The present study investigates the effects of various cadmium-based pigments on the curing behaviour of linseed oil. Model linseed oil paints, prepared starting from different cadmium yellow pigments, were subjected to accelerated aging inside a thermobalance at 80 °C, under oxygen flow and in the dark. Thermogravimetric analysis (TGA) was used to monitor the mass change of the paint samples induced by oil autoxidation during curing, while ATR-FTIR spectroscopy provided insights into molecular transformations before and after thermal exposure. Results reveal that cadmium yellow pigments with identical chemical composition (CdS) can induce different curing kinetics, depending on the crystalline features of the pigments, namely crystallite size and degree of crystallinity. Pigments having nanocrystalline structures delayed the onset of peroxide propagation, resulting in extended induction times and incomplete polymer network formation in the timeframe investigated. These paints also showed formation of cadmium carboxylates and cadmium sulphates. These results may be related to the intrinsic peroxidase-like (POD-like) catalytic activity of nanocrystalline CdS, reported here for the first time in a non-aqueous medium.

Natural ultramarine blue is a well-studied pigment, yet the assessment of its quality and purity in works of art remains challenging. This work addresses this issue by establishing an innovative analytical protocol based on micro-Raman mapping to assess detailed compositional information and enable the complete statistical evaluation of the composition of ultramarine blue in paint stratigraphic samples. The experimentation has involved the analysis of several standards of natural ultramarine pigment powders, with different purity grades used to train the Raman technique in mineral identification. The study focused on the identification of the mineral lazurite, which is responsible for the blue colour, and on the associated silicates, carbonates, oxides, phosphates and sulphides associated with the mineral from which the pigment derives. This holistic approach has allowed the selection of diopside as a purity marker of the pigment. Significant differences in the statistical molecular analysis related to the purity grade of the pigment have allowed for the first time to make considerations regarding the quality of the blue pigment in some paint cross-sections from old master paintings from the Courtauld Gallery in London. These samples were also analysed using Synchrotron-based micro-X-Ray Powder Diffraction (SR μ-XRPD) mapping, confirming compositional information gained from the vibrational analysis. The results of this study provide a novel method for the characterisation of different grades of ultramarine blue pigment used in works of art. This data, together with context provided by historical and social information, will aid authentication attribution and inform conservation interventions based on a thorough knowledge of its molecular composition.

Over the last few years, contemporary mural paintings have gained significant importance as both artistic and social expressions within urban environments. The study focuses on the characterization of the faded painting materials from a case study in Milan, 20 years of Freedom and Democracy, and its aesthetic, morphological and chemical alterations. The goal is to study the phenomenon of chromatic alteration and understanding causes and mechanisms. In this work, a diagnostic study based on non-destructive and micro-destructive investigation methods is presented, improving and integrating the knowledge about Street Art deterioration. The colour fading of this mural was clearly evident from the available online photographic documentation, which allowed the reconstruction of the evolution of its appearance over time since its realization. The analysis revealed that colour fading occurred within the first two years. A wide range of analytical techniques were employed to gain deeper insights into the qualitative and semi-quantitative composition of the materials. These included hyperspectral imaging, microscopy observations and molecular and elemental spectroscopies of collected paint samples (mu -FTIR ATR and reflectance mapping, mu -Raman spectroscopy, FE-SEM observation and EDXS mapping). Colour fading was found to affect less than 10 mu m of the surface. The deterioration of the polymeric binder promotes the loss of pigments and therefore the enrichment of white fillers on the surface, the so-called chalking effect, in agreement with other studies on Street Art murals. Furthermore, the photochemical instability of specific pigments (PR112, C.I.:12370 and PY83, C.I.:21108) was demonstrated, leading to the dramatic colour changes observed on the real surface.

In several manuscripts, text is obscured due to glued together leaves, making it difficult or impossible to read. In this context, this study explores the use of reflectance and transmittance imaging spectroscopy (RIS and TIS) in the visible and near-infrared range (400-1000 nm) to recover hidden texts. The method is applied to two cases of medieval Frisian legal codes from the Richthofen Collection, where we employed Non-Negative Matrix Factorization (NMF) for the analysis of single and spectrally fused datasets integrating both RIS and TIS. We further integrated spatial stitching of adjacent areas to enhance spatial resolution of the images. Our results demonstrate that factorization algorithms perform well on fused datasets, with spectral fusion proving essential in complex cases where individual analyses fail to clearly reveal hidden text.

This study explores the early detection of degradation in plastic-based cultural heritage objects using non-invasive spectroscopic techniques. The results on artificially aged ABS specimens revealed degradation markers at low exposure levels. Changes in polymer composition were then correlated with mechanical stiffening and increased friction. The approach offers valuable tools for in situ monitoring and preventive conservation of modern art and design objects.

We assess a hyperspectral imaging system for characterizing biological tissue spectral properties. The setup comprises a hyperspectral camera ($400-1000 ~\text{nm}$) and two halogen lamps. First, we assess image quality by quantifying spatial inhomogeneity using an optically-homogeneous phantom. Second, we evaluate measurement robustness to varying objectivespecimen distance and lamp orientation. Finally, we evaluate the validity of the measurement system by comparing hyperspectral measurements of five colored Spectralon samples with reference data from a spectrometer. Our results demonstrate minimal spatial variability within the images ($<3 \%$ before data normalization, < 1% after data normalization) in the $500-900 ~\text{nm}$ range when measuring the homogeneous phantom, indicating artifact-free imaging. Additionally, the measured reflectance spectra exhibit low ($<5 \%$) variability across different objective-specimen distances and lamp orientations, suggesting robustness to setup configuration changes. Finally, the spectral measurements of the Spectralon samples closely match the spectrometer reference data. These findings support the use of our system for material spectral characterization.

The application of X-ray methods (using conventional sources or synchrotron radiation) for investigating degradation phenomena in paintings has significantly increased in the last two decades. This rise is due to their ability to provide spatially resolved elemental, molecular, and structural information from the macroscopic to the nanoscopic levels. This review will focus on the application of latest-generation X-ray techniques, including X-ray fluorescence (XRF), X-ray absorption spectroscopy (XAS), and X-ray diffraction (XRD), to study the alteration processes of pigments in paintings. The first part outlines the fundamentals of XRF, XAS, and XRD techniques and then describes the corresponding instrumental set-ups used for non-invasive macro-scale mapping of paintings and synchrotron radiation-based X-ray analysis of paint micro-samples. Subsequent sections will cover advancements in X-ray data analysis software, workflow management systems, Open Science and FAIR data initiatives, alongside practical aspects of sample preparation and issues concerning X-ray-induced damage to paints. The final section will review degradation phenomena resulting from chemical changes of selected classes of pigments. This will involve describing key findings obtained from paintings, related micro-samples, and artificially aged paint mock-ups. The outcomes discussed in this review highlight their crucial role in developing effective monitoring and preventive conservation strategies for artworks highly susceptible to degradation within heritage sites and museums.

The study of cultural heritage (CH) objects benefits greatly from non-invasive techniques like hyperspectral imaging (HSI), which enables material identification and spatial mapping. Due to the heterogeneous composition of CH artifacts, combining complementary techniques is essential for comprehensive analysis. However, handling such high-dimensional datasets remains a challenge. We present a computational protocol that combines spatial and spectral dimensionality reduction to enable early-stage fusion and efficient analysis of fused data, through multivariate methods, with a focus on Uniform Manifold Approximation and Projection (UMAP). We introduce an open-source plugin for Napari viewer, which allows for UMAP-based exploration of fused multimodal datasets. Our approach is demonstrated in case studies involving reflectance and photoluminescence data fusion, showcasing its effectiveness in detecting degradation phenomena and revealing material complexity in both plastic artifacts and historical paintings.

The exceptionally high NIR photoluminescence of the ancient pigment Egyptian blue is due to its very stable phase cuprorivaite (CaCuSi4O10). This compound has recently attracted significant attention, leading to numerous applications for sensors, luminescent solar concentrators, energy-saving, and biomedicine. Here we report an innovative manufacturing process for producing high-grade cuprorivaite, characterized by fine crystal grains and a significantly increased NIR photoluminescence emission. The unprecedented ultra-high NIR emission (quantum yield phi EM approximate to 30 %) is almost three times higher than the best one reported so far. This is an important turning point for the extension of applications of cuprorivaite to new sectors and can greatly boost its exploitation. The new high-efficiency cuprorivaite is obtained by solid-state synthesis, using silica nanoparticles as a starting material and avoiding fluxing agents. No doping with rare-earths or other elements has been employed, making synthesis straightforward and sustainable. The material obtained has been fully characterized in terms of crystalline, morphological, and optical properties and compared to cuprorivaite obtained through traditional melt-flux synthesis. The main difference observed is that the tiny crystals obtained through the new synthesis method are practically devoid of the glassy phase, rich in copper and impurities, that is instead largely present in Egyptian Blue pigment synthesized with traditional melt-flux synthesis. We speculate that this glassy phase is responsible for the partial suppression of the intrinsic photoluminescence of cuprorivaite, demonstrating how limiting the glassy phase can increase the external quantum efficiency of Egyptian blue.

Throughout the 20th Century, plastics found extensive use in fashion, art, and design due to their versatile nature. However, their degradation over time poses challenges, impacting material integrity, particularly in museum collections. To tackle this issue, different scientific techniques have been employed to study polymers. In this work, a complementary multi-analytical approach is proposed to investigate the light stability of ABS compounds, selecting LEGO® bricks as reference material. The method is based on fluorescence emission and lifetime integrating point-like analysis and imaging systems to corroborate chemical and spatial information specifically addressed at the surface level. The latter has shown promising results in studying ABS objects, offering insights into degradation and aiding conservation efforts.

Hyperspectral imaging (HSI) has emerged as an effective tool to obtain spatially resolved spectral information of artworks by combining optical imaging with spectroscopy. This technique has proven its efficacy in providing valuable information both at the large and microscopic scale. Interestingly, the macro scale has yet to be thoroughly investigated using this technology. While standard HSI methods include the use of spatial or spectral filters, alternative methods based on Fourier-transform interferometry have also been utilised. Among these, a hyperspectral camera employing a birefringent common-path interferometer, named TWINS, has been developed, showing a high robustness and versatility. In this paper, we propose the combination of TWINS with a macro imaging system for the study of cultural heritage (CH). We will show how the macro-HSI system was designed, and we will demonstrate its efficient capabilities to collect interferometric images with high visibility and good signal of both reflectance and fluorescence on the same field of view, even on non-flat samples. Our hyperspectral camera for macro studies of both reflectance and fluorescence data is a completely new asset in the CH panorama and beyond. The relevance of the macro technology is demonstrated in two case studies, aiding in the analysis of biofilms on stone samples and of the degradation of dyed textiles.

A class of hyperspectral imaging systems operating on an extremely wide spectral range has been developed based on a new compact and reliable interferometer. The systems are portable and feature high throughput and low noise.

This paper introduces a novel multimodal optical microscope, integrating Raman and laser-induced photoluminescence (PL) spectroscopy for the analysis of micro-samples relevant in Heritage Science. Micro-samples extracted from artworks, such as paintings, exhibit intricate material compositions characterized by high complexity and spatial heterogeneity, featuring multiple layers of paint that may be also affected by degradation phenomena. Employing a multimodal strategy becomes imperative for a comprehensive understanding of their material composition and condition. The effectiveness of the proposed setup derives from synergistically harnessing the distinct strengths of Raman and laser-induced PL spectroscopy. The capacity to identify various chemical species through the latter technique is enhanced by using multiple excitation wavelengths and two distinct excitation fluence regimes. The combination of the two complementary techniques allows the setup to effectively achieve comprehensive chemical mapping of sample through a raster scanning approach. To attain a competitive overall measurement time, we employ a short integration time for each measurement point. We further propose an analysis protocol rooted in a multivariate approach. Specifically, we employ non-negative matrix factorization as the spectral decomposition method. This enables the identification of spectral endmembers, effectively correlated with specific chemical compounds present in samples. To demonstrate its efficacy in Heritage Science, we present examples involving pigment powder dispersions and stratigraphic micro-samples from paintings. Through these examples, we show how the multimodal approach reinforces material identification and, more importantly, facilitates the extraction of complementary information. This is pivotal as the two optical techniques exhibit sensitivity to different materials. Looking ahead, our method holds potential applications in diverse research fields, including material science and biology.

This work introduces a novel method to multivariate analysis applied to fused hyperspectral datasets in the field of Cultural Heritage (CH). Hyperspectral Imaging is a well-established approach for the non-invasive examination of artworks, offering insights into their composition and conservation status. In CH field, a combination of hyperspectral techniques is usually employed to reach a comprehensive understanding of the artwork. To deal with hyperspectral data, multivariate statistical methods are essential due to the complexity of the data. The process involves factorizing the data matrix to highlight components and reduce dimensionality, with techniques such as Non-negative Matrix Factorization (NMF) gaining prominence. To maximize the synergies between multimodal datasets, the fusion of hyperspectral datasets can be coupled with multivariate analysis, with potential applications in CH. In this work, I will show examples of this approach with different combinations of datasets, including reflectance and transmittance spectral imaging, Fluorescence Lifetime Imaging and Time-Gated Hyperspectral Imaging, and Raman and fluorescence spectroscopy micro-mapping.

Ultramarine Blue (UB) pigment, derived from lapis lazuli, holds a significant place in the history of late medieval and Renaissance Europe, owing to its unusually bright colour and stability. Its prohibitive price, which equalled that of gold, meant that it was only used by estimated artists. In this work we present a non-invasive, multimodal approach to the characterization of the photoluminescent properties of different variants of the pigment. The ultimate goal of this research is to propose a protocol for the identification of UB in artworks thanks to the combination of Raman spectroscopy and time resolved-photoluminescence spectroscopy and imaging.

Ludwig van Beethoven (1770 -1827) used to record his ideas in sketchleaves and sketchbooks, where he collected preparatory materials before publishing his final work. These handwritten documents are rich in information. Nonetheless, as a consequence of the creative process, the annotations are much reworked by the composer itself, making them hard to interpret. This study aims, for the first time, at a non -invasive characterization of the inks used by Ludwig van Beethoven in his manuscripts. Distinguishing the inks used for the notes and the rewritten or modified parts would allow a better comprehension of his creative process. With this purpose, the manuscript BG0044 Piatti-Lochis PREIS.J1.9686, held at the Angelo Mai Civic Library of Bergamo (Italy), was investigated by exploiting portable imaging and spectroscopic techniques. The photographic documentation under Visible (VIS) and Ultraviolet light (UVIF) illumination, along with the Hyperspectral Imaging (HSI) in the spectral range 450 nm to 1000 nm were essential to identify the areas of interest for further analysis and provide a working hypothesis on the inks used by Beethoven. Afterwards, X -Ray Fluorescence (XRF) spectroscopy was employed to get an insight into the chemical composition of the inks. The foremost result revealed the presence of two different iron-based inks, used for the staves and the handwritten musical notations, respectively. The superimposed strokes observed among the staves on the same material composition led us to suppose that they have been applied immediately to the paper or in a limited time during which the same ink recipe was maintained. Hence, it seems that the composer made changes almost at the same time as he wrote the first version. These results represent the first scientific evidence to endorse the hypothesis of a rapid change of mind in his writing process.

The present study describes an innovative approach for the study of time-dependent alteration processes. It combines an advanced hyperspectral imaging (HSI) system, to collect visible reflectance and fluorescence spectral data sets sequentially, with a tailored multiblock data processing method. This enables the modeling of chemical degradation maps and the early, spatially resolved detection of dye alteration in textiles. A chemometric method based on data fusion and principal component analysis was employed to identify spectral features of dye degradation, combining and enhancing information from reflectance and fluorescence HSI data. The most significant spectral profiles extracted were used to develop an asymmetric Gaussian-based pixel-by-pixel fitting model applied to the HSI fluorescence data set, enabling the reconstruction of degradation maps for rapid and intuitive visualization. In particular, changes in intensities and horizontal shift of dye emission peaks were pixel-by-pixel evaluated and fitted for the reconstruction of the degradation maps. Artificially aged wool samples tinted with indigo carmine (IC) dye served as a case study. IC is extensively used in textiles, and it is notable for its light sensitive. The results show that this approach effectively identifies spatial variations and chemical changes in dyed wool fibers, offering potential for sustainable conservation of historical textiles and other types of time-dependent processes. Thus, by amplifying variation in spectral profiles induced over time by aging, even minimal changes at early stages can be easily detected and localized, offering powerful tools for future studies on food and drug shelf life and stability, as well as forensic trace analysis.