Kathryn A. Dooley

Complementary Standoff Chemical Imaging to Map and Identify Artist Materials in an Early Italian Renaissance Panel Painting

Two imaging modalities based on molecular and elemental spectroscopy were used to characterize a painting by Cosimo Tura. Visible-to-near-infrared (400-1680 nm) reflectance imaging spectroscopy (RIS) and X-ray fluorescence (XRF) imaging spectroscopy were employed to identify pigments and determine their spatial distribution with higher confidence than from either technique alone. For example, Marys red robe was modeled through the distribution of an insect-derived red lake (RIS map) and lead white (XRF lead map), rather than a layer of red lake on vermilion. The RIS image cube was also used to isolate the preparatory design by mapping the reflectance spectra associated with it. In conjunction with results from an earlier RIS study (1650-2500 nm) to map and identify the binding media, a more thorough understanding was gained of the materials and techniques used in the painting.

Van Gogh’s Irises and Roses : the contribution of chemical analyses and imaging to the assessment of color changes in the red lake pigments

Vincent van Gogh’s still lifes Irises and Roses were investigated to shed light onto the degree to which the paintings had changed, both individually and in relation to each other since they were painted, particularly in regard to the fading of the red lakes. Non-invasive techniques, including macroscopic X-ray fluorescence mapping, reflectance imaging spectroscopy, and X-radiography, were combined with microanalytical techniques in a select number of samples. The in-depth microchemical analysis was necessary to overcome the complications that arise when evaluating by non-invasive methods alone the compositions of passages with complex layering and mixing of paints. The results obtained by these two approaches were complemented by color measurements performed on paint cross-sections and on protected edges, and with historical information provided by the artist’s own descriptions, early reviews and reproductions, and the data was used to carry out digital color simulations that provided, to a certain extent, a visualization of how the paintings may have originally appeared.Graphical abstractIrises, 1890, Vincent van Gogh. The Metropolitan Museum of Art #58.187. Zn (upper right), Pb (bottom left), and Br (bottom right) distribution maps acquired by XRF imaging.

Reflectance imaging spectroscopy and synchrotron radiation X-ray fluorescence mapping used in a technical study of The Blue Room by Pablo Picasso

The existence of a portrait hidden beneath The Blue Room (1901) by Pablo Picasso prompted a comprehensive technical study of this early Blue period painting. Microanalysis of paint samples was combined with reflectance imaging spectroscopy (RIS) and synchrotron radiation X-ray fluorescence (SR-XRF) mapping to characterize the materials and structure of the paint layers and to understand the artist’s palette and use of color in both paintings. Microanalysis of paint samples provided detailed information about pigment mixtures and paint stratigraphy while the complementary data sets provided by RIS and SR-XRF yielded important information about pigment distribution in both pictures and clarified details of the underlying painting. Overall, the comprehensive study increased understanding of both pictures and added to the growing body of knowledge about Picasso’s early experimentation and evolving technique.

Standoff chemical imaging finds evidence for Jackson Pollock's selective use of alkyd and oil binding media in a famous ‘drip’ painting

Near-infrared diffuse reflectance imaging spectroscopy (NIR-RIS, 1000 to 2500 nm) was used to map the use of alkyd and oil paints in Jackson Pollocks Number 1, 1950 (Lavender Mist), one of his most important ‘drip’ or ‘poured’ paintings. Pollocks drip paintings were created by allowing the paint to “pour” from his brush/stick down onto the canvas. Prior analysis of micro-samples from drip paintings found Pollock was extensively using alkyd-resin paints by 1949 (in addition to oil) which led to a hypothesis that he selectively used alkyd and oil paints to obtain the fluid, gestural marks characteristic of his mature style. To determine where he used alkyd and oil paints in Lavender Mist, we utilized near-infrared spectral regions (1615–1850 and 1860–2200 nm) that allowed discrimination between these binding media, especially when the first derivative spectra were examined. The near-infrared image cubes were collected with a high-spectral resolution (2.8 nm sampling) hyperspectral camera. Using convex geometry-based multivariate analysis, three spectral endmembers were identified: oil, alkyd resin, and a third binder. The mapping results show oil binding medium was confined to the uppermost layers of the painting, corresponding with long, more-or-less straight, white skeins of paint. An alkyd binding medium maps to long white skeins of paint (both straight and curved), in addition to many irregular-shaped, disconnected regions of white and blue-green paint, indicating the mapped alkyd paint is below other layers. The third spectral endmember maps to an off-white paint that may be a mixture/layering of oil and alkyd media. X-Ray fluorescence imaging spectroscopy and site-specific reflectance spectroscopy (350–2500 nm) found evidence that the oil and alkyd white paints contain zinc and titanium whites. However, the oil paint likely contains the anatase mineral form of titanium dioxide, whereas the alkyd paint likely contains rutile titanium dioxide. As these pigments do not absorb near-infrared radiation, the mapping results demonstrate the ability to use NIR-RIS to map modern paint binders. Furthermore, the use of oil and alkyd paints seem to be intentional choices by Pollock: the oil because it has more body, and the alkyd because it is more fluid and dries more quickly.

Macroscale multimodal imaging reveals ancient painting production technology and the vogue in Greco-Roman Egypt

Macroscale multimodal chemical imaging combining hyperspectral diffuse reflectance (400–2500 nm), luminescence (400–1000 nm), and X-ray fluorescence (XRF, 2 to 25 keV) data, is uniquely equipped for noninvasive characterization of heterogeneous complex systems such as paintings. Here we present the first application of multimodal chemical imaging to analyze the production technology of an 1,800-year-old painting and one of the oldest surviving encaustic (“burned in”) paintings in the world. Co-registration of the data cubes from these three hyperspectral imaging modalities enabled the comparison of reflectance, luminescence, and XRF spectra at each pixel in the image for the entire painting. By comparing the molecular and elemental spectral signatures at each pixel, this fusion of the data allowed for a more thorough identification and mapping of the painting’s constituent organic and inorganic materials, revealing key information on the selection of raw materials, production sequence and the fashion aesthetics and chemical arts practiced in Egypt in the second century AD.

Separating two painting campaigns in Saul and David, attributed to Rembrandt, using macroscale reflectance and XRF imaging spectroscopies and microscale paint analysis

Late paintings of Rembrandt van Rijn (1606–1669) offer intriguing problems for both art historians and conservation scientists. In the research presented here, the key question addressed is whether observed stylistic differences in paint handling can be correlated with material differences. In Saul and David, in the collection of the Royal Picture Gallery Mauritshuis in The Hague, NL, the stylistic differences between the loose brushwork of Saul’s cloak and the more detailed depiction of his turban and the figure of David have been associated with at least two painting stages since the late 1960s, but the attribution of each stage has been debated in the art historical literature. Stylistic evaluation of the paint handling in the two stages, based on magnified surface examination, is further described here. One of the research goals was to determine whether the stylistic differences could be further differentiated with macroscale and microscale methods of material analysis. To address this, selected areas of the painting having pronounced stylistic differences were investigated with two macroscopic chemical imaging methods, X-ray fluorescence and reflectance imaging spectroscopies. The pigments used were identified and their spatial distribution was mapped. The mapping results show that the passages rendered in more detail and associated stylistically with the first painting stage, such as the orange-red color of David’s garment or the Greek key design in Saul’s turban, were painted with predominately red ochre mixed with vermilion. The regions of loose, bold brushwork, such as the orange-red slashing strokes in the interior of Saul’s cloak, associated with the second painting stage, were painted with predominately red ochre without vermilion. These macroscale imaging results were confirmed and extended with scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDX) analysis of three cross-sections taken from regions of stylistic differences associated with the two painting stages, including one sample each from the right and left sleeve of David, and one from the interior of Saul’s cloak. SEM–EDX also identified a trace component, barium sulfate, associated with the red ochre of the second stage revisions. Combining mapping information from two spectroscopic imaging methods with localized information from microscopic samples has clearly shown that the stylistic differences observed in the paint handling are affiliated with differences in the chemical composition of the paints.

Standoff Mid‐Infrared Emissive Imaging Spectroscopy for Identification and Mapping of Materials in Polychrome Objects

Microscale mid-infrared (mid-IR) imaging spectroscopy is used for the mapping of chemical functional groups. The extension to macroscale imaging requires that either the mid-IR radiation reflected off or that emitted by the object be greater than the radiation from the thermal background. Reflectance spectra can be obtained using an active IR source to increase the amount of radiation reflected off the object, but rapid heating of greater than 4 °C can occur, which is a problem for paintings. Rather than using an active source, by placing a highly reflective tube between the painting and camera and introducing a low temperature source, thermal radiation from the room can be reduced, allowing the IR radiation emitted by the painting to dominate. Thus, emissivity spectra of the object can be recovered. Using this technique, mid-IR emissivity image cubes of paintings were collected at high collection rates with a low-noise, line-scanning imaging spectrometer, which allowed pigments and paint binders to be identified and mapped.

Multispectral reflectance imaging and reflectance spectroscopy at the interface of cultural heritage research and undergraduate education: Investigating a golden age Dutch painting at the Huntington

The National Gallery of Art (NGA) has pioneered multispectral reflectance imaging systems that are powerful tools for the analysis of art works and that can be constructed for under

Mapping of egg yolk and animal skin glue paint binders in Early Renaissance paintings using near infrared reflectance imaging spectroscopy

20,000. Obtaining a dozen or more different images of a painting in different wavelength regions from 400–1000 nm enables an image cube to be constructed which can then be interrogated with remote sensing software such as ENVI. Washington and Lee University (W&L) has been working with NGA to integrate this equipment into undergraduate research and education involving cultural heritage objects at numerous museums This paper highlights powerful results obtained analyzing a 17th century Dutch painting at The Huntington Library, Art Collections, and Botanical Gardens (The Huntington) in which several remote sensing imaging and spectroscopic techniques, along with computational manipulation of the signal data, have played a crucial role in the successful analysis.