Revealing the Past Without Damaging it: Optical Coherence Tomography (OCT) for Heritage Science

Allowing in-tact objects to be examined

Looking deeper into the surface of a painted work of art can give us fascinating clues into its history. However, analysing the substructure of paintings without damaging them is a challenge – and often banned by conservation ethics. Using fast scanning techniques stretching back to the late 19th Century, Professor Haida Liang has pioneered a technique that allows us to see into the surface without needing to take samples.

Optical Coherence Tomography (OCT) is an imaging method based on a fast scanning Michelson interferometer, capable of non-invasive 3D imaging of subsurface microstructure, Professor Liang saw the potential of OCT technology to examine subsurface microstructures of art works without damaging them.

In the heritage context, OCT permits the (non-destructive) examination of artefacts. It allows us to peer into layers of paint and varnish, jade, glass, enamel, amongst others. It enables the high-resolution, high-contrast, depth-resolved imaging of underdrawings. It can be used to dynamically monitor varnish as it dries, and to measure the rate of water transfer in sandstone monuments.

Professor Haida Liang is Head of the Imaging & Sensing for Archaeology, Art History & Conservation (ISAAC) research group.

Teaching duties include: Module Leader for Year One Concepts of: Astronomy and Cosmology, Year Three Cosmology: Theory and Observation; teaching contributions to Year Two Stars & Galaxies, MSc Medical Imaging and MSc Materials and Security Imaging. Areas of research include the development of advanced optical imaging and spectroscopic instruments for non-invasive and non-destructive examination, applications of physics (particularly imaging and optics) to art conservation and archaeology, as well as astrophysics.

Professor Haida Liang pioneered the application of OCT to cultural heritage in 2004. Her Imaging and Sensing for Archaeology, Art history and Conservation (ISAAC) lab at NTU continues to demonstrate its potential. Recent research has resulted in the development of two next-generation OCT devices tailored to heritage applications.

Informing conservation strategy

The team has developed two next-generation OCTs for ultra-high resolution imaging of transparent surface layers and imaging at long wavelength for increased penetration. Demonstrating the potential of OCT to heritage institutions has helped lead to funding from international bodies such as the Leverhulme Trust, National Gallery (UK), Brooklyn Museum (USA), National Museum of Ireland, Dunhuang Academy (China), and C2RMF (France).

NTU’s research has firmly established OCT as a tool for rapid non-invasive imaging in the heritage field. Artefacts can be examined more frequently and more thoroughly, and signs of deterioration can be spotted earlier. This informs conservation strategy, guides the cleaning of paintings, and leads to long-term savings. OCT also gives us improved visibility of the underdrawings hidden inside paintings – an invaluable tool for historical research in art.