Research Project - The Next Generation Optical Coherence Tomography (OCT) for Art Conservation

The Next Generation Optical Coherence Tomography (OCT) for Art Conservation - in situ non-invasive imaging of the subsurface microstructure of objects

Principal Investigator:

Haida Liang

Co-Investigators:

Marika Spring, The National Gallery (London)
Andrew Clarkson, Optoelectronics Research Centre, University of Southampton

Project Partners:

Research Fellow:

Sammy Cheung (Nottingham Trent University)
Masaki Tokurakawa (University of Southampton)

PhD Student:

Jae Daniel (University of Southampton)

Sponsors: AHRC and EPSRC, under the Science and Heritage Programme

Value: £823,673 FEC

Duration: 5 July 2010 – 4 July 2013

Details:

Optical Coherence Tomography (OCT) is an imaging method based on a fast scanning Michelson interferometer. Originally designed for biomedical applications such as in vivo examination of the eye, it is capable of non-invasive 3D imaging of subsurface microstructure. In previous projects funded by the Leverhulme Trust, EPSRC and the National Gallery, we were able to demonstrate the potential application of OCT to art conservation, art history and archaeology including:

non-invasive imaging of paint and varnish layers
dynamic monitoring of varnish removal using solvents
high resolution depth-resolved imaging of underdrawings (preparatory sketches)
dynamic monitoring of the drying and surface formation of different varnishes
non-invasive imaging of deterioration crusts on glass
non-invasive imaging of surface texture of jade to determine the tool marks
non-invasive imaging of glaze on ceramics and faience.

While current OCTs have shown potential in this field, they are optimised for biomedical applications. Some major limitations are: (i) lower depth resolution compared to conventional microscopic examination of paint cross-sections; (ii) limited probing depth through highly scattering paint.

This new project aims to significantly improve the capabilities of OCT through increasing the depth resolution and the probing depth in order to:

reduce the need for sampling and enable the subsurface microstructure to be imaged on intact objects where sampling is not possible.
encourage more frequent and thorough examination of the whole object for early warning of deterioration.
improve the visibility and resolution of underdrawing on paintings for art historical research.
firmly establish OCT as a tool for non-invasive imaging in the heritage field.
to inform conservation strategy and create long term savings in the cost of conservation through monitoring degree of deterioration.
explore new problems in conservation and art history that the next generation OCT can help to solve.

Increasing the depth resolution involves broad band sources and increasing the probing depth needs sources at longer wavelength than the conventional wavelength range used in biomedical imaging. Specifically two OCT systems will be built so that used in conjunction, they would aim to match the information from conventional microscopic examination of sample cross-sections:

An 800nm OCT optimised for imaging at high depth resolution: targeted towards applications where highest resolution is required but the material is relatively transparent, such as imaging of multiple thin varnish layers on painting surfaces or glazes on the surface of ceramics and enamels.
A 2000nm OCT optimised for deeper penetration suitable for imaging cultural heritage objects consisting of more highly scattering materials. This would allow improved imaging of highly scattering paint layers and underdrawing beneath them (at higher lateral resolution than conventional infrared imaging), pigmented objects such as coloured enamels and glass with opacifiers.

Latest News:

Ultra-high resolution OCT at 800nm developed and verified to have reach the theoretical depth resolution of ~2.1 microns in air (or 1.4 microns in paint and varnish).
A first version of swept source at wavelength of ~2 microns has been developed.

Conference Presentations

Invited talk on “Contributions of astronomy to the study of art conservation and archaeology” at the workshop From Antikythera to the Square Kilometre Array: Lessons from the Ancients, 11-16 June 2012.
Invited talk on “Non-invasive investigations of a wall painting using optical coherence tomography and hyperspectral imaging”, O3A: Optics for Arts, Architecture and Archaeology, World Photonics Congress, 26th May 2011 Munich, Germany
Invited talk on “Optical Coherence Tomography for the Non-invasive Subsurface Imaging of Wall Paintings and Stones”, at Going beneath the surface - ICON Stone and wall paintings conference, Institute of CONservation (ICON), London, 5th November 2010
Invited talk on “Next Generation Optical Coherence Tomography for Art Conservation” at the Research in the Historic Environment Seminar, English Heritage, London, May 2010
Presentation by Rebecca Lange on “Application of Optical Coherence Tomography to the Subsurface Imaging of Wall Paintings” at the international workshop “Application of imaging science to the interdisciplinary study of wall paintings along the silk road”, 1 - 3 December 2010, Xi’an China
Presentation by Elizabeth Bemand on “Optical Coherence Tomography for non-invasive in-situ monitoring of the bioreceptivity of sandstone monuments” at the International Conference on the Research and Conservation of the Kucha Caves, August 2011 Kizil, China
Presentation by Rebecca Lange on “Non-invasive imaging of archaeological tool marks with OCT”, Photonex Optical Metrology Meeting, October 2011, Coventry
Presentation by Jae Daniel on “Power-scalable wavelength-agile fibre laser source at two microns” at Europhoton 2012

Upcoming conference presentations:

Sammy Cheung at OCT4NDT 13-14 February 2013, Linz, Austria

Recent Publications:

Liang H., Sax M., Saunders D., Tite M., Optical Coherence Tomography for the non-invasive investigation of the microstructure of ancient Egyptian faience, Journal of Archaeological Science, 39, pp. 3683-3690 (2012)
Lawman S., Liang H., High precision dynamic multi-interface profilometry with optical coherence tomography, Applied Optics, 50(32) 6039–6048 (2011)
Lange R., Liang H., Howard H., Spooner J., Optical coherence tomography and spectral imaging of a wall painting, SPIE Newsroom, August 2011 (more information can be found here)
Liang H., Lange R., Howard H., Spooner J., Non-invasive Investigations of a Wall Painting using Optical Coherence Tomography and Hyperspectral Imaging, Proc. SPIE (2011) Vol. 8084, 80840F-1
Liang, H., Advanced Optical Imaging Methods for Investigating Manuscripts, in Ch.8 of The Technological Study of Books and Manuscripts as Artefacts - Research questions and analytical solutions, eds. Sarah Neate, David Howell, Richard Ovenden, A.M.Pollard, Archaeopress, Oxford, 2011

Links:

An article about the Application of a New Non-invasive Technique (Optical Coherence Tomography) to Paintings Conservation Project in the January 2011 issue of the Leverhulme Trust Newsletter
Full list of Publications can be found on the OCT for art website