Revealing Degas’s process and material choices in a late pastel on tracing paper with visible-to-near-infrared reflectance imaging spectroscopy

ABSTRACT

Visible-to-near-infrared reflectance imaging spectroscopy (417–2500 nm), the collection of hundreds of images in contiguous narrow spectral bands calibrated to reflectance, was employed to characterize drawing materials in Ballet Scene, a large-scale pastel on tracing paper by Edgar Degas. The spectral range from 417 to 950 nm proved useful in identifying and mapping the complex pigment application. The near-infrared (NIR) range from 962 to 2500 nm allowed visualization of underdrawing below multiple layers of pastel and fixative that depict positions of the dancers’ bodies and costumes in the pastel’s early developmental stages. This study compares the visualization of underdrawing in images gathered from reflectance imaging spectroscopy in narrow spectral bands with those obtained from infrared reflectography (IRR) in broad spectral bands, a technique widely used in the art conservation field.

Passages in which Degas explores various limb positions are better visualized with image products derived from reflectance imaging spectroscopy than broadband IRR images. For example, false-color reflectance images that display narrow NIR spectral bands were useful to separate and visualize the distribution of materials and more clearly convey Degas’s processes of compositional refinement. These results provide a deeper understanding of Degas’s working method and explore the relationship of Ballet Scene with similar works.

RÉSUMÉ

La spectroscopie d'imagerie par réflectance dans le visible proche infrarouge (417-2500nm), un assemblage de centaines d’images en bandes spectrales étroites et très rapprochées des bandes voisines, étalonnées selon la réflectance, a été utilisée pour analyser les médiums d’un pastel de grand format exécuté sur papier calque par Edgar Degas, intitulé Scène de ballet. La gamme spectrale de 417 à 950 nm s’est avérée très utile pour l’identification et l’étude de la répartition des pigments. L’examen dans le proche infrarouge, de 962 à 2500 nm, a permis de visualiser le dessin préparatoire sous plusieurs couches de pastel et de fixatif, révélant les diverses positions des corps des danseurs et des costumes dans les étapes préliminaires de création. Cette étude compare l’examen des images des esquisses obtenues par spectroscopie d’imagerie par réflectance à bandes étroites avec celui des images obtenues par la réflectographie infrarouge à larges bandes, une technique fréquemment utilisée dans le domaine de la conservation de l’art. Les images issues de la spectroscopie d’imagerie par réflectance permettent de mieux rendre visibles les zones de pastel plus denses où Degas explore des variations sur la posture des danseurs, que celles issues de la réflectographie infrarouge à larges bandes. Par exemple, la réflectance en fausses couleurs, qui présente les bandes spectrales du proche infrarouge, s’est avérée très utile pour dissocier et visualiser les matériaux employés, ce qui permet de mieux comprendre le processus de raffinement compositionnel de Degas. Ces résultats contribuent à une meilleure compréhension de la méthode de travail de Degas et mettent en parallèle la relation étroite entre la Scène de ballet et d’autres œuvres comparables. Traduit par André Bergeron.

RESUMO

Espectroscopia de imagem por refletância no infravermelho próximo ao visível (417–2500 nm), a coleção de centenas de imagens em faixas espectrais estreitas contíguas calibradas para reflectância, foi empregada para caracterizar materiais de desenho em Ballet Scene, um pastel em grande escala em papel vegetal feito por Edgar Degas. A faixa espectral de 417 a 950 nm mostrou-se útil para identificar e mapear a complexa aplicação de pigmentos. A faixa de infravermelho (NIR) de 962 a 2500 nm permitiu a visualização de um desenho escondido sob as várias camadas de pastel e fixativo que retrata posições dos corpos e figurinos dos dançarinos nos primeiros estágios de desenvolvimento do pastel. Este estudo compara a visualização do desenho escondido em imagens obtidas por espectroscopia de reflectância em bandas espectrais curtas com aquelas obtidas por reflectografia infravermelha (IRR) em bandas espectrais amplas, uma técnica amplamente utilizada no campo da conservação da arte. Locais nos quais Degas explora posições de vários membros são melhor visualizadas com produtos de imagem derivados de espectroscopia por imageamento de refletância do que imagens de IRR de banda larga. Por exemplo, imagens de refletância de cores falsas que exibem bandas espectrais NIR estreitas foram úteis para separar e visualizar a distribuição de materiais e transmitir mais claramente os processos de refinamento composicional de Degas. Estes resultados fornecem uma compreensão mais profunda do método de trabalho de Degas e exploram a relação de Ballet Scene com obras semelhantes. Traduzido por Beatriz Haspo.

RESUMEN

La espectroscopía de imágenes de reflectancia visible a infrarrojo cercano (417–2500 nm), la colección de cientos de imágenes en bandas espectrales estrechas contiguas calibradas para reflectancia, se empleó para caracterizar los materiales de dibujo en Ballet Scene, un pastel a gran escala sobre papel cebolla por Edgar Degas. El rango espectral de 417 a 950 nm resultó ser útil para identificar y mapear la aplicación compleja del pigmento. El rango de infrarrojo cercano (NIR) de 962 a 2500 nm permitió la visualización del dibujo preparatorio debajo de múltiples capas de pastel y fijador que representan las posiciones de los cuerpos y trajes de los bailarines en las primeras etapas de desarrollo del pastel. Este estudio compara la visualización de dibujos en imágenes de espectroscopía de imágenes de reflectancia en bandas espectrales estrechas con las obtenidas en reflectografía infrarroja (IRR) en bandas espectrales amplias, una técnica ampliamente utilizada en el campo de la conservación de arte. Los pasajes en los que Degas explora varias posiciones de las extremidades se visualizan mejor con productos de imagen derivados de la espectroscopia de imágenes de reflectancia que con las imágenes de IRR de banda ancha. Por ejemplo, las imágenes de reflectancia de color falso que muestran bandas espectrales NIR estrechas fueron útiles para separar y visualizar la distribución de materiales y transmitir más claramente los procesos de refinamiento de la composición de Degas. Estos resultados proporcionan una comprensión más profunda del método de trabajo.

KEYWORDS:

• Reflectance imaging spectroscopy
• infrared reflectography
• broadband
• narrow spectral band
• false-color image
• principal component image
• underdrawing
• Edgar Degas

Acknowledgments

The authors would like to extend their gratitude to the curators and conservators at the Carnegie Museum of Art for access to Dancers, Entrance on Stage. Many thanks to John K. Delaney, Suzanne Quillen Lomax, Michael Palmer, and Barbara Berrie (Scientific Research Department at the National Gallery of Art, Washington, DC) for their expertise and support throughout this project. Michelle Facini would like to thank Kimberly Schenck, Marian Dirda, and Amy Hughes (Paper Conservation Department at the National Gallery of Art, Washington, DC) for their guidance, suggestions, and encouragement. Kate Dooley would like to thank the National Gallery of Art for financial support.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. Related group of drawings to Ballet Scene by Edgar Degas includes three private collection drawings: Quatre Danseuses Nues, c. 1905–1912, charcoal on paper, 57.15 × 48.26 cm; Deux Danseuses Debout Étude, c. 1905–1912, charcoal on paper, 53.34 × 58.42 cm; Groupe de Trois Danseuses Debout, c. 1905–1912, charcoal and pastel on tracing paper, 58.42 × 54.61 cm. Dancers, Entrance on Stage, c. 1898–1908, pastel on tracing paper, 73.66 × 105.41 cm, Carnegie Museum of Art, Pittsburgh. Brodie and Robison 2001, 38–39; Boggs et al. 1988, 576–579. Additionally, an oil painting in the collection of the National Galleries Scotland, A Group of Dancers, has been identified as part of this related group.

2. Charcoal was not detected with NIR reflectance imaging spectroscopy, but its possible presence cannot be ruled out. Degas is known to reverse his charcoal drawings on tracing paper during the mounting process so that the charcoal may be hidden behind the transparent paper support. This technique still provides Degas with underdrawing material to further develop his painterly pastels, but sorely challenges the ability for NIR imaging to detect essentially veiled charcoal lines.

3. In this study, the interpretation of the NIR images was aided as a result of additional analytical instrumentation. The pastels were also found to contain filler and additional pigments identified with FTIR and SEM-EDS of dispersed samples collected from the surface of the pastel. (Facini et al. 2017)

Additional information

Notes on contributors

Kathryn A. Dooley

Kathryn Dooley is a Research Scientist in the Scientific Research Department at the National Gallery of Art in Washington, DC, and is interested in the spectroscopic identification and mapping of materials and chemical imaging methods. She completed a post-doctoral fellowship at the Gallery, where a focus of her research was the identification and mapping of organic binding media in works of art. She graduated with her Ph.D. in Chemistry from the University of Michigan in 2010. Address: National Gallery of Art, 6th and Constitution Ave NW, Washington, DC 20565, USA. Email: [email protected].

Michelle Facini

Michelle Facini is a paper conservator at the National Gallery of Art in Washington, DC, where she performs treatments, makes exhibition and storage recommendations, conducts technical scholarship and advocates for educational outreach and mentorship. Her most recent publications describe the materials and techniques used by Degas in his late pastel works on tracing paper. She has also presented and published research on fifteenth-century Italian illuminated manuscripts and the preservation of oversized artworks. Michelle is a Fellow of the American Institute of Conservation and a former Chair of the Book and Paper specialty group. She received her Master of Science in Art Conservation from the Winterthur/University of Delaware Program and has worked at the National Archives and Records Administration. She participated in fellowships and internships with the British Museum, the California Palace of the Legion of Honor and The Metropolitan Museum of Art. Address as for Dooley. Email: [email protected].