Characterization of lapis lazuli and corresponding purified pigments for a provenance study of ultramarine pigments used in works of art

A Study on the Materials Used in Ancient Wooden Architectural Paintings at DaZhong Gate in Confucius Temple, Qufu, Shandong, China

This study analyzes the pigments and binders used in the painted wooden structure of DaZhong Gate in the Confucius Temple in Qufu, Shandong Province, China. Five samples were collected from the building and analyzed using techniques such as polarized light microscopy (PLM), energy-dispersive X-ray spectroscopy (EDX), micro-Raman spectroscopy (m-RS), and Fourier-transform infrared spectroscopy (FT-IR). The findings reveal that the red, yellow, green, and blue pigments are identified as lead red, lead chromate yellow, emerald green, and ultramarine, respectively. The white pigment is determined to be a combination of chalk and lead white or anglesite. Considering the production period of the yellow and green pigments, it is inferred that architectural paintings underwent restoration or repainting during the late Qing Dynasty. The analysis of the binder in the pigment using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) reveals that the binder employed is a protein-based glue. Additionally, the detected presence of Heat-bodied tung oil suggests a potential connection to traditional Chinese painting techniques on wooden surfaces. This discovery not only contributes to the historical research of the Confucius Temple but also provides crucial data for the conservation and restoration efforts of this culturally significant heritage site.

Multisensor hyperspectral imaging approach for the microchemical analysis of ultramarine blue pigments

This work presents a multisensor hyperspectral approach for the characterization of ultramarine blue, a valuable historical pigment, at the microscopic scale combining the information of four analytical techniques at the elemental and molecular levels. The hyperspectral images collected were combined in a single hypercube, where the pixels of the various spectral components are aligned on top of each other. Selected spectral descriptors have been defined to reduce data dimensionality before applying unsupervised chemometric data analysis approaches. Lazurite, responsible for the blue color of the pigment, was detected as the major mineral phase present in synthetic and good quality pigments. Impurities like pyrite were detected in lower quality samples, although the clear identification of other mineral phases with silicate basis was more difficult. There is no correlation between the spatial distribution of the bands arising in the Raman spectra of natural samples in the region 1200-1850 cm-1 and any of the transition metals or rare earth elements (REE). With this information, the previous hypothesis (based on bulk analysis) attributing these bands to luminescence emissions due to impurities of these elements must be revised. We propose the consideration of CO2 molecules trapped in the cages of the aluminosilicate structure of sodalite-type. Additionally, correlation between certain Raman features and the combined presence of Ca, P, and REE, in particular Nd, was detected for the lowest quality pigment. Our results highlight the usefulness of fusing chemical images obtained via different imaging techniques to obtain relevant information on chemical structure and properties.

Revealing Artists’ Collaboration in a 14th Century Manuscript by Non-Invasive Analyses

In the last decades, the working methods of late medieval illuminators have been widely discussed by art historians and codicologists. Non-invasive analyses are able to characterise the painting methods of illuminators as well as investigate artistic collaborations among them. The aim of this study was to characterise the painting palettes and techniques of different artists who illuminated two leaves from an early fourteenth century manuscript. The analyses were carried out with non-invasive and portable techniques such as Energy Dispersive X-ray Fluorescence (ED-XRF) spectrometry, Fiber Optics Reflectance Spectroscopy (FORS) and Raman spectroscopy. The paper highlights the differences among three rich and varied palettes and examines the pigments ultramarine, azurite, verdigris, earths, orpiment, red lead, vermillion, lead white, yellow lake, indigo, brazilwood and lac, used independently or in mixtures. We have demonstrated the effectiveness of non-invasive analyses as a tool to differentiate hands of artists who have worked on the same page. Furthermore, the comparison with analyses carried out on leaves attributed to the workshop of Pacino di Bonaguida allows to investigate in-depth the production of the main illuminators active in Florence at the dawn of the Renaissance.

Investigations of byzantine wall paintings in the abbey of Santa Maria di Cerrate (Italy) in view of their restoration

In this paper, diagnostic analyses on 12th-13th century byzantine wall paintings in the abbey of Santa Maria di Cerrate (Southern Italy) were carried out preparatory to restoration work promoted by FAI (Fondo Ambiente Italiano). Both the pigments and the areas with a bleaching alteration in the frescoes were analysed using the energy dispersive X-ray fluorescence, the Raman spectroscopy and the scanning electron microscopy equipped with energy dispersive X-ray spectrometer. In particular, ED-XRF analyses were performed in situ on wall paintings, while Raman spectroscopy and SEM-EDX were accomplished on frescoes fragments. The results obtained allowed to determine the chemical composition of the pigments, helping to identify the original parts of the frescoes from the retouched ones. The work also provided important information about the historical-artistic context of the abbey. Archaeometric investigations have indeed revealed the pictorial technique used for the wall paintings of the abbey, as well as the presence of some very valuable pigments, such as lapis lazuli blue.

Sulfur K-edge micro- and full-field XANES identify marker for preparation method of ultramarine pigment from lapis lazuli in historical paints

Ultramarine blue pigment, one of the most valued natural artist's pigments, historically was prepared from lapis lazuli rock following various treatments; however, little is understood about why or how to distinguish such a posteriori on paintings. X-ray absorption near-edge structure spectroscopy at the sulfur K-edge in microbeam and full-field modes (analyzed with nonnegative matrix factorization) is used to monitor the changes in the sulfur species within lazurite following one such historically relevant treatment: heating of lapis lazuli before extracting lazurite. Sulfur signatures in lazurite show dependence on the heat treatment of lapis lazuli from which it is derived. Peaks attributed to contributions from the trisulfur radical-responsible for the blue color of lazurite-increase in relative intensity with heat treatment paralleled by an intensified blue hue. Matching spectra were identified on lazurite particles from five historical paint samples, providing a marker for artists' pigments that had been extracted from heat-treated lapis lazuli.

Laboratory multi-technique study of Spanish decorated leather from the 12th to 14th centuries

This work comprises an exhaustive study of Spanish decorative leathers dating from the 12th to 14th centuries. These paintings are considered a key example of a crucible of artistic styles: Gothic, Islamic and Florentine Trecento. The goal of this work was to use the scientific information provided by a number of experimental techniques - namely EDX, micro-FTIR, micro-Raman and micro-XRD - to assess the dating of the wooden vault, leather preparation and filling fibres. Another goal was to assess the artistic technique based on the characterization of pigments and the differentiation between original materials and those added throughout its history. Gypsum was the original preparation layer extended over the leather. A new preparation stratum was added in further interventions with the artwork. The original pictorial materials and those used during refurbishments have been identified. Original pigments were: red lead, Mars red, red lake, cinnabar, lapis lazuli, red ochres, raw sienna, white lead and charcoal black. Gilding was also found. Pigments added during restoration were: barite, emerald green, rutile, anatase, Mars red, cadmium red, lithopone, cadmium yellow, charcoal black and orpiment.

From lapis lazuli to ultramarine blue: investigating Cennino Cennini’s recipe using sulfur K-edge XANES

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.

µ-XRF Analysis of Trace Elements in Lapis Lazuli-Forming Minerals for a Provenance Study

This paper presents new developments on the provenance study of lapis lazuli started by our group in 2008: during the years a multi-technique approach has been exploited to obtain minero-petrographic characterization and creation of a database considering only rock samples of known provenance. Since the final aim of the study is to develop a method to analyze archeological findings and artworks made with lapis lazuli in a completely non-invasive way, ion beam analysis techniques were employed to trace the provenance of the raw material used for the production of artifacts. Continuing this goal and focusing the analysis on determination of more significant minero-chemical markers for the provenance study of trace elements in different minerals, the method was extended with the use of micro X-ray fluorescence (µ-XRF), to test the potential of the technique for this application. The analyzes were focused on diopside and pyrite in lapis lazuli samples of known provenance (Afghanistan, Tajikistan, and Siberia). In addition, µ-XRF data were compared with micro proton-induced X-ray emission (µ-PIXE) results to verify the agreement between the two databases and to compare the analytical performance of both techniques for this application.

Rheoreversible hydrogels in paper restoration processes: a versatile tool

BACKGROUND

Paper based artworks are probably ones of the most difficult materials to restore, because of their complexity and fragile structure. Cleaning of paper artifacts, one of the process commonly carried out during restoration, usually involves the use of solvents (organic or not), that may cause several troubles, like swelling and dissolution of some components, and may also be harmful to the users.

RESULTS

Innovative procedure for cleaning paper artworks is reported in this paper. It is based on the use of rheoreversible, biocompatible hydrogels containing poly(ethylene oxide) or poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) and α-cyclodextrin. We have studied two types of polymer with different hydrophobic properties in order to obtain two different hydrogels with slightly different cleaning capabilities. Our overall strategy has been to develop innovative systems based on these hydrogels so as to better confront the problems that a restorer faces during the cleaning of paper samples. Rheoreversible hydrogels are intriguing materials because their application and removal is not invasive and does not require a liquid treatment that could induce damage to the paper.

CONCLUSIONS

These hydrogels have been applied in the cleaning of both new and aged paper samples and their cleaning efficiency has been established. Moreover, by comparison with traditional methods, the greater efficacy of the proposed procedure has been demonstrated.To assess the cleaning efficacy of these hydrogels, a multidisciplinary approach, combining non-invasive spectroscopic infrared techniques together with scanning electron microscopy, chromatographic (HPLC) analysis and pH investigations has been used. Near infrared spectroscopy spectra were coupled with a chemometric analysis to achieve a better interpretation of data.This work constitutes a preliminary step towards focused study in the development of α-cyclodextrin/polymer hydrogel family which will allow cleaning of paper artifacts with peculiar characteristics.

Analytical Raman spectroscopy in a forensic art context: the non-destructive discrimination of genuine and fake lapis lazuli

The differentiation between genuine and fake lapis lazuli specimens using Raman spectroscopy is assessed using laboratory and portable instrumentation operating at two longer wavelengths of excitation in the near-infrared, namely 1064 and 785 nm. In spite of the differences between the spectra excited here in the near infrared and those reported in the literature using visible excitation, it is clear that Raman spectroscopy at longer wavelengths can provide a means of differentiating between the fakes studied here and genuine lapis lazuli. The Raman spectra obtained from portable instrumentation can also achieve this result, which will be relevant for the verification of specimens which cannot be removed from collections and for the identification of genuine lapis lazuli inlays in, for example, complex jewellery and furniture. The non-destructive and non-contact character of the technique offers a special role for portable Raman spectroscopy in forensic art analysis.