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The University of Kent, Canterbury, Kent, CT2 7NZ, T +44 (0)1227 764000
OCT for Art Conservation
Project Outline
The conservation and historical study of art works require a degree of scientific examination of a cross-sectional slice of the piece. Current practice is to remove a small sample of the painting and examine this under a microscope. Clearly, non-invasive methods are to be much preferred, but most current techniques, such as infrared photography and x-radiography, provide little or no selection in depth; they produce essentially 2D representations. Optical Coherence Tomography (OCT), a technology primarily developed for imaging of the eye and skin, is an imaging system which does provide this selection in depth, thus allowing a cross-sectional or even a 3D image to be acquired without compromising the painting. In a collaboration with the British Museum, the National Gallery and Nottingham Trent University, we are investigating the potential for OCT to assist with the conservation of paintings and other historical artifacts. Financial support is provided by the Leverhulme Trust.
An OCT system is essentially a Michelson interferometer; light from a coherent source (a laser or super-luminescent diode) is split into an object and a reference beam. The object beam is reflected off the object under study whilst the reference beam is reflected off a mirror. The two beams are then recombined, giving rise to interference effects when the lengths of the two arms are equal to within the coherence length of the source. Hence by subtracting the d.c. term of the output signal, and considering only the interference pattern, it is possible to select light from a specific depth layer.
At Kent, we have designed and built a portable time-domain OCT system (PILOT) to be used in-situ at the National Gallery and British Museum. Use of the time-domain modality allows use to generate fast en-face scans which is essential for the viewing of under-drawings. We are also investigating several other avenues which have applications in art imaging, including speckle reduction and removal of mirror terms in Fourier-domain imaging.
Figure 1: An OCT 'B' scan (cross-section) of a sample of malachite paint at 1300nm.
Figure 2: A graphite under-drawing hidden under a layer of Cerulean Blue is revealed using en-face OCT operating at 1300nm.
Figure 3: A 3D scan of a sample of Malachite paint using PILOT. The image was assembled from a stack of 100 en-face scans.
Staff Involved
Michael Hughes (University of Kent)
Adrian Podoleanu (University of Kent)
Boco Peric (Nottingham Trent University)
Haida Liang (Nottingham Trent University)
Marika Spring (National Gallery)
David Saunders (British Museum)
Publications
1. Haida Liang, Marta Cid, R. Cucu, G. Dobre, A. Podoleanu, Justin Pedro, and David Saunders, En-face optical coherence tomography - a novel application of non-invasive imaging to art conservation,Optics Express, Vol. 13, Issue 16, pp. 6133-6144
2. Haida Liang, Borislava Peric, Michael Hughes, Adrian Podoleanu, Marika Spring, and David Saunders, Optical coherence tomography for art conservation and archaeology, Proc. SPIE Vol. 6618, 661805 (Jul. 16, 2007)