Optimum spectral window for imaging of art with optical coherence tomography
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Optical coherence tomography (OCT) has been shown to have potential for important applications in the field of art conservation and archaeology due to its ability to image subsurface microstructures non-invasively. However, its depth of penetration in painted objects is limited due to the strong scattering properties of artists’ paints. VIS–NIR (400–2,400 nm) reflectance spectra of a wide variety of paints made with historic artists’ pigments have been measured. The best spectral window with which to use OCT for the imaging of subsurface structure of paintings was found to be around 2.2 μm. The same spectral window would also be most suitable for direct infrared imaging of preparatory sketches under the paint layers. The reflectance spectra from a large sample of chemically verified pigments provide information on the spectral transparency of historic artists’ pigments/paints as well as a reference set of spectra for pigment identification. The results of the paper suggest that broadband sources at ~2 μm are highly desirable for OCT applications in art and potentially material science in general.
KeywordsOptical Coherence Tomography Spectral Reflectance Optical Coherence Tomography Image Paint Layer Paint Sample
Funding by the Royal Society, the Leverhulme Trust, EPSRC CASE award, AHRC/EPSRC Science and Heritage Programme and Nottingham Trent University is gratefully acknowledged. We would like to acknowledge Sophie Martin-Simpson of Nottingham Trent University and Rachel Morrison of the National Gallery for preparing some of the historic artists’ paint samples, Gareth Cave of Nottingham Trent University for the XRD confirmation of realgar and orpiment, Rachel Billinge of the National Gallery for allowing us to use the detail of the infrared reflectogram made with the SIRIS and OSIRIS cameras in Fig. 10b and Fig. 11b, and Sammy Cheung of Nottingham Trent University for taking the images in Fig. 2a, b.
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