Mobile Spectroscopic Instrumentation in Archaeometry Research

MACHINA, the Movable Accelerator for Cultural Heritage In-situ Non-destructive Analysis: project overview

Over the years, transportable instrumentation for cultural heritage (CH) in situ measurements has noticeably widespread, due to logistic, economical and safety reasons. Ion beam analysis, a powerful set of analytical techniques, of great importance for CH, is instead carried out by using fixed instrumentation. To overcome this limit, the Italian national Institute of Nuclear Physics (INFN), CERN (European Centre for Nuclear Research) and the Opificio delle Pietre Dure (OPD), started MACHINA, the “Movable Accelerator for CH In-situ Non-destructive Analysis: the new generation of accelerators for art” to build a transportable accelerator, compact, with strongly reduced weight, absorbed power and cost. MACHINA will be installed at the OPD and dedicated to CH. It will be moved to major conservation centres and museums, when needed. The INFN-CERN proposal, approved in December 2017, became operative in February 2018. 2018 was dedicated to the acquisition of material/instrumentations, to set up both a dummy accelerator (to test the vacuum system) and a vacuum chamber (to test the source). Due to COVID, in 2020 and 2021 the experimental work was slowed down, but we kept developing the control electronics/software and built the second-generation supporting structure. The HF-RFQ power supplies were integrated in October 2021. At the rise of 2022, after conditioning the cavities, we tested the system and in March 2022 we got the first extracted 2-MeV proton beam. In this paper, we present the structure of the MACHINA system, the approach followed and the main solutions adopted, with a special focus on the control system, and finally the first experimental results.

Palmyrene Polychromy: Investigations of Funerary Portraits from Palmyra in the Collections of the Ny Carlsberg Glyptotek, Copenhagen

The current study is the first comprehensive investigation of the polychromy of Palmyrene funerary portraits. It presents the technical examinations of six portraits (ca. 150–250 CE) from the collection of the Ny Carlsberg Glyptotek, illustrating the marvellous splendour of the cultural heritage of ancient Palmyra. The six portraits were examined with various analytical methods, including microscopy, ultraviolet-induced visible fluorescence imaging and visible light-induced infrared luminescence imaging, X-ray fluorescence spectroscopy, scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. Finally, two samples were collected for liquid chromatography–tandem mass spectrometry to obtain the amino acid sequence information. Various pigments were detected in the polychromy including lapis lazuli, pyromorphite, mimetite, yellow ochre, red ochre, a red lake, lead carbonate, zinc oxide, bone black, and charcoal black. The proteinaceous binding medium was identified as collagen-based and possibly also keratin-based animal glue. The examinations of the Palmyrene portraits in the Ny Carlsberg Glyptotek have proven that these artefacts, despite their current uniform, white appearance, originally presented themselves in a wealth of colours. This is illustrated by the digital reconstructions carried out of two of the examined portraits, which show how the original painting of these portraits would have given them an entirely different expression from what we see today.

Raman Spectroscopy Analysis of the Mural Pigments in Lam Rim Hall of Wudang Lamasery, Baotou Area, Inner Mongolia, China

This paper presents scientific analyses of the wall paintings in Wudang Lamasery, which is located in the Baotou area of Inner Mongolia, China. Raman spectroscopy was used to analyze the pigments of the mural of the Lam rim Hall. The results show that vermilion, red lead, chrome yellow, emerald green and synthetic ultramarine were used. The existence of synthetic pigments provides a clue for the date the mural was painted.

Architectural Polychromy on the Athenian Acropolis: An In Situ Non-Invasive Analytical Investigation of the Colour Remains

The preservation of the Athenian Acropolis monuments constitutes an ongoing top-priority national project of global significance and impact. The project concerning the analytical investigation of the polychromy of the Acropolis monuments presented in this paper was part of the Acropolis Restoration Service (YSMA) program (2011–2015), regarding the restoration of the two corners of the west entablature of the Parthenon, which exhibited severe static damage, and a parallel restoration program of the Propylaea. The scope of this research was to investigate the materials in the paint decoration remains on the monuments by applying, entirely in situ, numerous non-invasive techniques on selected architectural members of the Parthenon and the Propylaea. The research focused, mainly, on surfaces where traces of colour or decoration patterns were visible to the naked eye. Furthermore, surfaces that are referred to in the literature as decorated but that are currently covered with weathering crusts (of white or black colour) and/or layers of patina (of yellowish and orange-brown hue), were also examined. The techniques applied in situ on the Acropolis monuments were X-ray fluorescence, micro-Raman, and Fourier Transform InfraRed (FTIR) spectroscopic techniques, conducted with the use of handheld or portable instruments. The scientific data gathered in situ are discussed in this paper to enhance our knowledge of the architectural polychromy of the classical period. Further investigation by applying analytical techniques on a few selected micro-samples would be highly complementary to this present work.

Characterization of Wall Paintings of the Harem Court in the Alhambra Monumental Ensemble: Advantages and Limitations of In Situ Analysis

Non-invasive techniques (X-ray fluorescence, XRF, and Raman spectroscopy) were used for the study of the Hispano Muslim wall paintings. Principal component analysis (PCA) was performed on the semi-quantitative XRF results directly provided by the in-built factory calibrations with minimum user manipulation. The results obtained were satisfactory and highlighted differences and similarities among the measurement points. In this way, it was possible to differentiate the decorations carried out on gypsum plasterwork and the wall paintings over lime plaster. The color palette, revealed by combining the results from XRF and Raman spectroscopies, comprised the pigments hematite, lapis lazuli, cinnabar (in poor conservation state), and possibly, carbon. Evidence of past interventions was also provided by PCA on XRF data, which detected the presence of Pb, Ba, and Zn in some areas. Furthermore, the preparation layers have been studied in detail on cross-sections of two microsamples. Several layers of lime plaster with a compact microstructure have been observed. The characteristic of the pictorial layer and the identification of calcium oxalate point to the use of a secco-technique. The main alteration identified was a gypsum surface layer covering the painting and signs of plaster deterioration due to gypsum migration to more internal areas. Finally, the comparison with the observations made by restorers in previous interventions on these paintings revealed the importance of the representativeness gained with the in situ study, which enabled the analysis of a high number of areas.

Influence of surface roughness on the spectroscopic characterization of jadeite and greenstones archaeological artifacts: The axe-god pendants case study

Spectroscopic techniques are commonly used for the non-invasive characterization of the molecular and elemental composition of greenstone archaeological artifacts. The surface topography of these artifacts is greatly influenced by the crafting and polishing techniques employed in their making. However, no study of the effect of roughness on spectra has ever been reported for greenstones. Here we show that infrared, Raman and X-ray fluorescence spectra are strongly influenced by the sample's surface roughness. Spectral changes were seen in both geological (45 jadeite and green stone samples) and archaeological artifacts (12 axe-God pendants); in every case, the variations were more prominent in samples with higher arithmetic average height values. The results show that these changes can affect the interpretation of the spectroscopic data and limit the efficacy of statistical analysis. Consequently, any spectroscopic characterization of this type of samples should be performed preferably in areas with lower values of roughness parameters. Overall, FT-IR appears to be the most advantageous technique to distinguish the differences in mineral composition of this type of samples during in situ studies; its performance was evaluated with an innovative statistical analysis that treats the spectra as functional data. Additionally, the results suggest that confocal Raman spectroscopy is an ideal complementary technique that enhances mineralogical characterization, nevertheless its applicability is limited to laboratory settings.

Multi-Technique Diagnostic Analysis of Plasters and Mortars from the Church of the Annunciation (Tortorici, Sicily)

Plasters and mortars of the Church of the Annunciation (Tortorici, Sicily) were characterized, for the first time, both at the elemental and molecular levels, by means of portable X-ray fluorescence (XRF) and Raman spectroscopy, to achieve information on the “state of health” of the whole structure. The understanding of their degradation mechanisms and the identification of consequent degradation patterns can define the environmental factors responsible for interpreting the potential pathological forms that can impact the general building vulnerability. In this sense, the results obtained in this article provide relevant information to identify and address both the characterization of building materials and the fundamental causes of their deterioration. At the same time, if coupled with the attempt to supply a chronological order of the major restoration interventions carried out on the investigated site, they provide new insights to calibrate the models for building vulnerability studies.

Synchrotron X-ray Microprobes: An Application on Ancient Ceramics

Synchrotron X-ray µ- and nano-probes are increasingly affirming their relevance in cultural heritage applications, especially in material characterization of tiny and complex micro-samples which are typical from archaeological and artistic artifacts. For such purposes, synchrotron radiation facilities are tailoring and optimizing beamlines and set-ups for CH, taking also advantages from the challenges offered by the third-generation radiation sources. In ancient ceramics studies, relevant information for the identification of production centers and manufacture technology can be obtained in a non-invasive and non-destructive way at the micro-sample level by combining different SR based methods. However, the selection of appropriate beamlines, techniques and set-ups are critical for the success of the experiments. Fine and varnished wares (e.g., Attic and western-Greek colonial products) are an excellent case study for exploring challenges offered by synchrotron X-ray microprobes optimized to collect microchemical and phase-distribution maps. The determination of provenance and/or technological tracers is relevant in correctly classifying productions, often based only on ceramic paste, gloss macroscopic features or style. In addition, when these vessels are preserved in Museums as masterpieces or intact pieces the application of non-invasive approach at the micro sample is strictly required. Well-designed synchrotron µXRF and µXANES mapping experiments are able providing relevant clues for discriminating workshops and exploring technological aspects, which are fundamental in answering the current archaeological questions on varnished Greek or western-Greek colonial products.

LABEC, the INFN ion beam laboratory of nuclear techniques for environment and cultural heritage

The LABEC laboratory, the INFN ion beam laboratory of nuclear techniques for environment and cultural heritage, located in the Scientific and Technological Campus of the University of Florence in Sesto Fiorentino, started its operational activities in 2004, after INFN decided in 2001 to provide our applied nuclear physics group with a large laboratory dedicated to applications of accelerator-related analytical techniques, based on a new 3 MV Tandetron accelerator. The new accelerator greatly improved the performance of existing Ion Beam Analysis (IBA) applications (for which we were using since the 1980s an old single-ended Van de Graaff accelerator) and in addition allowed to start a novel activity of Accelerator Mass Spectrometry (AMS), in particular for ¹⁴C dating. Switching between IBA and AMS operation became very easy and fast, which allowed us high flexibility in programming the activities, mainly focused on studies of cultural heritage and atmospheric aerosol composition, but including also applications to biology, geology, material science and forensics, ion implantation, tests of radiation damage to components, detector performance tests and low-energy nuclear physics. This paper describes the facilities presently available in the LABEC laboratory, their technical features and some success stories of recent applications.

Parchments and coloring materials in two IXth century manuscripts: On-site non-invasive multi-techniques investigation

One among the most famous ancient parchments in the Islamic world, dating back to the IXth century, along with another contemporary one have been investigated by means of a completely non-invasive multi-techniques analysis combining all of elemental XRF and structural/molecular Raman, ATR-FTIR and FOR spectroscopies besides pHs and colorimetric measurements. The materials initially used in the preparation of the writing supports were identified; in addition to calcite at different extents, the parchments seem to be condensed tannins-pretreated. Furthermore, the exploration of amide I and II vibrational bands and sub-bands illustrated collagen gelatinization and molecular helix disorders phenomena. Parchments and inks degradation products, gypsum and calcium oxalates, have been also identified. In both manuscripts the writing black inks have been characterized as iron gall type. The corrosive effect of these black inks appears deeply damaging the acidic parchment supports. In this case, the high frequency side of the infrared spectrum disappears completely, illustrating thus irreversible parchment degradations. Gum Arabic, when added sufficiently in the black ink recipe, seems preventing the corrosive damaging effect induced by Fe²⁺ ions spreading from the black ink into the parchment body. Besides, all coloring materials have been identified; gold in gilded scriptures and natural pigments for vocalizations and basic decorations: cinnabar for reds, lapis-lazuli for blue and orpiment/realgar/pararealgar arsenic sulfides for yellow/orange shades. The anthraquinone-based kermesic acid extracted from Kermes female insects had been used for dark pink decorations, while the copper-based pigment verdigris had been synthetized to achieve green motifs. These results enrich the knowledge of ancient writing supports and materials, and highlight technologies and practices developed by middle-ages craftsmen.

The Irreplaceable Contribution of Cross Sections Investigation: Painted Plasters from the Sphinx Room (Domus Aurea, Rome)

Fragments and micro-fragments of painted plasters from the Sphinx Room, recently discovered in the Domus Aurea Esquiline wing (Rome, Italy), were studied. They were respectively taken from the debris in the vicinity of the walls and from already damaged edges of the decorated walls. A previous study, mainly based on non-destructive and non-invasive investigations, proved effective in giving a general overview of the employed palette, allowing the comparison with paintings from the same palace and other coeval contexts, and also providing some preliminary hints concerning the pictorial technique. Nevertheless, some issues remained unsolved, concerning the pigment mixtures (e.g., lead-/iron-based yellow to red colors; copper-/iron-based green/greyish areas), and the a fresco/a secco painting technique debate. Therefore, cross sections of the above-mentioned fragments were observed by means of Optical (OM) and Scanning Electron (SEM) Microscopy and analyzed with micro-Raman spectroscopy and Energy Dispersive X-Ray Spectroscopy (EDS), with the aims of: studying the paint layer composition through point analysis and mapping of the elemental distribution; comparing these in relation to what was observed with previously reported non-destructive analyses; studying the stratigraphy of the painted plaster, focusing on the contact between the plaster and the paint.

Handheld X-ray Fluorescence (XRF) Versus Wavelength Dispersive XRF: Characterization of Chinese Blue-and-White Porcelain Sherds Using Handheld and Laboratory-Type XRF Instruments

Almost all archaeometric studies on Chinese ceramics are carried out on the excavation materials. Therefore, a detailed, comparable database that defines different workshops and production periods already exists. But the masterpieces preserved at museums, art galleries, and/or private collections, which are artistically considered as genuine artifacts, also require similar scientific investigations to define their provenance and authenticity. The research on artworks is only possible with the use of portable, noninvasive techniques that are developing daily concerning their capability of detection limits, rate of measurement, and ease of use. In this study, the results obtained with a handheld X-ray fluorescence (XRF) (also called portable XRF) and wavelength dispersive XRF instrument were compared to evidence the efficiency and drawbacks of the portable model. To achieve this goal, 12 sherds, which represent blue-and-white porcelains of Yuan and Ming Dynasties (China), were analyzed and the chemical composition of the body, glaze, and blue decor were identified. The comparison of the results with the measurements carried out on the excavation materials, which are produced in both southern and northern China, revealed the authenticity of the artifacts. Even sodium cannot be detected with portable XRF, the distinction of different production centers is possible with the detection of major (Mg, Al, Si, K, Ca), minor (Fe, Ti), and trace elements (Zr, Sr, Rb).

Non-Invasive Investigation of Pigments of Wall Painting in S. Maria Delle Palate di Tusa (Messina, Italy)

The characterization of materials used in the archaeological field needs an experimental approach in order to avoid the destruction or perturbation of artworks. In order to afford this purpose, a multi-analytical spectroscopic approach is regularly used. We combined non-invasive analysis by using handheld spectroscopic instrumentations (mainly XRF and Raman spectrometers) in order to characterize the wall painting preserved in the church of S. Maria delle Palate at Halaesa Arconidea archeological site (Tusa, Messina, Italy). The aim of the work is the characterization of the nature of pigments used for the realization of the wall painting. The wall painting, probably representing St. Francis in the act of receiving the stigmata, has been subject to cleaning and restoration. Thanks to use of in situ measurement, we have identified hematite and goethite for the red and yellow respectively, and lazurite for the blue. In addition, some relevant information about the black pigment, the technique used for the realization and the conservation state were also obtained. The results obtained during the diagnostic campaign have been a support for the work of restorers. For the first time, the wall painting has been studied, increasing the knowledge of Halaesa Arconidea archaeological site.

Combined 3D Surveying and Raman Spectroscopy Techniques on Artifacts Preserved at Archaeological Museum of Lipari

Over the last years, the documentation of Heritage has been increasingly enriched with new forms of data representation and contents deriving from technological applications on artifacts and the progress of computer graphics: if, on the one hand, 3D survey has become an effective tool supplementing and supporting traditional study activities, as it can generate accurate and high-resolution digital models (available especially when physical access to materials is not possible, but also for enhancement or to formulate hypothetic reconstruction), on the other, archaeometry investigations can provide all that information (about composition, firing temperature of clay, etc.) that autopsy, comparison, formal, contextual, or bibliographic analysis cannot do on their own.

Portable Spectroscopy

Until very recently, handheld spectrometers were the domain of major analytical and security instrument companies, with turnkey analyzers using spectroscopic techniques from X-ray fluorescence (XRF) for elemental analysis (metals), to Raman, mid-infrared, and near-infrared (NIR) for molecular analysis (mostly organics). However, the past few years have seen rapid changes in this landscape with the introduction of handheld laser-induced breakdown spectroscopy (LIBS), smartphone spectroscopy focusing on medical diagnostics for low-resource areas, commercial engines that a variety of companies can build up into products, hyphenated or dual technology instruments, low-cost visible-shortwave NIR instruments selling directly to the public, and, most recently, portable hyperspectral imaging instruments. Successful handheld instruments are designed to give answers to non-scientist operators; therefore, their developers have put extensive resources into reliable identification algorithms, spectroscopic libraries or databases, and qualitative and quantitative calibrations. As spectroscopic instruments become smaller and lower cost, "engines" have emerged, leading to the possibility of being incorporated in consumer devices and smart appliances, part of the Internet of Things (IOT). This review outlines the technologies used in portable spectroscopy, discusses their applications, both qualitative and quantitative, and how instrument developers and vendors have approached giving actionable answers to non-scientists. It outlines concerns on crowdsourced data, especially for heterogeneous samples, and finally looks towards the future in areas like IOT, emerging technologies for instruments, and portable hyphenated and hyperspectral instruments.

Archaeological investigations (archaeometry)

Archaeometry is the research area on the edge between humanities and natural sciences: it uses and optimises methods from chemistry, spectroscopy, physics, biology, etc. to help answering research questions from humanities. In general, these objects are investigated for several reasons. Besides the fundamental interest to know about the materials that were used in the past, the study of artefacts can support their preservation, either by helping to select optimal storage or display conditions, either by investigating decay pathways and suggesting solutions. Other reasons for art analysis include provenance studies, dating the artefact or identifying forgeries. Since several years, Raman spectroscopy is increasingly applied for the investigation of objects of art or archaeology. The technique is well-appreciated for the limited (or even absent) sample preparation, the relative straightforward interpretation of the spectra (by fingerprinting - comparing them against a database of reference pigments) and its speed of analysis. Moreover, the small spectral footprint – allowing to record a molecular spectrum of particles down to 1 µm, the typical size of pigment grains – is certainly a positive property of the technique. Raman spectroscopy can be considered as rather versatile, as inorganic as well as organic materials can be studied, and as the technique can gather information on crystalline as well as on non-crystalline phases. As a consequence, Raman spectroscopy can be used to study antique objects and twentieth-century synthetic (organic) materials – illustrating the wide range of applications. Finally, the technique is as non-destructive, provided the laser power is kept sufficiently low not to damage the artwork. In literature, the terms “non-invasive” and “non-destructive” are used, where the first term means that no sampling is involved, and the latter term indicates that no sample is taken or that during analysis the sample is not consumed (destroyed) and remains available for further analysis.

The Danger of Relying on Database Spectra

With the availability of easy-to-use commercial instrumentation for infrared (IR) and Raman spectroscopy, the number of users is growing very fast. Even in labs in which no personnel with experience in spectroscopy is around, spectra can be recorded and analyzed. However, for an inexperienced person it is virtually impossible to check whether a spectrum is plausible. In this Note, it is demonstrated that even comparing an experimental spectrum with data from a database may lead to significant errors. The vibrational spectrum of dimethyl sulfoxide (DMSO) is presented as an example.

In situ Raman mapping of art objects

Raman spectroscopy has grown to be one of the techniques of interest for the investigation of art objects. The approach has several advantageous properties, and the non-destructive character of the technique allowed it to be used for in situ investigations. However, compared with laboratory approaches, it would be useful to take advantage of the small spectral footprint of the technique, and use Raman spectroscopy to study the spatial distribution of different compounds. In this work, an in situ Raman mapping system is developed to be able to relate chemical information with its spatial distribution. Challenges for the development are discussed, including the need for stable positioning and proper data treatment. To avoid focusing problems, nineteenth century porcelain cards are used to test the system. This work focuses mainly on the post-processing of the large dataset which consists of four steps: (i) importing the data into the software; (ii) visualization of the dataset; (iii) extraction of the variables; and (iv) creation of a Raman image. It is shown that despite the challenging task of the development of the full in situ Raman mapping system, the first steps are very promising.This article is part of the themed issue 'Raman spectroscopy in art and archaeology'.