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.
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 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.
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.
Behind the Shield Turner, Nancy K.; Patterson, Catherine M. Schmidt; Keene, Bryan C.
Getty research journal,
01/2021, Letnik:
13, Številka:
13
Journal Article
Recenzirano
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.
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 size, shape, and application techniques of gold leaf in fourteenth- and fifteenth-century gold ground panel paintings attributed to artists working in Florence, Siena, and Fabriano was directly ...visualized using in situ scanning macro X-ray fluorescence spectroscopy (MA-XRF). The resulting gold (Au) Lα (9.712 keV) element distribution maps are of sufficient spatial resolution to enable an accurate and reproducible measurement of the shape and size of individual gold leaves. The resulting leaf measurements are discussed in the context of historical guild regulations, in particular, the 1403 reforms to the statutes of the Florentine Guild of Doctors and Apothecaries (
Arte dei medici e speziale
), which standardized the dimensions of gold leaf produced in Florence. The dimensions of the gold leaf from Florentine paintings created before and after the 1403 reforms were compared to each other as well as to gold ground paintings created in Siena and Fabriano. The results revealed the gold leaf squares in fourteenth-century Florentine and Sienese panels had side lengths averaging about 8 cm. In contrast, the gold leaf squares used in the fifteenth-century Florentine and Sienese paintings were smaller, with side lengths measuring about 7 cm. In addition, the degree of overlap between adjacent gold leaves was also measured. The amount of overlap was found to vary between artists, and the degree of overlap was consistent within the oeuvre of a specific artist. Taken together, these results suggest that the dimensions of the gold leaves found in panel paintings relate to the place of production on the Italian peninsula and the period in which they were created, while the degree of overlap relates to the individual hand of a gilder or artist/workshop.
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.
•Thirty-eight samples of lapis lazuli from around the world are studied.•Sulfur chemistry within lazurite is investigated with sulfur K-edge XANES.•The trisulfur radical and neutral sulfur account for major differences in the spectra.•Variation in XANES spectra potentially correlates to the provenance of lapis lazuli.
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