Improved Spectral Imaging Microscopy for Cultural Heritage through Oblique Illumination

TL;DR

This paper introduces a flexible spectral imaging microscope with oblique illumination for cultural heritage analysis, enabling detailed molecular imaging of artworks with complex matrices.

Contribution

It develops a novel, adjustable oblique illumination system for spectral microscopy that enhances surface normal and axial imaging capabilities in cultural heritage studies.

Findings

Successfully imaged a Picasso painting sample revealing molecular details.

Demonstrated high spatial resolution spectral reflectance imaging.

Overcame challenges of spectral analysis on complex art materials.

Abstract

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 Mis\'ereuse 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.