Microporous electrospun nonwovens combined with green solvents for the selective peel-off of thin coatings from painting surfaces.

Over the last few decades, significant research efforts have been devoted to developing new cleaning systems aimed at preserving cultural heritage. One of the main objectives is to selectively remove aged or undesirable coatings from painted surfaces while preventing the cleaning solvent from permeating and engaging with the pictorial layers. In this work, we propose the use of electrospun polyamide 6,6 nonwovens in conjunction with a green solvent (dimethyl carbonate). By adjusting the electrospinning parameters, we produced three distinct nonwovens with varying average fiber diameters, ranging from 0.4 µm to 2 µm. These samples were characterized and tested for their efficacy in removing dammar varnish from painted surfaces. In particular, the cleaning process was monitored using macroscale PL (photoluminescence) imaging in real-time, while post-application examination of the mats was performed through scanning electron microscopy. The solvent evaporation rate from the different nonwovens was evaluated using gravimetric analysis and Proton Transfer Reaction- Time-of-Flight. It was observed that the application of the nonwovens with small or intermediate pore sizes for the removal of the terpenic varnish resulted in the swollen resin being absorbed into the mats, showcasing a peel-off effect. Thus, this protocol eliminates the need for further potentially detrimental removal procedures involving cotton swabs. The experimental data suggests that the peel-off effect relates to the microporosity of the mats, which enhances the capillary rise of the swollen varnish. Furthermore, the application of these systems to historical paintings underwent preliminary validation using a real painting from the 20th century.

Near-infrared hyperspectral imaging to map collagen content in prehistoric bones for radiocarbon dating.

Many of the rarest prehistoric bones found by archaeologists are enormously precious and are considered to be part of our cultural and historical patrimony. Radiocarbon dating is a well-established technique that estimates the ages of bones by analysing the collagen still present. However, this method is destructive, and its use must be limited. In this study, we used imaging technology to quantify the presence of collagen in bone samples in a non-destructive way to select the most suitable samples (or sample regions) to be submitted to radiocarbon dating analysis. Near-infrared spectroscopy (NIR) that was connected to a camera with hyperspectral imaging (HSI) was used along with a chemometric model to create chemical images of the distribution of collagen in ancient bones. This model quantifies the collagen at every pixel and thus provides a chemical mapping of collagen content. Our results will offer significant advances for the study of human evolution as we will be able to minimise the destruction of valuable bone material, which is under the protection and enhancement of European cultural heritage and thus allow us to contextualise the valuable object by providing an accurate calendar age.

Towards the non-destructive analysis of multilayered samples: A novel XRF-VNIR-SWIR hyperspectral imaging system combined with multiblock data processing.

The new challenge in the investigation of cultural heritage is the possibility to obtain stratigraphical information about the distribution of the different organic and inorganic components without sampling. In this paper recently commercialized analytical set-up, which is able to co-register VNIR, SWIR, and XRF spectral data simultaneously, is exploited in combination with an innovative multivariate and multiblock high-throughput data processing for the analysis of multilayered paintings. The instrument allows to obtain elemental and molecular information from superficial to subsurface layers across the investigated area. The chemometric strategy proved to be highly efficient in data reduction and for the extraction and integration of the most useful information coming from the three different spectroscopies, also filling the gap between data acquisition and data understanding through the combination of principal component analysis (PCA), brushing, correlation diagrams and maps (within and between spectral blocks) on the low-level fused. In particular, correlation diagrams and maps provide useful information for the reconstruction of a stratigraphic structure without the need to take any sample, thanks to the effective account for inter-correlation among data (variables), which is able to effectively characterize the possible combinations of components located in the same depth level. The highly innovative technology and the data processing strategy are applied for the multi-level characterization of a complex painting reproduction as an illustrative pilot study.

A non-invasive diagnostic tool for cellulose acetate films using a portable miniaturized near infrared spectrometer.

This article tests the suitability of a new method to monitor the degree of substitution of cellulose acetate films, by employing a compact and inexpensive near-infrared miniaturized spectrometer (908.1-1676.2 nm) that can be easily applied in situ. The present study compares the analytical performance of the proposed method against conventional diagnostic strategies based on benchtop micro-attenuated total reflectance Fourier transform Infrared (µATR -FTIR) measurements in the mid-infrared spectral range. The novel calibration function exploits the shifts in the first overtone of the hydroxyl stretching 2νOH band of probe materials and was created using a set of analytical standards with different degrees of substitution. The robustness of the method was assessed by application on a group of sixteen historical cinematographic films. The accurate condition assessment of these films was performed in situ, in a non-invasive manner. The proposed analytical procedure is quick and easy-to-implement, and therefore it constitutes a rapid method to guide conservation strategies regarding film storage and digitalization in cultural institutions, including museums and cinematheques. Potential applications on three-dimensional objects and industrial processes are possible.

Quantifying spatial variation in the uptake of microplastic by mussels using biodeposit traps: A field-based study.

Spatial uptake patterns of microplastics (MP) by marine species are largely unexplored under field conditions. A novel "biodeposit trap" that measure uptake and egestion of MP by suspension-feeders through the analysis of their biodeposits, was designed and used to estimate the spatial variation of these processes by mussels in field conditions. Traps containing wild or farmed mussels or control empty shells were deployed at three sites characterised by different MP concentrations and water flow conditions. A different MP dimensional composition was observed between MP pools present in biodeposit and control traps, with the latter shifted towards higher dimensional range (0.05-5 mm). Conversely, mussels accumulated small MP (0.02-0.05 mm) into their biodeposits without any significant difference between wild and farmed specimens. MP uptake rates were on average 4-5 times higher at the site where MP contamination was expected to be highest and where water flow conditions were considered moderate.

An effective strategy for the monitoring of microplastics in complex aquatic matrices: Exploiting the potential of near infrared hyperspectral imaging (NIR-HSI).

Contamination by microplastics (MP) represents a critical environmental challenge with potential consequences at ecosystem, economic and societal levels. As the marine system is the final sink for MP, there is an urgent need to develop methods for the monitoring of synthetic particles in different marine compartments and sample matrices. Extensive evaluations are hindered by time and costs associated with to conventional MP spectroscopic analyses. The potential of near infrared hyperspectral imaging (NIR-HSI) has been recently evaluated. However, NIR-HSI has been poorly studied so far, limitedly to the detection of large particles (>300 µm), and its capability for direct characterization of MP in real marine matrices has not been considered yet. In the present study, a rapid near infrared hyperspectral imaging (NIR-HSI) method, coupled with a customised normalised difference image (NDI) strategy for data processing, is presented and used to detect MP down to 50 µm in environmental matrices. The proposed method is largely automated, without the need for extensive data processing, and enabled a successful identification of different polymers, both in surface water and mussel soft tissue samples, as well as on real field samples with environmentally occurring MP. NIR-HSI is applied directly on filters, without the need for particles pre-sorting or multiple sample purifications, avoiding time consuming procedures, airborne contaminations, particle degradation and loss. Thanks to the time and cost effectiveness, a large-scale implementation of this method would enable to extensively monitor the MP presence in natural environments for assessing the ecological risk related to MP contamination.

Organogel Coupled with Microstructured Electrospun Polymeric Nonwovens for the Effective Cleaning of Sensitive Surfaces.

Hydrogels and organogels are widely used as cleaning materials, especially when a controlled solvent release is necessary to prevent substrate damage. This situation is often encountered in the personal care and electronic components fields and represents a challenge in restoration, where the removal of a thin layer of aged varnish from a painting may compromise the integrity of the painting itself. There is an urgent need for new and effective cleaning materials capable of controlling and limiting the use of solvents, achieving at the same time high cleaning efficacy. In this paper, new sandwich-like composites that fully address these requirements are developed by using an organogel (poly(3-hydroxybutyrate) + γ-valerolactone) in the core and two external layers of electrospun nonwovens made of continuous submicrometric fibers produced by electrospinning (either poly(vinyl alcohol) or polyamide 6,6). The new composite materials exhibit an extremely efficient cleaning action that results in the complete elimination of the varnish layer with a minimal amount of solvent adsorbed by the painting layer after the treatment. This demonstrates that the combined materials exert a superficial action that is of utmost importance to safeguard the painting. Moreover, we found that the electrospun nonwoven layers act as mechanically reinforcement components, greatly improving the bending resistance of organogels and their handling. The characterization of these innovative cleaning materials allowed us to propose a mechanism to explain their action: electrospun fibers play the leading role by slowing down the diffusion of the solvent and by conferring to the entire composite a microstructured rough superficial morphology, enabling to achieve outstanding cleaning performance.

A new miniaturised short-wave infrared (SWIR) spectrometer for on-site cultural heritage investigations.

The paper reports on the development of an analytical method based on the use of a new miniaturised short-wave infrared (SWIR) spectrometer for the analysis of cultural heritage samples. The spectrometer is a prototype characterised by small dimension (45.0 mm in diameter x 47.5 mm in height x 60 g weight), easily handled and transferable out of research laboratories. The prototype enables the acquisition of spectra in the SWIR range of 1200-2200 nm, which is a unique feature for miniaturised spectrometers. The exploitation of this spectral range allows the detection of a high number of combination and overtone bands, which guarantees significant diagnostic power to the instrument. The present study lays a significant foundation to the development of analytical strategies based on miniaturised NIR spectrometers working in the SWIR spectral range for the characterization of complex samples such as cultural heritage specimens. Analytical performances of the new spectrometer were assessed on archaeological bones, cinematographic films and bronze patinas. The selected cases of study present challenging conservation issues not properly addressed, and their analyses usually require to be performed on-site, in places not easily accessible by restorers, archaeologists and/or scientists. The data acquired with the prototype, combined with a multivariate data analysis approach, show the possibility to i) differentiate between the materials used as a support for cinematographic film namely cellulose nitrate (CN), cellulose acetates (CA) and polyethylene terephthalate (PET); ii) sort out archaeological bone fragments according to their collagen content as an initial screening test for bones characterization; iii) differentiate between corrosion products on outdoor bronze sculpture, which is important for assessing the state of conservation of the artwork. The prototype enabled rapid information acquisition to guide restoration strategies, which need to be supported in real time by quick and easy analytical procedures.

Rapid and direct detection of small microplastics in aquatic samples by a new near infrared hyperspectral imaging (NIR-HSI) method.

Microplastic (MP) contamination is a critical environmental challenge with a strong impact on the ecosystems, economy and potentially for human health. The smaller the MP size, the greater is the environmental risks as well as the analytical difficulties in detecting and characterising the particles. .We propose a rapid near infrared hyperspectral imaging (NIR-HSI) method that enables the chemical identification and characterisation of small MP (down to 80 µm) in aquatic samples, directly on filters, with no pre-sorting step needed. By considerably reducing the procedural steps, the time of analysis and costs our method addresses the urgent need of cost-effective and robust tools for extensive monitoring of MP in natural systems.

Do different habits affect microplastics contents in organisms? A trait-based analysis on salt marsh species.

Salt marshes in urban watersheds are prone to microplastics (MP) pollution due to their hydrological characteristics and exposure to urban runoff, but little is known about MP distributions in species from these habitats. In the current study, MP occurrence was determined in six benthic invertebrate species from salt marshes along the North Adriatic lagoons (Italy) and the Schelde estuary (Netherlands). The species represented different feeding modes and sediment localisation. 96% of the analysed specimens (330) did not contain any MP, which was consistent across different regions and sites. Suspension and facultative deposit-feeding bivalves exhibited a lower MP occurrence (0.5-3%) relative to omnivores (95%) but contained a much more variable distribution of MP sizes, shapes and polymers. The study provides indications that MP physicochemical properties and species' ecological traits could all influence MP exposure, uptake and retention in benthic organisms inhabiting European salt marsh ecosystems.

Macroscopic mid-FTIR mapping and clustering-based automated data-reduction: An advanced diagnostic tool for in situ investigations of artworks.

The present study describes a multivariate strategy that can be used for automatic on-site processing of reflection mode macro FTIR mapping (MA-rFTIR) data obtained during investigation of artworks. The chemometric strategy is based on the integration of principal component analysis (PCA) with a clustering approach in the space subtended by the three lowest-order principal components and allows to automatically identify the regions of interest (ROIs) of the area scanned and to extract the average FTIR spectra related to each ROI. Thanks to the automatic data management, in-field HSI (hyperspectral imaging)-based analyses may be performed even by staff lacking specific advanced chemometric expertise, as it is sometimes the case for conservation scientists or conservators with a scientific background. MA-rFTIR was only recently introduced in the conservation field and, in this work the technique was employed to characterize the surface of metallic artefacts. The analytical protocol was employed as part of a rapid procedure to evaluate the conservation state and the performance of cleaning methods on bronze objects. Both activities are commonly part of restoration campaigns of bronzes and require an on-site analytical procedure for efficient and effective diagnosis. The performance of the method was first evaluated on aged standard samples (bronzes with a layer of green basic copper hydroxysulphate, treated with different organic coatings) and then scrutinized in situ on areas of the 16th century Neptune fountain statue (Piazza del Nettuno, Bologna, Italy) by Gianbologna.

Microplastic in wild populations of the omnivorous crab Carcinus aestuarii: A review and a regional-scale test of extraction methods, including microfibres.

Microplastic (MP) has become ubiquitous in the marine environment. Its threat to marine organisms has been demonstrated under laboratory conditions, yet studies on wild populations still face methodological difficulties. We reviewed the methods used to separate MP from soft animal tissues and highlighted a lack of standardised methodologies, particularly critical for synthetic microfibres. We further compared enzymatic and a potassium hydroxide (KOH)-based alkaline digestion protocols on wild crabs (Carcinus aestuarii) collected from three coastal lagoons in the north Adriatic Sea and on laboratory-prepared synthetic polyester (PES) of different colour and polypropylene (PP). We compared the cost-effectiveness of the two methods, together with the potential for adverse quantitative or qualitative effects on MP that could alter the capability of the polymers to be recognised via microscopic or spectroscopic techniques. Only 5.5% of the 180 examined crabs contained MP in their gastrointestinal tracts, with a notably high quantitative variability between individuals (from 1 to 117 particles per individual). All MP found was exclusively microfibres, mainly PES, with a mean length (±SE) of 0.5 ±â€¯0.03 mm. The two digestion methods provided comparable estimates on wild crabs and did not cause any visible physical or chemical alterations on laboratory-prepared microfibres treated for up to 4 days. KOH solution was faster and cheaper compared to the enzymatic extraction, involving fewer procedural steps and therefore reducing the risk of airborne contamination. With digestion times longer than 4 days, KOH caused morphological alterations of some of the PES microfibres, which did not occur with the enzymatic digestion. This suggests that KOH is effective for the digestion of small marine invertebrates or biological samples for which shorter digestion time is required, while enzymatic extraction should be considered as alternative for larger organisms or sample sizes requiring longer digestion times.

Characterization of outdoor bronze monument patinas: the potentialities of near-infrared spectroscopic analysis.

The corrosion products usually found on outdoor bronzes are generated by the interaction between the metal alloy and the atmospheric pollutants. To protect the external surface of bronzes, different organic materials (natural or synthetic) can be applied, creating over time a patina consisting of a complex mixture of inorganic and organic degraded components. The correct chemical characterization of patina constituents is fundamental to define the state of conservation of a metal artwork and address proper restoration actions. In this paper, we evaluated the potentialities of near-infrared (NIR) reflectance microscopy (4000-7500 cm-1) as complementary method to mid-infrared (MIR) analyses for the characterization of bronze patinas. Although NIR spectroscopy has been already used in the field of heritage science, its application for the characterization of bronze patinas is almost unexplored. In this paper, several corrosion products usually found on the surface of outdoor bronze sculptures were synthesized, characterized, and submitted to the NIR-MIR total reflection analysis to build up a reference spectral database. We devoted particular attention to the NIR features of copper hydroxychlorides, such as atacamite and paratacamite, which have not been studied in detail up to now. A selection of organic-based formulations, commonly used by restorers to protect the bronze surface against the outdoor aggressive environment, were also considered as references. Successively, NIR-MIR reflectance microscopy was successfully employed for the analysis of patina micro-samples collected from the bronze statues of the Neptune Fountain (sixteenth century) located in Bologna. The obtained results demonstrate the ability of NIR spectroscopy to identify organic and inorganic patina constituents, even in mixtures. In addition, the study can be considered as a proof of concept for the possible future application of the technique for in situ diagnostic campaigns on bronze sculptures.

Miniaturized Biosensors to Preserve and Monitor Cultural Heritage: from Medical to Conservation Diagnosis.

The point-of-care testing concept has been exploited to design and develop portable and cheap bioanalytical systems that can be used on-site by conservators. These systems employ lateral flow immunoassays to simultaneously detect two proteins (ovalbumin and collagen) in artworks. For an in-depth study on the application of these portable biosensors, both chemiluminescent and colorimetric detections were developed and compared in terms of sensitivity and feasibility. The chemiluminescent system displayed the best analytical performance (that is, two orders of magnitude lower limits of detection than the colorimetric system). To simplify its use, a disposable cartridge was designed ad hoc for this specific application. These results highlight the enormous potential of these inexpensive, easy-to-use, and minimally invasive diagnostic tools for conservators in the cultural heritage field.

A new integrated TLC/MU-ATR/SERS advanced approach for the identification of trace amounts of dyes in mixtures.

The present research is focused on the setting up of an advanced analytical system for the detection of synthetic dyes. The system is based on the combination of an innovative thin layer chromatography (TLC) plate coupled with enhanced infrared (MU-ATR, metal underlayer attenuated total reflection) and Surface Enhanced Raman (SERS) spectroscopy. In particular, a TLC plate made of silver iodide (AgI) applied onto a gold coated glass slide (AgI@Au) is proposed as an efficient stationary phase for the separation of dyes mixtures. The separated dyes are then identified by means of both enhanced FTIR and SERS, performed directly on the same eluted spots. The use of a mid-IR transparent inorganic salt as stationary phase coupled with the underneath gold layer avoids spectral interferences, enhancing the signal obtained from ATR analyses. At the same time, SERS spectra can be recorded as the TLC plate may act as a SERS active substrate due to the photoreduction of AgI to metallic Ag caused by the exposure to the laser during the Raman analysis. Different mixtures of synthetic dyes of known composition, widely used in dyeing processes, have been tested and the method resulted to be effective in identifying trace amounts in the order of tens nanograms. Moreover, the method has been further evaluated on a real case study represented by dyes extracted from dyed wool.

A Multivariate Methodological Workflow for the Analysis of FTIR Chemical Mapping Applied on Historic Paint Stratigraphies.

In the field of applied researches in heritage science, the use of multivariate approach is still quite limited and often chemometric results obtained are often underinterpreted. Within this scenario, the present paper is aimed at disseminating the use of suitable multivariate methodologies and proposes a procedural workflow applied on a representative group of case studies, of considerable importance for conservation purposes, as a sort of guideline on the processing and on the interpretation of this FTIR data. Initially, principal component analysis (PCA) is performed and the score values are converted into chemical maps. Successively, the brushing approach is applied, demonstrating its usefulness for a deep understanding of the relationships between the multivariate map and PC score space, as well as for the identification of the spectral bands mainly involved in the definition of each area localised within the score maps.

A follow-up on the analytical study of discolouration of the marble statues of Orsanmichele in Florence.

The research complements the complex study carried out to understand the source of brown discolourations of ten marble statues in the Church of Orsanmichele in Florence, Italy. Originally located in exterior niches, the statues were restored to reverse the extensive alterations they had undergone throughout the centuries. One of the major alterations was the application of a dark brown patina that dated just after 1789. After the statues were placed indoors, brownish discolourations started to appear on their surfaces. Cross sections were examined using FTIR mapping and immunological methods. In parallel, the pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) data already obtained from the statues' scrapings were compared with data from aged casein films applied to microscope glass slides and aged milk-treated marble. All the statues had been treated with milk-based substances before the time the bronze patina was applied. The values of temperature and illumination of the room were important factors in the ageing of organic substances and in the formation of calcium oxalates. It is likely that products of thermo-oxidation and photo-oxidation of the oils together with the oxalates caused the darkening. The marble samples corresponded to a Lunense provenance.

Immunochemical Micro Imaging Analyses for the Detection of Proteins in Artworks.

The present review is aimed at reporting on the most advanced and recent applications of immunochemical imaging techniques for the localization of proteins within complex and multilayered paint stratigraphies. Indeed, a paint sample is usually constituted by the superimposition of different layers whose characterization is fundamental in the evaluation of the state of conservation and for addressing proper restoration interventions. Immunochemical methods, which are based on the high selectivity of antigen-antibody reactions, were proposed some years ago in the field of cultural heritage. In addition to enzyme-linked immunosorbent assays for protein identification, immunochemical imaging methods have also been explored in the last decades, thanks to the possibility to localize the target analytes, thus increasing the amount of information obtained and thereby reducing the number of samples and/or analyses needed for a comprehensive characterization of the sample. In this review, chemiluminescent, spectroscopic and electrochemical imaging detection methods are discussed to illustrate potentialities and limits of advanced immunochemical imaging systems for the analysis of paint cross-sections.

Localization of proteins in paint cross-sections by scanning electrochemical microscopy as an alternative immunochemical detection technique.

The qualitative identification of proteinaceous substances, as well as their location within a complex paint stratigraphy, is one of the most challenging issues in the characterization of painting materials. Nevertheless, information on paint components represent a crucial task for studies concerning both the ancient painting techniques adopted and the state of conservation, being fundamental investigations for the selection of appropriate conservation actions. The present research was aimed at developing a new detection approach for the immunochemical localization of ovalbumin in paint cross-sections based on the use of scanning electrochemical microscopy (SECM). The immunochemical analyses were performed using an anti-ovalbumin primary antibody and a secondary antibody labelled with horseradish peroxidase (HRP). SECM measurements were performed in feedback mode using benzoquinone (BQ)/hydroquinone (H2Q) redox couple. In presence of hydrogen peroxide (H2O2), HRP catalyzes the re-oxidation of H2Q to BQ and the increment of BQ concentration in correspondence of the target protein was detected by SECM through the electrochemical reduction of the regenerated BQ at the microelectrode. Indeed, the localization of ovalbumin was possible thanks to a clear discrimination of SECM currents, achieved by the comparison of the measurements recorded before and after H2O2 administration, based on the HRP on/off approach. The method was evaluated both on samples from standard mocks-up and on a historical sample, collected from a Renaissance wood painting. The obtained results were promising, foreseeing a wider application of SECM on cultural heritage researches.