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Thursday, May 29 • 4:00pm - 4:30pm
(Research and Technical Studies Session) Unwrapping Layers in Historic Artworks: Virtual Cross-Sections with Pump-Probe Microscopy

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The layering structure of a painting contains a wealth of information about the artist's choice of materials and working methods; information which leads to greater understanding of past cultures and can provide conservators with a better means of how to preserve that culture. The study of such three-dimensional (3d) structure has generally required the physical removal of a cross-section sample, which is then characterized by a plethora of analytical techniques. While current noninvasive techniques, such as x-radiography, infrared reflectography, ultraviolet visible fluorescence photography, Raman (1-3), reflectance imaging spectroscopy (4) and x-ray fluorescence intensity mapping, provide important information about a painting, these techniques cannot provide quantitative depth information. Conservation scientists are exploring 3d imaging techniques that would avoid invasive sampling, such as confocal x-ray fluorescence (XRF), absorption near edge structure imaging (XANES)(5), optical coherence tomography (OCT)(6) and terahertz imaging (7), but these are research tools and not yet in common use. Unfortunately, no single technique can provide the resolution, penetration, chemical specificity, and ease-of-use for broad use in the conservation field.
Optical microscopy is both non-invasive and yields high-resolution, but conventional linear optical contrast is limited in use for studying artist pigments due to absorption in the pigments and scattering from other materials in the paintings. In similarly scattering samples, such as biological tissues, optical nonlinear imaging has been utilized to obtain high resolution 3d images. Established nonlinear imaging, such as two-photon fluorescence and second- or third-harmonic generation imaging, has had some success in studying binders, varnishes (8), or wood in musical instruments (9), but applications in cultural heritage are sparse because most inorganic pigments do not fluoresce or generate harmonic light.

Recently we have developed an optical nonlinear imaging technique, pump-probe microscopy, to image the biological pigments hemoglobin (10), eumelanin, and pheomelanin (11) which are present in skin cancer (12) and ocular melanoma (13). Extension of pump-probe microscopy from biological pigments to artist’s pigments has yielded promising preliminary results (14), however, achieving pump-probe contrast in fine arts objects is more challenging than skin because the artist’s palette has a much greater variety of pigments than those present in skin. Here we show that by tuning to appropriate choices of wavelength and pulse parameters we can obtain in-situ 3d imaging of paintings with molecular specificity. We generated virtual cross-sections in mock-up paintings with clear distinction between mixed and layered stratigraphy with pigment specificity. We also imaged an intact 14th century painting, The Crucifixion by Puccio Capanna, leaving no visible signs of damage. Although we focus mainly on historic paintings, our approach can be applied to a wider range of cultural heritage objects, such as pottery or statuary, and provide information relevant to current areas of interest in conservation science.


Tana Villafana

Graduate Student, Duke University
I am a laser and imaging scientist excited about cultural heritage research. My focus is on creating non-invasive virtual cross-sections using a nonlinear microscopy technique.

avatar for John Delaney

John Delaney

Senior Imaging Scientist, National Gallery of Art
John K. Delaney, Ph.D. is the Senior Imaging Scientist at the National Gallery of Art, where his research focuses on the development and application of remote sensing imaging methods for the study of works of art.

Martin C. Fischer

Assistant Research Professor, Duke University
Dr. Fischer’s research focuses on exploring novel nonlinear optical contrast mechanisms for molecular imaging. Nonlinear optical microscopes can provide non-invasive, high-resolution, 3-dimensional images even in highly scattering environments such as biological tissue. Established... Read More →
avatar for Michael Palmer

Michael Palmer

Conservation Scientist, National Gallery of Art
Michael Palmer received his graduate training in botany from the University of Maryland in 1979. From 1980-1985 he held the position of wood researcher at Winterthur Museum and also taught in the conservation training program. Mr. Palmer joined the National Gallery of Art in 1985... Read More →

Warren S. Warren

ames B. Duke Professor of Chemistry, Professor of Radiology, Biomedical Engineering, and Physics, Duke University
avatar for William P. Brown

William P. Brown

Chief Conservator, North Carolina Museum of Art
William Brown is Chief Conservator of the Art Conservation Center (ACC) of the North Carolina Museum of Art (NCMA) where he is responsible the long-term preservation of the collection and the development of preventive collections care strategies. He is a leader in the field of art... Read More →

Thursday May 29, 2014 4:00pm - 4:30pm PDT
Seacliff C-D