Optimum spectral window for imaging of art with optical coherence tomography

Abstract

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 noninvasively. However, its depth of penetration in painted objects is limited due to the strong scattering properties of artists' paints. VIS-NIR (400 nm -2400 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 optical coherence tomography (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 microns are highly desirable for OCT applications in art and potentially material science in general.

Three-band, 19-μm axial resolution full-field optical coherence microscopy over a 530–1700 nm wavelength range using a single camera

“…5 that one of the pigment absorbs light between 600 and 1000 nm (band 1 and 2) and appears red in the RGB image, whereas the other pigment absorbs the visible (band 1) and infrared light beyond ∼1.3 μm (part of band 3) and then appears greenish in the RGB representation. This is consistent with the spectroscopic properties of the Prussian blue and Cerulean blue oil paintings [13]. An example of how three-band FF-OCM can be used for biological sample characterization is shown in Fig.…”

A high sensitivity, low noise and high spatial resolution multi-band infrared reflectography camera for the study of paintings and works on paper

“…The camera system had to operate over the complete spectral range identified as providing the most usable information: 1000 to ~2500 nm. The selected spectral range of 1000-2500 nm is based on the prior studies of the wavelength dependence of the transmission of the paint layer [1,6] and also a study that included the effect of the underdrawing material and the paint grounds [4]. This latter study examined only five spectral regions from 900 to 2500 nm.…”

“…Several studies have summarized the results of experiments aimed at finding the 'optimal' spectral transmission window for pigments and paints used by artists [1,[4][5][6]. In general, such studies have found increasing transmission of light starting around ~700 nm and peaking at about ~2000 nm.…”

Determination of thickness of thin turbid painted over-layers using micro-scale spatially offset Raman spectroscopy

“…The output of micro-SORS is compared with the results of the optical coherence tomography (OCT) technique that has emerged in substitution of invasive methods capable of recovering the cross-sectional structural information. OCT is a well established optical interferometric technique, particularly suited for probing semi-transparent materials in the medical field, mainly in ophthalmology, and recently also in cultural heritage to study stratified systems of paintings [5][6][7][8][9]. both mixed in acrylic media, here referred to as 'R' (red) and 'B' (blue).…”