Improved Spectral Imaging Microscopy for Cultural Heritage through Oblique Illumination
This addresses the problem of spectral analysis for cultural heritage works with complex matrices, offering a flexible tool for conservators and researchers, though it is incremental as it builds on existing oblique illumination techniques.
The researchers developed a microscopic chemical imaging platform using oblique illumination to obtain per-pixel reflectance spectra in the VIS-NIR range for cultural heritage analysis, demonstrating its effectiveness on a replica cross-section and a Picasso painting sample to extract rich microscale molecular information.
This work presents the development of a flexible microscopic chemical imaging platform for cultural heritage that utilizes wavelength-tunable oblique illumination from a point source to obtain per-pixel reflectance spectra in the VIS-NIR range. The microscope light source can be adjusted on two axes allowing for a hemisphere of possible illumination directions. The synthesis of multiple illumination angles allows for the calculation of surface normal vectors, similar to phase gradients, and axial optical sectioning. The extraction of spectral reflectance images with high spatial resolutions from these data is demonstrated through the analysis of a replica cross-section, created from known painting reference materials, as well as a sample extracted from a painting by Pablo Picasso entitled La Miséreuse accroupie (1902). These case studies show the rich microscale molecular information that may be obtained using this microscope and how the instrument overcomes challenges for spectral analysis commonly encountered on works of art with complex matrices composed of both inorganic minerals and organic lakes.