site, however, is not invariable, highly related with glaze composition and firing conditions. Both ion coloring and phase-separation structure take effects in the coloration of the famous Ru glaze. Fe acts as both flux and coloring element, favors the strong immiscibility tendency between SiO2 and CaO, and precipitates from the glaze under supersaturation. The analysis reveals that ‘oil spot’ patterns of the Jian bowl of the Song Dynasty contain large quantities of highly pure epsilon-phase iron oxide. It also has a special 2D intricate microstructure with interesting optical properties, which are responsible for the remarkable silvery look of the ‘Oil spots.’ Using plant ash as the main raw material, composite decorative glazes and high-iron crystallization glazes are designed and prepared. In imitation of the droplet phase-separation structure of the ancient Qionglai and Jun glazes, a photonic structure of tightly-piled micro-balls is prepared, which provides a solid scientific basis for the physical color mechanism of the ancient ceramic glaze. The spectral database of ancient Chinese glazes can also provide important reference for the non-destructive classification and authentication of ancient ceramics from different kilns.

We propose and experimentally validate a new hyperspectral camera based on the Fourier-transform approach. Two delayed replicas of the optical field entering an imaging system are produced by the Translating-Wedge-Based Identical Pulses eNcoding System (TWINS).¹ This device is a common-path birefringent interferometer that combines compactness, high delay precision, long-term stability and insensitivity to vibrations. The TWINS scans the phase delay between the two replicates along many optical cycles. The replicas produce, upon recombination, a high contrast interferogram in each pixel of the detector. An appropriate Fourier transformation of the dataset produces spectrally resolved images that exhibit high contrast and spatial resolution only limited by the lens and the sensor. The main features of the system in terms of spectral resolution, contrast and bandwidth will be presented. Examples of application in conservation science will be also reported.

The use of non-invasive hyperspectral imaging techniques has become standard practice in the materials analysis and study of precious cultural heritage objects such as drawings, paintings, murals and more. However, the non-linear mixing of spectral signatures from complex and heterogenous objects with multiple colorants present below the resolution limits of the camera can complicate material identification. Consequently, ground truth measurements are still usually obtained from microscopic samples removed and embedded to expose stratigraphy and obtain sub-surface information about the artist’s material choices and technique. This work considers a microscopic spectral imaging technique capable of mapping molecular information in such micro samples at high spatial and spectral resolution while avoiding some of the challenges of complimentary techniques, such as swamping fluorescence in Raman spectroscopy or long integration times using FT-IR spectroscopy. Construction of a dark field hyperspectral microscope for cultural heritage samples is described using a tunable light source to illuminate the sample monochromatically from the visible to near infrared wavelengths, with the diffusely reflected light collected from the specimen with a long working distance, 20x objective. The illumination and detection arms were decoupled to better focus the power of the tunable light source across the tunable range through Köhler illumination optics. By mounting the optical train on a rotating arm, we can achieve multiple angles of illumination and optimize lighting conditions. The sample is also rotated in order to reconstruct an even distribution of light across the field of view. This multi-axis movement capability also provides exciting opportunities to leverage more than simple spectral information from an image series such as surface topography and differential phase contrast information. The developed microscope was used create a library of spectral signatures for comparison to painting cross sections, and the ability of the microscope to identify and examine individual pigment particles was tested.

UV-Vis fluorescence spectroscopy is a convenient non-invasive tool to study polychrome historical objects. It can help to identify the nature of certain materials when they present specific fluorescent properties. However, given the complexity of such stratified and heterogeneous materials, the attribution of the detected fluorescence to a specific constituent (e.g. a pigment or a binder composing a paint layer) is not straight forward. Moreover, the experimental data need to be corrected for a number of effects that can influence the recorded spectral distribution. The application of the self-absorption correction procedure (that require the simultaneous recording of reflectance profiles) [1,2] to experimental fluorescence data gathered on the polychromatic surface of the Codex Borbonicus, a 16th century Aztec manuscript, is described. The results are confronted to a different methodology [3] that is based on the hypothesis of transparent non-scattering paint layers. This second approach allows to establish more clearly the material origin of the detected emission and to discriminate apparent fluorescence (emitted by the substrate and transmitted through the paint layers) from intrinsic emission generated by the coloring materials under study. As a matter of fact, most of the various emission profiles measured in the paint layers of the studied manuscript actually originate from the substrate, and should not be used to characterize the coloring materials. This study demonstrates how carefully fluorescence spectroscopic and imaging data recorded on complex and stratified materials should be interpreted. [1] C. Clementi, C. Miliani, G. Verri, S. Sotiropoulou, A. Romani, B.G. Brunetti, a Sgamellotti, Application of the Kubelka-Munk correction for self-absorption of fluorescence emission in carmine lake paint layers., Appl. Spectrosc. 63 (2009) 1323–30. doi:10.1366/000370209790109058. [2] G. Verri, C. Clementi, D. Comelli, S. Cather, F. Piqué, Correction of ultraviolet-induced fluorescence spectra for the examination of polychromy., Appl. Spectrosc. 62 (2008) 1295–302. doi:10.1366/000370208786822296. [3] F. Pottier, A. Michelin, C. Andraud, F. Goubard, B. Lavédrine, Characterizing the Intrinsic Fluorescence Properties of Historical Painting Materials: The Case Study of a Sixteenth-Century Mesoamerican Manuscript, Appl. Spectrosc. 72 (2018) 573–583. doi:10.1177/0003702817747276.

Pigment identification and mapping gives us insight into an artists' material use, allows us to measure slow chemical changes in painted surfaces, and allows us to detect anachronistic uses of materials that can be associated with either forgeries or past restorations. Earlier work has demonstrated the potential of a dictionary-based reflectance approach for pigment classification. This technique identifies pigments by searching for the pigment combinations that best reproduce the measured reflectance curve. The prospect of pigment classification through modeling is attractive because it can be extended to a layered medium -- potentially opening a route to a depth-resolved pigment classification method. In this work, we investigate a layered pigment classification technique with a fused deep learning and optimization-based Kubelka-Munk framework. First, we discuss the efficacy of the algorithm in a thick, single-layer system. Specifically, we consider the impacts of layer thickness, total pigment concentration, and spectrally similar pigment combinations. Following a thorough discussion of the single layer problem, the system is generalized to multiple layers. Finally, as a concrete example, we use the two-layered system to demonstrate both the impacts of layer thickness and dictionary content on paint localization within the painting. Results of the algorithm are then shown for mock-up paintings for which the ground truth is known.

Among metal alloys, bronze has been used for millennia to produce many kind of objects, from decorative and religious pieces to sculptures. Although many bronze objects have been well preserved to this day, copper and bronze can be affected by severe degradation involving the formation of copper chloride products, known as “bronze disease” [1]. These chloride products are considered responsible for the rapid decay of bronze, which can ultimately cause the loss of unique and historical artworks. However, copper chlorides constitute only a small fraction of the vast and complex class of corrosion products which can form on historical bronze and copper. It is essential to be able to differentiate between stable from more dangerous unstable corrosion products. A major challenge of bronze conservation is to non-invasively identify the unstable chloride corrosion throughout the whole artefact. This information is critical for decision-making in conservation process. Different analytical approaches are available to identify these corrosion products. However, most conventional methods require sampling which is not only destructive, but also usually unrepresentative of the object as a whole. Spectral imaging constitutes a class of non-invasive techniques which have been largely used for the identification and mapping of pigments in paintings [2]. However, it is more challenging to apply spectral imaging to 3D objects. We have developed a hyperspectral imaging set-up in the visible and near infrared spectral range for 3D objects to rapidly identify and map the corrosion products non-invasively [3]. A preliminary application has been done to study ancient bronze artworks from the National Museum of China. These results are further supported by analysis carried out on selected samples of the same collection with Fibre Optic Reflectance Spectroscopy, Attenuated Total Reflection (ATR)-FTIR spectroscopy, X-rays diffraction, Raman spectroscopy and SEM-EDX. The possibility of successfully performing hyperspectral imaging for the study of corrosion products would represent a completely novel approach in the analysis of ancient bronze and copper objects. [1] Scott, A. D. A Review of Copper Chlorides and Related Salts in Bronze Corrosion and as Painting Pigments. Studies in Conservation, 45: 39-53 (2000) [2] Liang, H. Advances in multispectral and hyperspectral imaging for archaeology and art conservation. Applied Physics A, 106 (2), 309-323 (2012) [3] Liang, H. et al. Remote hyperspectral imaging with simultaneous 3D texture mapping. Optics for Arts, Architecture, and Archaeology, 10331-25 (2017)

This manuscript gives an overview of the multipoint method and the development of an easy to use measurement system which measures the deformation of large buildings. The multipoint method has previously been tested1, 2 and used mainly under controlled laboratory conditions (e.g. indoors). Difficulties are introduced when this method is used outdoors, mainly because of the increased measurement scale and the uncontrolled environment. Differences in air pressure due to convection or wind, as well as fog or rain can cause severe perturbations to the light which propagates towards the sensors. Compared with existing systems, such as laser trackers, our system does not need to scan the building, which leads to much higher temporal resolution, which in turn can be used to achieve a reduced statistical measurement uncertainty (averaging in time).

The study and analysis of defects in wall paintings is possible by stimulated infrared thermography, this approach is of great interest to the scientific community responsible for the conservation and restoration of these works of art. The work presented consists in identifying the best way to stimulate and analyze the thermal signals measured on these works of art in order to reveal defects invisible to the naked eye such as internal decohesions. In the case of wall paintings, for example, optical effects associated with the presence of a pictorial layer can degrade this detection. To do this, we compared two excitation modes of an academic sample, excitation using conventional halogen sources emitting in the visible and near infrared and an excitation source emitting in the mid-infrared. We compared the two excitation modes and applied a postprocessing to these two experimental approaches: SVD. The results presented made it possible to observe the interest of infrared sources and the additional contribution made by post-processing of the SVD type.

Ancient wall mosaic decorations can be exposed to uncontrolled environmental conditions. The main mosaic conservation problems, induced by external factors, are related to temperature and humidity variations, which may result in moisture, salt crystallization and accelerated material deterioration within the underlying layers. Though such deterioration in the subsurface is not immediately visible, it can strongly affect the preservation of the entire structure and the decoration layer in the short or long-term future. In this paper, we present and discuss laboratory experimental results of Digital Holographic Speckle Pattern Interferometry (DHSPI), applied to the subsurface diagnostic of a mosaic model after artificially induced thermal change and under simulated environmental conditions in climate chamber. The tests were performed on a custom-built wall mosaic model with known construction and known defects, which are simulating voids, detachments and deteriorated, restored or reshuffled areas. Two types of induced stress were used: 1) low thermal excitation emitted by IR lamps directly to the surface; 2) simulated environmental conditions inside the climate chamber. In regards of the in-situ diagnostic investigation any structural alteration occurs as a natural reaction to the surrounding environment and monitoring of surface reactions and defect detection under natural fluctuations it could be considered as a very important aspect of implementation to optimize range of applicability for non-destructive remote portable instrumentation. The obtained DHSPI results on the detection of known defects in the mosaic under artificially induced thermal alteration and under simulated environmental conditions are compared and discussed.

X-ray imaging is one of the oldest technic used in art analysis. X-Radiography is now completed with tomography. Used on bronze sculptures, it gives unrivalled information on state of conservation or fabrication process. The treasure of Bavay, discovered in 1969 in the north of France, is a hoard constituted by 371 bronze objects dated from the 1st to 3rd century AD. Among objects of very diverse shape and function, an exceptional set of Roman statuettes was discovered. Two Mercury statuettes were studied and, apart that they are hollow, their characteristics are very different. The metal walls are thin and even for the Lysippean Mercury and could only be done by the indirect lost wax casting process. On other hand, Indigenous Mercury still own its inner refractory core made of clay, whose shape is a very simple evocation of the statue. Here the direct lost-wax process was used, with first the core shaping, on which wax was directly carved. In some cases, spatial information is difficult to read on flat 2D radiographies, so complementary images are made thanks to 3D tomography. Reconstruction algorithms generate a 3D object issued from 720X-Ray images, showing the internal and the external surfaces. Virtual cutting can show any part of the object, allowing a detailed visualization of the inner parts. For example, Jupiter statue in tomography showed on the inner surfaces metal infiltration and a secondary casting of a lead-tin. Other analysis can be added to tomographic model: the surface 3D acquired with a scanner can add more precision on external surface representation: it was made for the Jupiter statue. In some cases also, photography for surface color analysis, or X-ray fluorescence chemical maps could also be placed on 3D models for a better materials localization.

The brief overview of most important case studies concerned with use of laser techniques for documentation, replication and reconstruction of out-door sculptural monuments in St.Petersburg city is presented. Use of 3D laser scanning in combination with computer modelling and use of CNC milling machines and additive technologies open new perspective in Cultural Heritage preservation.

Accurate measurements of the geometric shape and the internal structure of cultural artifacts are of great importance for the analysis and understanding of artworks such as paintings. Often their complex layers, delicate materials, high value and uniqueness preclude all but the sparsest sample-based measurements (microtomy or embedding of small chips of paint). In the last decade, optical coherence tomography (OCT) has enabled dense point-wise measurements of layered surfaces to create 3D images with axial resolutions at micron scales. Commercial OCT systems at biologically-useful wavelengths (900 nm to 1.3 μm) can reveal some painting layers, strong scattering and absorption at these wavelengths severely limits the penetration depth. While Fourierdomain methods increase measurement speed and eliminate moving parts, they also reduce signal-to-noise ratios and increase equipment costs. In this paper, we present an improved lower-cost time-domain OCT (TD-OCT) system for deeper, high-resolution 3D imaging of painting layers. Assembled entirely from recently-available commercially-made parts, its 2x2 fused fiber-optic coupler forms an interferometer without a delicate, manuallyaligned beam-splitter, its low-cost broadband Q-switched super-continuum laser source supplies 20 KHz 0.4-2.4 μm coherent pulses that penetrate deeply into the sample matrix, and its single low-cost InGaAs amplified photodetector replaces the sensitive spectroscopic camera required by Fourier domain OCT (FD-OCT) systems. Our fiber and filter choices operate at 2.0±0.2 μm wavelengths, as these may later help us characterize scattering and absorption characteristics, and yield axial resolution of about 4.85 μm, surprisingly close to the theoretical maximum of 4.41 μm. We show that despite the moving parts that make TD-OCT measurements more timeconsuming, replacing the spectroscopic camera required by FD-OCT with a single-pixel detector offers strong advantages. This detector measures interference power at all wavelengths simultaneously, but at a single depth, enabling the system to reach its axial resolution limits by simply using more time to acquire more samples per Ascan. We characterize the system performance using material samples that match real works of art. Our system provides an economical and practical way to improve 3D imaging performance for cultural heritage applications in terms of penetration, resolution, and dynamic range.

Novel types of supercontinuum sources radiating in the infrared (IR) spectral region provide ultra-broadband spectral coverage and maintain distinctive laser-like properties of emission such as brightness, spatial coherence and high power. Being a perfectly suitable light source for mid-infrared optical coherence tomography (OCT) and spectroscopy, supercontinuum sources initiated a significant amount of recent developments in these fields and promise to be a gamechanging factor in the nearest future. In this paper, we exhibit a simple, optimized and relatively cost-effective system operating in near and mid-infrared ranges and combining OCT and co-registered IR spectroscopy. The performance of the OCT modality of the setup is evaluated with respect to the sensitivity and roll-off. Due to reduced scattering inherited with the new spectral window, we achieve the enhancement in the penetration depth in artificial paintings, ceramics and pottery. Furthermore, the hyperspectral data is used to supplement structural information and access to the chemical composition of the sample. The gained results reveal the potential of the multimodal system for non-destructive testing, art and cultural objects diagnosis.

Typically, varnish coatings were applied to Old Master paintings to improve their visual appearance, saturating the colours. However, over time, varnishes deteriorate and discolour, obscuring or altering the appearance of the artwork, necessitating their removal (usually through the use of a solvent) and replacement. Varnish removal presents a degree of risk to the paint surface and may result in loss of original materials or other damage. Thus, diagnostic methods that can support conservators during varnish removal are very valuable. Optical Coherence Tomography (OCT), a white light interferometry technique based on the Michelson interferometer, has been proposed as an ideal tool for monitoring the cleaning and treatment of artworks and historical objects. This is owing to its ability to provide non-invasive and accurate measurements across the entire surface of an artwork of the stratigraphy of transparent and turbid multi-layered structures. In many cases, however, difficulties may arise when attempting to distinguish degraded glaze layers on paintings (coloured, translucent layers containing pigments with refractive indices very close to the binding medium) from layers of aged varnish due to similarities in their appearance and scattering properties in OCT scans. In order to mitigate the possibility of damage through the accidental removal of glaze layers, we propose a simple and entirely non-invasive technique to identify the spectral features of a semi-transparent layer using a combination of OCT and spectral imaging in the visible range. Building on preliminary studies 1,2, the technique utilises an algorithm to automatically obtain the thickness distribution of the surface layers from the OCT volume of a region with relatively uniform pigmentation and colour. This information is then coupled with the spectral data from the same region to derive the spectral characteristics of each translucent surface layer. Such characteristics may then be used to the discriminate between aged varnishes and glaze layers. The potential of this approach has been demonstrated on mock-up samples and paintings from the National Gallery in London. [1] Lange, R., Liang, H., Howard, H. and Spooner, J., “Optical coherence tomography and spectral imaging of a wall painting,” SPIE Newsroom (2011). [2] Liang, H., Lange, R., Howard, H. and Spooner, J., “Non-invasive investigations of a wall painting using optical coherence tomography and hyperspectral imaging,” Proc. SPIE 8084, 80840F (2011).

The analysis of painting materials and techniques provides important information to history and archaeology research, as well as to scientists and conservators involved in the conservation of objects of cultural heritage. However, the examination of statistically significant number of objects is required to understand the material use typical of a class of objects (e.g. paintings from a certain geographic region, in a certain period, for a certain purpose). This necessitates efficient data collection and the development of methods for their effective analysis. The spectral imaging system developed in our group, PRISMS, enables automated high resolution spectral imaging in the visible/near infrared regime of paintings of any size. The automatic clustering of the spectral reflectance data at the pixel-level can be used for the initial classification of the areas according to their reflectance spectra. In this study, a new clustering algorithm, based on self-organised mapping (SOM), for the sequential automatic analysis of large spectral datasets is presented. The development of such methods makes the analytical procedure more efficient by reducing the number of areas that need to be further examined based on their unique reflectance spectra. The preliminary clustering of the spectral imaging data is supported by the high-resolution x-ray fluorescence (XRF) maps. The multimodal spectral characterisation of the painting materials is completed with the application of high spectral resolution Fibre Optic Reflectance Spectroscopy (FORS) and Raman spectroscopy on each cluster area. Optical coherence tomography (OCT) is used to examine the 3D microstructure of the substrates as well as the painting technique through the examination of the stratigraphy. Examples based on data from collections of Peruvian paintings on paper substrate, Chinese export paintings and Peruvian paintings made in the style of Chinese export painting will be presented.

Macroscopic mapping and hyperspectral imaging in the mid-infrared region (2500-25000 nm/4000-400 cm^-1) are promising technologies in the field of analysis of cultural heritage. So far they have been successfully employed to study paintings and illuminated manuscripts, gathering important information on spatial distribution of artists’ materials. The present paper reports on the application of mid-infrared macroscopic mapping and hyperspectral imaging to the study of artworks. For an exhaustive overview, instrumental details, working principles and image processing methods will be also presented and discussed.

Scanning macro‐X‐ray fluorescence (XRF) spectroscopy on works of art provides researchers with rich data sets containing information about material composition and technique of material use in a compelling visual format in the form of element‐specific distribution maps. The accuracy of these maps, however, is influenced by the topography of the object, which ideally is two dimensional, relatively flat and able to be placed parallel to the data collection x-ray optics. In reality, few works of art are truly flat. Small nuances in the visualized elemental intensity may be introduced into element distribution maps by the presence of topography, whether the curve of a centuries-old panel painting, the natural warping of works on paper or parchment, or, in the most extreme cases, in actual three dimensional objects. The inability to confidently ascribe a change in signal intensity to actual elemental composition versus topographically-induced variance, therefore, presents a challenge, particularly when attempting to identify markers of artists’ techniques, compare several objects, or overlay/register images from scanning XRF with those from other imaging modalities. To address this challenge, this paper introduces a new methodology for post-processing scanning XRF data sets to correct for elemental intensity variations as a function of topography. The method augments the acquired XRF data based on a three-dimensional reconstruction of an object and a set of elemental intensity/distance response functions. These response functions act as a calibrated guide for modifying the intensity map based on depth variation. The geometry-based parameters of local surface shape (curvature), distance of the XRF detector from the surface, region of intersection of the incident fluorescence beam with the surface, and the orientation of the incident beam with respect to the surface normal, are each accounted for in the calibration phase as a large set of pre-acquired examples. This provides a mechanism for capturing and understanding the anticipated variations in the macro-XRF data, interpolating the examples in order to smoothly estimate variations, and applying those variations as corrections to macro-XRF data collected on non-planar surfaces. The acquisition and representation of the macro-XRF variation as a function of the geometry is explained, with an emphasis on understanding the parameters that induce the most severe errors in the XRF estimates. The representational framework for collecting, storing, and summarizing calibration data over a large number of scans is discussed, followed by several proof of concept examples, including data from one of the masterpieces of the J. Paul Getty Museum collection: Mummy portrait of a woman (JPGM #81.AP.42), also known as Isidora. This 1st century Romano-Egyptian funeral portrait on wood was originally included in mummy wrappings, and is therefore curved to match the natural curves of the embalmed subject. An XRF scan of Isidora was recently undertaken as part of a long-standing project – Ancient Panel Paintings: Examination, Analysis, and Research (APPEAR) – that seeks to increase our knowledge on the materials and manufacture of paintings of this type. The natural curvature of this panel painting, together with the rich texture typical of the encaustic technique, makes Isidora the perfect candidate to test the proposed methodology.

Material analysis is important to the study of architectural interiors and wall paintings in order to inform the research in history and to monitor the state of conservation. Multimodal spectral analysis is increasingly used in mobile lab campaigns conducted in situ at historical sites. Some challenges specific to the investigation of immovable cultural heritage arise from the inaccessible heights and remoteness of the sites. Therefore, complementary spectroscopic techniques that can be conducted from the ground at a large distance (> 3 m) are required. The Imaging and Sensing for Archaeology, Art history and Conservation (ISAAC) Mobile Lab routinely employs remote spectral imaging to record the spectral reflectance in the visible and near infrared of wall paintings at high spatial resolution per pixel. Raman spectroscopy identifies molecular structural fingerprints by observing the spectral shift from the excitation laser wavelength resulting from molecular vibrations. A by-product of Raman spectroscopy is laser induced fluorescence spectroscopy (LIF). Laser-induced breakdown spectroscopy (LIBS) detects characteristic lines for different elements from the plasma created by high power laser pulses. The combination of Raman, LIF, LIBS and spectral reflectance can provide complementary material information about the artworks: molecular structure and elemental composition. Assisted with a computer-controlled telescope mount, small area remote spectroscopic mapping (2D scanning) with Raman and LIF is also achieved to complement long range remote visible and near infrared spectral imaging. In this work, we present the developments of a combined long range mobile remote spectroscopy system for working in the range from 3m to 15m, and its recent applications in remote material identifications on wall paintings.

A mid-infrared spectroscopic imager needs to be portable and tough for the identification of dyestuffs used for murals in ancient tombs during archaeological on-site analysis. Meanwhile, an extremely compact and tough hyperspectral camera with mass less than 2 kg is required for mounting on drones to observe nutritive components like nitrogen and phosphorus. We proposed a near-common-path wavefront-division phase-shift interferometer as an imaging-type twodimensional Fourier spectrometer. Because the proposed interferometer has strong robustness against mechanical vibrations, a palm-sized Fourier spectroscopic imager can be realized without an anti-mechanical vibration system. We developed a palm-sized (80-mm cube weighing 0.5 kg) and tough hyperspectral camera for mid-infrared light (wavelength of 8–14 μm) that can be operated using only a notebook personal computer. Furthermore, the field of view of a conventional hyperspectral camera is narrow (e.g., 6.4 deg × 5.1 deg). However, employing a proposed field angle correlation method and using a fisheye lens as the objective lens, the field of view can be expanded to 180 deg. The total price of the mid-infrared two-dimensional spectroscopic imager is no more than several thousand USD because a lowprice microbolometer (Vision Sensing, VIM-80G2, wavelength range: 8-14 μm, 80 × 80 pixels, price: 300 USD) is used. Additionally, a long-stroke (10 mm) and high-resolution (Optical encoder resolution: 100 nm) impact-drive actuator (Technohands XCWT70-10 weighing 30 g) is introduced as a low-price (1000 USD) and tough phase-shift stage with cross-roller linear-motion guides.

This paper investigates optical coherence tomography (OCT) as an advanced, non-invasive method for 2D and 3D imaging of the surface and subsurface morphology of glass cultural heritage. The OCT system used is a commercial ThorLabs Ganymede II spectral domain-Fourier domain system with a 930 nm center wavelength, axial resolution of 4-6 μm, and lateral resolution of 8 μm. Results from model alkali silicate glass artificially aged at 90°C and 90% RH allow distinction of real features from artifacts produced by the highly reflective glass, and serve as a basis for interpretation of deterioration phenomena. Analytical results from historical glass artifacts are focused on a group of musical glass flutes created in Paris by Claude Laurent between 1807 and 1848. OCT images are compared to results of destructive analysis of the same samples and objects by scanning electron microscopy with backscattered electron imaging of cross-sections, as well as non-invasive light microscopy and NIR fiber optic reflectance spectrometry, the latter of which yields complementary molecular information in terms of water vibrations in hydrated glass.

With its intrinsic preciousness, symbolic, and aesthetic connotations, gold leaf was essential to the decoration of artworks from antiquity to the Renaissance. Despite this importance, the physical characteristics and chemical composition of gold leaf in works of art have not, to date, been extensively studied. In this work, case studies from a number of works of art demonstrate the ability of scanning macro X-ray fluorescence (MA-XRF) spectroscopy for in situ, non-invasive examination of the physical characteristics and the elemental composition of historic gold leaf in works of art in different media. Macro-XRF scanning has opened up new avenues of research by providing insight into how these micron-thin sheets of gold were manipulated and applied in individual objects [1,2]. Besides elemental composition, data provided by MA-XRF on gilded objects includes the visualization of the shape, size, and application techniques of individual gold leaves. For example, measurements of the dimensions of individual gold leaves obtained directly from XRF map data of thirteen 14th and 15th century Italian panel paintings reveals differences in the dimensions of gold leaf across different administrative regions throughout the Italian peninsula during this period. This work suggests a deterministic system of leaf production, which varied between the city-states, controlled by the different city guilds. In addition to leaf dimensions, a comparison of the degree to which gold leaves were overlapped during the gilding process reveals important clues about the artistic hand of individual artists. Overlap measurements appear consistent between artworks ascribed to the same artists, even when that artist is gilding with gold leaf of different dimensions, but differ between artworks painted by different artists. Taken together, these measurements advance art historical scholarship by providing a material understanding of artistic practice. In addition to elucidating several facets of the original artistic creative process, XRF maps have also helped identify subsequent interventions, providing new evidence of possible historic conservation or restoration efforts. Our knowledge of how gold leaf was manufactured is based on historical treatises rather than material analysis. The ability to confidently detect variations in minor and trace elements in historical gold leaf may provide new tools to better understand dating, location of production, and trades. The suitability and inherent limitations of MA-XRF for the semi-quantitative analysis of the gold leaves, based on a feasibility study using a set of modern gold leaf samples will also be discussed. A ground truth for the concentrations of these, and other trace, elements was validated using inductively coupled plasma-mass spectrometry (ICP-MS). Linear regressions for gold, silver, and copper provide a model for relating XRF intensity to concentration that can be tested on the XRF map data obtained from the historic artworks. [1] D. MacLennan, L. Llewellyn, J.K. Delaney, C. Schmidt Patterson, Y. Szafran, K. Trentelman, “Visualizing and measuring gold leaf in 14th and 15th century Italian gold ground paintings using scanning macro X-ray fluorescence spectroscopy (MA-XRF),” Heritage Science, Submitted (2019). [2] D. MacLennan, L. Llewellyn, “Visualizing and measuring gold leaf: Case Study: Gentile da Fabriano,” The Burlington Magazine, Submitted (2019).

In our paper we will present results of an on-going project connected with monitoring the condition of 12 fragments of the Museum of King Jan III’s Palace at Wilanów (Warsaw, Poland) building façade by 3D structured-light scanning method. During 30 months, 7 series of three-dimensional measurements have been planned. In each of the twelve elevation fragments, chosen by the conservation and architecture departments as particularly interesting, an area of 120 mm x 120 mm was scanned with 2500 points/mm² resolution. This article describes the methodology of the measurement process, the hardware setup developed especially for this purpose, as well as the data processing path and analysis algorithms. In addition to having such accurate measurement data, we must still be able to match the measurements carried out in the same place at intervals of several months. For this purpose the areas of interest were marked with special aluminum targets, embedded with three intersecting planes. The algorithm of their detection, analysis and use for aligning data from subsequent measurement series is discussed. A portable SLS 3D-measurement head with two cameras, integrated with linear drive has been developed for scanning purposes and adopted to use in outdoor condition. The 3D scanner has a measurement volume limited to 45 mm x 50 mm x 10 mm for a single scan, due to high-resolution requirements. In less than 25 minutes, 40 measurements are acquired at various positions, covering the entire area, with the support of a controlled linear stage stand. Individual scans are pre-aligned with limited accuracy and then fitted using the Iterative Closest Point algorithm. The final representation of each fragment is a cloud of points with color containing more than 200 million 3D measurement points. We present the results of 3D measurements and a proposition of a monitoring procedure for assessing the change in 3D surfaces over time.

Changes of temperature and relative humidity of the environment where the artefact is stored can cause deformations of the surface that can harm the object or affect the repeatability of the measurement. Currently, there are very few techniques and approaches that allow studying non-invasively the surface deformations of objects of different sizes maintaining accuracy of the order of micrometres. To address this problem, three different systems based on a conoscopic holography sensors have been tested on hygroscopic samples. Moreover, we implemented a low-cost apparatus for controlling relative humidity. Eventually, we investigated procedures that use reference standards, insensitive to thermal and hygrometric variations with the scope to assess short and long-term drifts of the instrumental set-up. We tested the approach on samples of paper and lambskin parchment and on a wooden icon.

Reflectance Transformation Imaging is a technique that provides a digital and useful representation of an object through photometric and geometric local assessment of the surface. RTI technique consists in acquiring a sequence of images from a fixed observation position while varying the direction of the light source around the observed object. Thanks to a further reconstruction process, the continuous angular reflectance for each pixel can be computed from the set of discrete acquisitions and rendered interactively. Currently, the most used mathematical functions that allow this reconstruction from RTI’s acquisitions are Polynomial Texture Mapping (PTM), a method based on Hemispherical Harmonics (HSH) and most recently the Discrete Modal Decomposition (DMD). For these three approaches, a uniform spatial distribution of light sources is an implicit hypothesis. In practice, it is often not possible to achieve this uniform spatial distribution due to intrinsic limitations in systems or in the acquisition conditions. It is then necessary to take into account this nonuniformity in order to avoid artifacts that could alter modelling and subsequent visual rendering. To address this issue, we propose a methodology consisting in the estimation of the local density of the lighting directions used during RTI acquisition. These values are then used to generate a weight for each light position enabling to correct its contribution in the regression performed during the fitting.

The château de Selles (dating back to the 14th century) in Cambrai is one of the most important monuments in France for medieval graffiti. Today the some parts of the engraved walls are endangered by a complicated weathering process. The present project lead by archaeologists in collaboration with universities and companies which are specialized in 3D surface scanning and 3D modelling aims to apply archaeological methods and new optic technologies in order to preserve the endangered engravings and to study the graffiti. For documentation, color photography (fontal and side light) is used for the survey, archive and deciphering by tracings of the engravings. 3D high resolution scanning of the engraved parts of the walls have been used to get a digital print of most of the traces on the wall in order to be able to work on the 3D models. The 3D models of the engraved are used by archaeologists and paleographers to explore precisely the engravings and decipher objectively the motif and texts. The repeated 3D scanning of some parts of the castle have led to a 6 year monitoring of the weathering processes. A complete photogrammetric survey was made on the outside and inside of the castle in order to build up a virtual visit to the castle thanks to a virtual reality headset that helps the visitor to discover the engravings in an immersive experience.

Precise and robust 3D model reconstruction is required in various outdoor scenarios such as aircraft inspection, rapid prototyping, and documentation of an archaeological site. This paper is focused on the development of a mobile structured light 3D scanner for online reconstruction. We use a structured light projection for fast data acquisition. We use deep learning based pattern matching to improve accuracy up to 0.1 pixels. Our FringeMatchNet is based on the U-Net architecture. The network produces an estimated shift heatmap with subpixel accuracy. Each pixel (x, y) of the heatmap represents the probability that the shift between the two image patches is equal to (x, y). We generated a large dataset that combines synthetic and real image patches to train our FringeMatchNet. We compare the accuracy of our FringeMatchNet with other stereo matching algorithms both hand-crafted (SGM, LSM) and modern deep learning-based. The evaluation proves that our network outperforms hand-crafted methods and competes with modern state-of-the-art deep learning based algorithms. Our scanner provides the measuring volume of 400 × 300 × 200 mm for an object distance of 600–700 mm. It combines portability with an object point resolution between 0.2 and 0.1 mm. We made our FringeMatchNet and the training dataset publicly available. Deep learning-based stereo matching using our FringeMatchNet facilitates subpixel registration and allows our scanner to achieve sub-millimeter accuracy in the object space.

A large amount of iron and steel artifacts produced in the central European area between 2nd and 14th Centuries is constituted by pattern welded iron-phosphoric iron and steel components. Phosphoric iron is a substitutional alloy, which is obtained by using iron ore from swamps in which decomposition of dead organisms enriches the iron rich soil with phosphorous. The identification of phosphoric iron alloy in ancient artifacts is important for determining their place of origin, production procedure and technological characteristics. A well-established technique for investigating the bulk structure of ancient metallographic artifacts is neutron tomography, using cold neutrons. It provides image-data capable of enhancing differences between phosphorous rich iron and the standard iron areas. However, neutron imaging is costly and complex to implement. Therefore, the exploration of new techniques capable of providing additional data on the nature of alloys would be highly needed. A pilot study addressed to test the applicability of reflectance hyperspectral imaging to the investigation of ancient metallographic artifacts is presented here. So far this technique has been used for diagnostics of polychrome surfaces, but it has never been applied to investigation of metallic surfaces. Hyperspectral imaging in the VIS-NIR range (400-1700 nm) was applied on replicas of a historical object from the archaeological site of Kobilic (Croatia). The same replicas were analyzed also using neutron tomography. Hyperspectral data were elaborated to map the distribution of the different phases on the surface. The comparison of the hyperspectral data with the neutron tomography data-images provided prominent similarities. These preliminary results encourage further investigations on merging these two imaging techniques for novel applications on archeo-metallurgy.

Terahertz time-domain imaging (THz-TDI) and Spectral domain optical coherence tomography (SD-OCT) are two investigation methods capable of providing 3D datasets from which depth profiles, cross-sectional images, plan-type images and volume rendering of an object can be derived. These novel photonic technologies are extremely relevant to the field of heritage science, for which the comprehension of the stratigraphic structure of a cultural heritage object may help in the understanding of its manufacturing technology and state of preservation. Different imaging depths, fields of view and axial/lateral resolutions characterize the two imaging technologies, which thus provide different but complementary information of the same scanned object. In this study we show how the THz-TDI and SD-OCT scans performed on a fragment from the underside of an Egyptian coffin (Theban area, 21st/22nd Dynasties, Egyptian Antiquities department of the Louvre museum, Paris, France) gave precious insights on its full structure and stratigraphy.

Heritage science aims to study cultural heritage objects through the developing and studying conservation issues to advise new restauration approach. In addition, the development of new tools is one of the major accesses, which allows to increase knowledge in archaeology and to characterize the materials. This paper is focused on the development of a Laser-Induced Breakdown Spectroscopy-Laser-Induced Fluorescence-Raman Spectroscopy (LIBS-LIF-Raman) portable instrument for supporting conservation campaigns when extensive measurements and on-site decision-making in cultural heritage. Such a multi-analytical prototype instrument is able to combine these three laser-based spectroscopic techniques to simultaneously provide complementary elemental and molecular information from the same analysis point. To that purpose, different laser sources, appropriate optics and detection modules have to be examined in order to integrate them on a mobile platform.

The Taj Mahal, a 17th century architectural wonder is known worldwide for its visual appeal in white marble with beautiful inlay works in the style of ‘Pietra Dura’ from Florence, Italy. The long-drawn restoration process for structural damage and surface discoloration of this heritage structure has drawn international attention. The conventional means of structural survey is based mostly on visual assessments by experts which is highly time-consuming and subjective; and in most cases can be done only after the damages become apparent. Consequently, the restoration involves exhaustive repair procedures. In this work, we have introduced a combination of optical imaging and spectroscopy techniques, namely, µ-Raman Spectroscopy and Terahertz Time Domain Spectroscopic Imaging, as an alternative approach for both surface and subsurface damage detection in Marble structures. In our work, we have examined some of the most common structural and surface damages in heritage Marble architectures found worldwide using some selected representative models. These model slabs bearing similar ornamental colourful motifs like those in the Taj Mahal were probed by the above two techniques, which showed tremendous promise in sensing very fine cracks which are visually impossible to detect. Also, minute changes in surface quality due to the introduction of organic materials were mapped with high accuracy. This paves the way for an efficient and trusted survey platform that could be deployed in future which would be able to provide a fast and reliable structural assessment of our cultural heritage architectures for the next generation.

Infrared thermography is a non-destructive testing technique that affects many areas. This technique of analysis is, for example, very interesting in the field of restoration and conservation of heritage works. The possibilities of active thermography can help in the early detection of defects in works of art and their characterization. In this work we will demonstrate that it is possible to detect old restorations in frescoes and murals by flash method. This new possibility offered by thermography will make it possible, for example, to verify the compatibility of a restoration with the original work, which can prevent the appearance of a defect and may allow the conservator to follow up on restoration. First we will show the feasibility of this approach on a laboratory specimen containing different types of clogging materials and then present results of analysis carried out in situ at one restoration sites that reveal the possibility of locating these restorations but also to characterize the pictorial technique used in this one.

Israel in Egypt is an oil on canvas painting by Sir Edward Poynter. In 1868 the painting was depicted in the Illustrated London News in which there are reports of changes made to the composition of the painting after its first exhibition. Visible and infrared imaging techniques have been used to determine whether additions to the initial composition can be identified from underdrawings. The painting measures 137 cm × 317.5 cm and was not able to be relocated for the study, therefore portable imaging equipment was used throughout. A Canon 700D DSLR camera was modified to allow nearinfrared imaging when combined with a set of longpass filters at 720 nm, 850 nm and 950 nm. An Osiris infrared reflectography camera was also used to look further into the infrared with a sensitivity range of 900 nm – 1700 nm. To obtain high-resolution images with the modified DSLR, a 100 mm lens was used from a distance of 6 metres. In both visible and near-infrared, eight images were taken across the surface of the painting and these images were combined into high-resolution visible and near-infrared panoramas. Images from the Osiris infrared camera were processed in Matlab to create a mosaic from the overview image with high-resolution regions of interest. All processed images were registered in Matlab along with the woodcut engraving of the painting shown in the Illustrated London News. An interactive web-browser viewer was created to enable display and comparison of the registered high-resolution images, allowing users to explore and zoom in to specific areas of interest across the four high-resolution images simultaneously. Conservators and art historians can utilise the resulting images combined with the image viewer to analyse the painting and potentially develop a new interpretation of the composition.

The main purpose of this contribution is to report some first preliminary analyses of a new and never investigated decorative technique named Tattoo Wall, especially the possible changes due to ageing artificially induced by extreme humidity conditions in view of a possible application in crypts, churches or outside wall paintings. This innovative decorating technique involves transferring digital images on wall surfaces through a transfer paper with solvent-based ink and fixative. For the experimental tests, we chose to work on a color scale as wide as possible, to test each single color, and on different materials. The printed colors were applied on hydraulic mortar, containing marble powder combined with Ledan C30, particularly suitable for restoration in environments with high relative humidity (RH%). Moisture ageing was obtained by placing the sample in a box with RH% fixed to 92% thanks to the presence of salts (sodium sulphate deca-hydrated) for compressively two years (96 weeks). Reflectance spectrophotometry for color measurements and hyperspectral imaging (HSI) were used to assess the effect of high relative humidity exposure. The experimental data were statistically treated in order to evaluate their significance. Testing enabled us to verify the stability and durability of Tattoo Wall® under high relative humidity, with little chromatic alterations. Testing could and should be conducted also on different surfaces and materials (paintings on canvas and wood, oil on wall, etc.) to make it as complete as possible and guarantee the use of Tattoo Wall® in most cases of pictorial reintegration, reducing the risk of human error.

IRT has been used as a first investigation in laboratory to detect pioneer biofilms which help the biological fouling of stone monuments. Biological development is often removed because of the unsightly aspect and it favours stone deterioration with mineral dissolution by production of organic acids, salting induces physical damage which helps to the development of macroscopic vegetation. Biological deterioration leads to the degradation of stone monuments and to the irretrievable loss of artefacts for our Cultural Heritage. Two limestones, Courville and Savonnieres stones used in major buildings in eastern France and the surroundings of Paris have been investigated. On first, stone samples have been exposed in outdoor test to favour the natural colonisation of first micro-organisms. They have been collected after six months exposure and compared to three non-colonised stones throughout IRT measurements of stone surfaces pulsed by a flux of photons. First results on Courville stone, showed Look Up Table (LUT) was important to emphasize slight variations of static images between stones with biofilm and control stones without it. Moreover, mathematical post-processing as SVD, usually applied to decrease thermal artefacts at the surface of a work of art and to improve detection of flaws inside it, here was to detect biofilms as surface artefacts thanks to the first EOFs. Savonnieres stone, which has different intrinsic properties than Courville stone showed static images can induced artefact associated to experimental conditions which was avoided thanks to SVD post-processing.

The basic material of library collections is paper. There occur also other kinds of materials in libraries, especially collagen materials – parchment and leather, but also textile, and in modern collections also plastic. Project "Advanced techniques of cleaning of books and manuscripts" (identification code DG18P02OVV048) is supported by the Ministry of Culture of the Czech Republic in 2018-2022. The main goal of the project is to develop techniques suitable for cleaning of the mentioned library materials by laser and by carbon dioxide snow. Cleaning will be carried out on model samples at first, then on real library objects. To optimize parameters of both cleaning techniques, it is fundamental to select method of evaluation of their effectiveness in removing dirt and dust, and at the same time the method of observation, whether undesirable changes in cleaned materials do not occur during cleaning, i.e. their degradation. For orientation evaluation of effectiveness of cleaning, measurement of colour scheme was used in L*a*b* colour space, in particular evaluation of parameter L*. Multifunction microscope Hirox serves for measurement of roughness and wetting power of material surfaces, which may change as a result of damage of integrity of collagen fibres. Also use of scanning electron microscope imaging is of advantage for finding the degree of deterioration of integrity of collagen fibres. Degradation of leather and parchments will also be monitored by measurement of changes in shrinkage temperature using hot table microscopic technique.

The murals of the Tang Tomb are important materials for studying the social life of the Tang Dynasty, which have important protection and research value. In order to protect the tomb murals as longer as possible, it is necessary to restore the murals and accurately record the restore location. Nevertheless,the restored murals are difficult to observe directly the restore area through the human eye. This paper proposes a method to reveal the restored areas, by extracting the main components of the Multi-Hyper-spectral image of the mural with the Minimum Noise Fraction (MNF) Rotation, and the location of the restored area is clearly observed from the main component. In addition, the mural sketch reflects the main content of the mural of the Tang Tomb murals, which are of great significance to the restoration and protection of the Tang Tomb murals. In this paper, we also proposed a new method to extract the sketch of Tang Tomb mural. For the bands sensitive to the composition of the sketches, the sparsely constrained sparse non-negative matrix under- approximation method is used to decompose the optimal sketches composition, and then the sketches are automatically extracted based on the idea of layer superposition. Through the experiments on the mural paintings in the three tombs, the results demonstrated that the proposed method could effectively perceive the area of mural restoration and automatically extract the sketch accurately and clearly, while saving manpower.

In recent years, smartphones have developed tumultuously; in fact, they have increasingly taken on the role of portable and compact personal computers equipped with a range of sensors and applications capable of monitoring, for example, physical activity, heartbeat and sleep. Their ability to manage and transmit data makes them a very interesting tool even in the scientific field, where the concept of “lab in a phone” is gaining ground. In this work, after briefly summarizing these new approaches, we will consider the application of smartphones to the diagnostics of Cultural Heritage.

The Agris Helmet is a masterpiece of the Celtic art made in the middle of the 4th century A.D. It has been found near Agris, France, in 1981 during an archeological dig under the supervision of José Gomez-de-Soto. This composite object is made of an iron cap covered with bands of bronze. The bronze is itself covered with pure gold leaf, with embedded coral decorations attached using silver rivets. The Helmet was discovered with one cheek guard which had similar materials and designs. Considering this information, the cap would have been used for display rather than worn in battle. The helmet, discovered in pieces, was restored in Mainz during the 1980th and is now held by the Musée d'Angoulême in Angoulême (France). The present project led jointly by the AOROC department of the ENS and the C2RMF and supported by PSL, was an opportunity to make complementary work on the Helmet to document it thoroughly. Our aim was threefold. Firstly, we wanted to document the Helmet in such a way that future studies would be doable even without physical access to the original piece. Then, we were willing to search the best 3D technique and practice for this complex piece. The level of details and the brilliant aspect of the surface were the perfect challenges for our 3D systems. In addition to these technics, we wanted to enhance the knowledge about the object (material and technical identification) and provide new data for archaeology and art history. We began the study with a complete photographic coverage of the Helmet thus highlighting every single visible detail on its surface. In order to go further concerning the structure of the object itself, we chose to use X-Ray technology. This method allowed us to see behind the surface and understood the organization and construction of the Helmet. Furthermore, multiple techniques of photogrammetric imaging and 3D digitalization were used to obtain the best set of data. Leadingly, we performed a photogrammetric coverage under artificial lights followed by another under natural light. Thereafter, we used two 3D scanners technologies, one based on structured light and the second based on laser technology. The resulting 3D models were compared in precision and acquisition convenience (simplicity of devices and acquisition time). While the photogrammetric models were perfect to easily visualize the texture and color of the object, its degree of precision left something to be desired. On the contrary, the 3D models obtained by scanning technologies were effective for the purpose of getting complete metric and volumetric values. For the study of the Helmet, the high-resolution models provided information about tools marks and other traces of the production techniques. Moreover, mesh comparing provided new data for the matching of supposedly identical items on the surface. The results of those studies were particularly instructive for the historians of the Celtic period and gave new possibilities to the researches for the work on this precious object.

The complementary use of X-ray fluorescence (XRF) mapping, spectral imaging, and Raman mapping, allows for the analysis and identification of important artistic materials used in the production and illustration of illuminated manuscripts. This project uses combined non-invasive imaging techniques to analyse 17th – 19th century manuscripts from the British Library’s Southeast Asia Collections so that more can be understood about the adoption and evolution of artistic materials and techniques used in Maritime Southeast Asia. Using multiple different imaging techniques has shown to provide positive results, however, a consequence of this is the collection of large amounts of data, necessitating the automatic and unsupervised analytical techniques used in machine learning. Data collected in-situ at the British Library using macro-XRF mapping, macro-Raman mapping, and Spectral Imaging, will be analysed using a range of machine learning techniques to cluster pixel information representing materials used in southeast Asian manuscripts.

Four paintings of David Lynch’s cycle from the period 1996-2001 were investigated in order to propose proper conservation treatment. Non invasive elemental analyses with portable XRF indicated traditional pigments like cadmium red, iron black, ivory black. The main material of unknown origin used as paint contained significant amounts of alumina, magnesium and additions of silica and iron. SEM-EDX and FTIR analyses conducted on samples enabled further recognition. Material used as paint was chlorinated polyethylene close to the industrial product Agitan P 813. Coating used instead of typical artists’ varnishes proved to be alkyd resin. In carpenters’ glue used by artist for “consolidation” repairs polyvinyl chloride was detected as the main component. For the primer acrylic medium with chalk and titanium white was used. Artist was insisted to help to identify unexpected non-traditional materials. He revealed that elastomeric Taylor 2080 Adhesive for gluing carpets was executed as paint and for the coating - Man O’War Marine Spar Varnish for garden wooden furniture of McCloskey company. The amorphous silica indicated by the lacquer’s producer as ingredient was identified and visualized in the SEM-EDX. Consolidating adhesive was the Titebond III Ultimate Wood. Investigation revealed wide use of non-artistic materials by David Lynch. Recognized materials enabled to propose modified cleaning treatment based on buffered water solution of controllable pH (5) and conductivity (5,5 mS) resulting in successful cleaning of the works. Paper is a case study of material recognition of technique of contemporary works of art of basic importance to propose its proper conservation treatment.