In-fiber optical coherence tomograph for examination of paintings

Scientific examinations of paintings are routinely carried out in major galleries and museums to assist in conservation treatment and as part of technical or art historical examinations. Care is taken to examine the paintings non-destructively as far as possible. However, in order to study the paint and varnish layers, it is still currently necessary to take tiny samples of a painting to examine the cross section of a small area of the painting under a microscope. In an attempt to solve this problem we evaluate the potential of optical coherence tomography (OCT) in providing high resolution information about paint layers. Two OCT systems have been assembled, operating at 850 nm and 1300 nm, each using two single mode in-fiber couplers. Both systems can produce A (reflectivity profile in depth), T (lateral reflectivity profile), B (cross section image) and C-scans (constant depth image). Using superluminiscent diodes, a depth resolution better than 9 microns is achieved. We present results of applying OCT to sample panels and paintings. We show that infrared OCT is capable of non-destructive examination of paintings in 3D, which shows not only the structure of the varnish layer but also the paint layers. The OCT images present better microscopic tomography of the surface of the varnish and paint layers than any system currently employed in the examination of paintings. OCT could also be used for accurate measurement of the thickness of the varnish layer on a painting.