The cultural heritage community is increasingly exploring synchrotron radiation (SR) based techniques for the study of art and archaeological objects. When considering heterogeneous and complex micro-samples, such as those from paintings, the combination of different SR X-ray techniques is often exploited to overcome the intrinsic limitations and sensitivity of the single technique. Less frequently, SR X-ray analyses are combined with SR micro-photoluminescence or micro-Fourier Transform Infrared spectroscopy, which provide complementary information on the molecular composition, offering a unique integrated analysis approach. Although the spatial correlation between the maps obtained with different techniques is not straightforward due to the different volumes probed by each method, the combination of the information provides a greater understanding and insight into the paint chemistry. In this work, we discuss the advantages and disadvantages of the combination of X-ray techniques and SR-based photoluminescence through the study of two paint micro-samples taken from Pablo Picasso's Femme (1907). The painting contains two cadmium yellow paints (based on CdS): one relatively intact and one visibly degraded. SR micro-analyses demonstrated that the two Cd-yellow paints differ in terms of structure, chemical composition, and photoluminescence properties. In particular, on the basis of the combination of different SR measurements, we hypothesize that the degraded yellow is based on nanocrystalline CdS with high presence of Cd(OH)Cl. These two characteristics have enhanced the reactivity of the paint and strongly influenced its stability.

A previous preliminary study of 15th-century Venetian manuscript fragments by the Master of the Murano Gradual identified the presence of cobalt in many ultramarine blue areas, suggesting the presence of smalt. This would represent an early use of this glassy pigment in Venetian illuminated manuscripts. Whereas sampling has been used to identify smalt in 15th century paintings, only non-invasive methods can be used on manuscripts due to their small size and fragile nature. Here we investigated four non-invasive analysis techniques to identify small amounts of smalt in the presence of ultramarine, including single-point and scanning XRF spectroscopy, UV–vis-NIR-SWIR reflectance spectroscopy (FORS), Raman spectroscopy, and external reflection FT-IR spectroscopy. This was done by studying paint mock-ups of ultramarine and smalt mixtures with and without the presence of a white pigment on parchment. The results showed molecular spectroscopy techniques (reflectance, Raman, and FTIR) require at least ~ 30–40% smalt by percent mass when in the presence of ultramarine in order to detect its presence, whereas elemental XRF spectroscopy can detect cobalt (and thus infer the presence of smalt) at the ~ 1% level. To further explore the inference of smalt by XRF, additional XRF analysis was conducted to specifically look for elements associated with cobalt minerals (i.e. nickel, arsenic, bismuth, etc.). High spatial resolution XRF scanning (60–100 μm X-ray spot size) was used to look for cobalt in smalt particles which are typically larger than those of ultramarine. These two XRF analysis approaches worked well with the mock-up paint samples, and were subsequently applied to the manuscripts for which molecular spectroscopy methods yielded no unambiguous evidence for smalt. The data underscore the challenges of conclusively identifying smalt in complex paint systems when samples are not available, but do suggest that the Master of the Murano illuminated manuscript fragments contain smalt, but perhaps not in a form or amount researchers are used to seeing in paintings.

The heraldic devices found in an important missal from Renaissance Bologna, now in the collection of the J. Paul Getty Museum, are known to have been repainted during the early life of the manuscript. To clarify these stages and enable a reassessment of the missal’s history and historiography, a technical analysis of the painted escutcheons was undertaken using Scanning Macro-X-Ray Fluorescence (MA-XRF) spectroscopy. This analytical method provides distribution maps of individual chemical elements, aiding the visualization of paint surfaces that suffered loss, abrasion, or intentional defacement, or underwent interventions such as repainting or retouching. In this article, changes to the shields are more precisely documented than ever before, allowing the authors to reconsider the early provenance of a manuscript witness to the papal crisis within the Catholic Church during the final decades of the Great Western Schism.

Spectral imaging modalities, including reflectance and X-ray fluorescence, play an important role in conservation science. In reflectance hyperspectral imaging, the data are classified into areas having similar spectra and turned into labeled pigment maps using spectral features and fusing with other information. Direct classification and labeling remain challenging because many paints are intimate pigment mixtures that require a non-linear unmixing model for a robust solution. Neural networks have been successful in modeling non-linear mixtures in remote sensing with large training datasets. For paintings, however, existing spectral databases are small and do not encompass the diversity encountered. Given that painting practices are relatively consistent within schools of artistic practices, we tested the suitability of using reflectance spectra from a subgroup of well-characterized paintings to build a large database to train a one-dimensional (spectral) convolutional neural network. The labeled pigment maps produced were found to be robust within similar styles of paintings.

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.

Fiber optics reflectance spectroscopy (FORS) is commonly used to non-invasively identify madder- and cochineal-based pigments on works of art, but the significant shifts sometimes observed in the position of their diagnostic absorption features can hinder correct interpretation of the spectra. To better understand these shifts, and improve the ability to confidently identify these pigments, a systematic study was carried out to evaluate the effects of different pigment recipes and laking substrates on reflectance spectra. Sixteen different madder- and cochineal-based pigments were synthesized using historical recipes. Each pigment, painted in four different binding media (gum Arabic, linseed oil, beeswax, and egg yolk), was fully characterized by FTIR and HPLC-DAD-MS prior to FORS measurements. The results of the study showed that, in contrast to the absorption features typically used for identification, features in the first derivative transformation of the FORS spectra provided a more robust means of primary identification. In addition, once it has been identified as cochineal, the absorption features in the spectra of cochineal-based pigments could be correlated to the recipe employed, providing a possible means for inferring the method of manufacture and laking substrate from a non-invasive analysis. The results of this study were used to create a decision tree for the identification of madder and cochineal pigments based solely on FORS.

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.

After the publication of the original article [1], the authors identified two errors in Table 1.

Compositionally similar organic red colorants in the anthraquinone family, whose photodegradation can cause irreversible color and stability changes, have long been used in works of art. Different organic reds, and their multiple chromophores, suffer degradation disparately. Understanding the details of these molecules' degradation therefore provides a window into their behavior in works of art and may assist the development of improved conservation methods. According to one proposed model of photodegradation dynamics, intramolecular proton transfer provides a kinetically favored decay pathway in some photoexcited chromophores, preventing degradation-promoting electron transfer (ET). To further test this model, we measured excited state lifetimes of substituted gas-phase anthraquinones using high-level theory to explain the experimental results. The data show a general structural trend: Anthraquinones with 1,4-OH substitution are long-lived and prone to damaging ET, while excited state intramolecular proton transfers promote efficient quenching for hydroxyanthraquinones that lack this motif.

The element‐specific distribution maps generated by scanning macro‐X‐ray fluorescence (XRF) spectroscopy are providing cultural heritage researchers with information about the composition of materials present in works of art and, more importantly, unprecedented insight into the techniques employed by artists in their creation. One of the advantages of macro‐XRF scanning is that the X‐rays probe materials in subsurface layers, allowing, for example, visualizations of hidden paintings to be produced. Consequently, macro‐XRF scanning has found wide use in the study of paintings, but the high spatial resolution also makes it particularly well suited for the study of the small‐scale painted illustrations and decorative elements found in illuminated manuscripts. The preliminary drawings made by manuscript illuminators to plan a painted composition—known as underdrawings—provide evidence relating to artists' creative vision and working process but are difficult to examine because they are generally hidden under the surface paint layer. Traditionally, underdrawings in a carbon‐based medium are visualized using infrared (IR) imaging. In this study, results of the analysis of painted illuminations from medieval illuminated manuscripts demonstrate that macro‐XRF scanning can visualize underdrawings in other materials, such as iron‐gall ink, metalpoint, and pigmented inks/paints, thus serving as a useful complement to traditional IR imaging. For manuscript illuminations in bound books, this study also discusses the use of interleaving materials to reduce unwanted signals from underlying folios. The ability to reveal manuscript underdrawings will help elucidate artistic intent and workshop practice and provide a new way to examine the history of medieval drawing.

Paints based on cadmium sulfide (CdS) were popular among artists beginning in the mid-19th century. Some paint formulations are prone to degrade, discoloring and disfiguring paintings where they have been used. Pablo Picasso's Femme (Epoque des "Demoiselles d'Avignon") (1907) includes two commercial formulations of CdS: one is visibly degraded and now appears brownish yellow, while the other appears relatively intact and is vibrant yellow. This observation inspired the study reported here of the photoluminescence emission from trap states of the two CdS paints, complemented by data from multispectral imaging, X-ray fluorescence spectroscopy, micro-FTIR, and SEM-EDS. The two paints exhibit trap state emissions that differ in terms of spectrum, intensity, and decay kinetics. In the now-brownish yellow paint, trap state emission is highly favored with respect to near band edge optical recombination. This observation suggests a higher density of surface defects in the now-brownish yellow paint that promotes the surface reactivity of CdS particles and their subsequent paint degradation. CdS is a semiconductor, and surface defects in semiconductors can trap free charge carriers; this interaction becomes stronger at reduced particle size or, equivalently, with increased surface to volume ratio. Here, we speculate that the strong trap state emission in the now-brownish cadmium yellow paint is linked to the presence of CdS particles with a nanocrystalline phase, possibly resulting from a low degree of calcination during pigment synthesis. Taken together, the results presented here demonstrate how photoluminescence studies can probe surface defects in CdS paints and lead to an improved understanding of their complex degradation mechanisms.

Abstract As one of the most desired and expensive artists’ materials throughout history, there has long been interest in studying natural lapis lazuli. The traditional method of extracting the blue component, lazurite, from lapis lazuli, as outlined in Cennini’s Il Libro dell’Arte, involves a lengthy purification process: (1) finely grind the rock; (2) mix with pine rosin, gum mastic, and beeswax; (3) massage in water to collect the lazurite. Repeating the process produces several grades of the pigment, typically referred to as ultramarine blue. Here, we investigate the sulfur environment within the aluminosilicate framework of lazurite during its extraction from lapis lazuli. The sulfur XANES fingerprint from samples taken at the different stages in Cennini’s extraction method were examined. All spectra contain a strong absorption peak at 2483 eV, attributable to sulfate present in the lazurite structure. However, intensity variations appear in the broad envelope of peaks between 2470 and 2475 eV and the pre-peak at 2469.1 eV, indicating a variation in the content of trisulfur (S3−˙) radicals. By studying the effect of each step of Cennini’s process, this study elucidates the changes occurring during the extraction and the variability within different grades of the precious coloring material. The increasing application of XANES to the study of artist’s materials and works of art motivated extending the research to assess the possibility of X-ray induced damage. Direct comparison of micro-focused and unfocused beam experiments suggests an increase of the S3−˙ radicals with prolonged exposure. Analysis indicates that induced damage follows first-order kinetics, providing a first assessment on the acceptable amount of radiation exposure to define the optimal acquisition parameters to allow safe analyses of lapis lazuli and ultramarine pigments.

Lazurite, the blue mineral found in lapis lazuli, may be a marker for the identification of provenance. Sulfur K-edge X-ray absorption near edge structure spectroscopy (XANES) of lazurite from lapis lazuli of various locations, such as Afghanistan, Russia, Chile, the USA, Iran, Tajikistan, and Myanmar, is described. The XANES spectra reveal that several different sulfur chemistries exist within lazurite, attributed to contributions from multiple sulfur species. A peak at 2482.5eV is attributed to sulfate; an envelope of peaks between 2470 and 2475eV is attributed to polysulfide radicals, polysulfide dianions, neutral sulfur, and/or thiosulfate; and a peak at 2469.1eV is attributed to the trisulfur and/or disulfur radical(s). Also, a peak of unknown origin arises at 2466.3eV in several spectra. The spectral profile for the envelope of peaks (2470 to 2475eV) varies between samples and in some instances, within a sample. Most notably, the studied samples from Chile display two distinct peaks near 2471.7 and 2473.5eV with a local minimum at 2472.5eV, unlike the most commonly observed pattern—that typically observed for samples from Afghanistan—with a single maximum intensity near 2472.5eV. Other more subtle variations in this energy range also correlate with provenance at varying degrees.

Correction for ‘Sub-micron proximal probe thermal desorption and laser mass spectrometry on painting cross-sections’ by Shawn C. Owens et al., Anal. Methods, 2014, 6, 8940–8945.

We demonstrate sub-micron, atomic force microscopy (AFM) proximal probe desorption of organic dyes, and subsequent detection via laser mass spectrometry. A nanothermal analysis (nano-TA) probe tip in contact with a surface is heated (10 000 C s ) to induce thermal desorption, creating depression sizes ranging from 360–1500 nm in diameter and 20–100 nm in depth. Desorbed material is drawn through a heated capillary via vacuum, and deposits onto a graphite sample bar. Laser desorption, followed by supersonic jet-cooling and either resonant two-photon ionization (R2PI) or non-resonant ionization mass spectrometry is used to characterize the transferred material. Individual, microscopic layers of organic dyes within painting cross-sections were successfully analyzed using this new approach. Separating the AFM thermal desorption step from the detection step allows for the use of analytical techniques appropriate for individual samples of material, desorbed with high spatial resolution.

Cross-sections containing organic dyes are used to demonstrate sub-micron atomic force microscopy thermal desorption (AFM-TD), followed by laser mass spectrometry.

Journal Article Nanometer-Scale Proximal Probe Thermal Desorption Coupled with Laser Mass Spectrometry Get access Shawn C Owens, Shawn C Owens University of California Santa Barbara, Department of Chemistry and Biochemistry, Santa Barbara, CA, USA Search for other works by this author on: Oxford Academic Google Scholar Jacob Berenbeim, Jacob Berenbeim University of California Santa Barbara, Department of Chemistry and Biochemistry, Santa Barbara, CA, USA Search for other works by this author on: Oxford Academic Google Scholar MS de Vries, MS de Vries University of California Santa Barbara, Department of Chemistry and Biochemistry, Santa Barbara, CA, USA Search for other works by this author on: Oxford Academic Google Scholar Catherine Schmidt Patterson, Catherine Schmidt Patterson Getty Conservation Institute, Los Angeles, CA, USA Search for other works by this author on: Oxford Academic Google Scholar Eoghan Dillon Eoghan Dillon Anasys Instruments, Santa Barbara, CA, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 20, Issue S3, 1 August 2014, Pages 2032–2033, https://doi.org/10.1017/S1431927614011891 Published: 27 August 2014

Since antiquity, lapis lazuli has been highly valued across many cultures for its bright blue color. Due to the material’s significance, there has long been interest in understanding its color variations and determining its geographic origin, whether used as the processed pigment ultramarine in painted works of art (e.g. paintings and manuscripts) or the raw lapis lazuli stone in cultural heritage objects (e.g. jewelry and inlaid decorations). While the most well-known source of lapis lazuli is Afghanistan, there are several other sources, including sites in Tajikistan, Iran, Russia, Canada, and Chile. Naturally occurring lapis lazuli contains the blue mineral lazurite (Na6Ca2(Al6Si6O24)(SO4,S3,S2,Cl,OH)2) with a variety of accessory minerals that are common to many of the known geological deposits—e.g. hauyne (Na3Ca(Si3Al3)O12(SO4)), pyrite (FeS2), calcium carbonate (CaCO3), and diopside (MgCaSi2O6). Much of the current research on the provenance of lapis lazuli has focused on the spectroscopic characteristics, the composition, and the overall distribution of the accessory minerals within the whole rock [1-4]. For example, work in our laboratory has shown that diopside inclusions in lapis lazuli sometimes have a fluorescent response to infrared wavelengths which may be characteristic of the geological deposit [5]. One challenge with basing provenance on the composition and distribution of accessory minerals is that the accessory minerals are mostly removed during the production of the ultramarine pigment, a process that requires crushing, sorting, and soaking the rock in an alkaline solution. Thus, a technique that focuses on in-situ analysis of the lazurite mineral alone, which remains chemically unaltered during this intensive processing, is desirable. Expanding on our previous work, this study therefore focuses on the lazurite component of lapis lazuli.