Reflection imaging spectroscopy is a useful technique to remotely identify and map minerals and vegetation. Here we report on the mapping and identification of artists' materials in paintings using this method. Visible and infrared image cubes of Picasso's Harlequin Musician are collected using two hyperspectral cameras and combined into a single cube having 260 bands (441 to 1680 nm) and processed using convex geometry algorithms. The resulting 18 spectral end members are identified by comparison with library spectra, fitting by nonlinear mixing, and using results from luminescence imaging spectroscopy. The results are compared with those from X-ray fluorescence spectrometry, polarized light microscopy, and scanning electron microscopy-energy dispersive spectrometry (SEM/EDS). This work shows the potential of reflection imaging spectroscopy, in particular if the shortwave infrared region is included along with information from luminescence imaging spectroscopy.

Paper Conservation Department, National Gallery of Art, Washington, DC, USA A paradigm using multispectral visible and near-infrared imaging spectroscopy is presented to semiautomatically create unbiased spectral maps that guide the site selection for in situ analytical methods (e.g. fiber optic reflectance spectroscopy and X-ray fluorescence) in order to identify and map pigments in illuminated manuscripts. This approach uses low spectral resolution imaging spectroscopy to create maps of areas having the same spectral characteristics. This paradigm is demonstrated by analysis of the illuminated manuscript leaf Christ in Majesty with Twelve Apostles (workshop of Pacino di Buonaguida, c. 1320). Using this approach the primary pigments are mapped and identified as azurite, lead-tin yellow, red lead, a red lake (likely insect-derived), a copper-containing green, brown iron oxide, and lead white. Moreover, small amounts of natural ultramarine were found to be used to enhance the blue fields around Christ, and a red lake was used to highlight different colors. These results suggest that the proposed paradigm offers an improved approach to the comprehensive study of illuminated manuscripts by comparison with site-specific analytical methods alone. The choice of broad spectral bands proves successful, given the limited palette in illuminated manuscripts, and permits operation at the low light intensity required for examination of manuscripts.

No abstract