Seeing Through Walls: Discovering Europe's Hidden Mural Paintings

The aim of this research proposal is to visualise wall paintings which have been obscured under layers of plaster and paint using a portable pulsed terahertz imaging system. Unlike other technologies used to study wall paintings, terahertz radiation is able to penetrate millimetres of plaster and still detect the obscured picture, while also providing spectral information which can be used to identify the shade and in some cases the age of the wall painting pigment and the covering plaster. Terahertz radiation is non-ionising and non-destructive and will in no way affect the integrity of the artefact under investigation.

Uncovering obscured paintings will be of huge cultural significance to the communities in which they lie dormant. They provide key information about the host building's evolution and influence on the wider community as well as art heritage.

An output of this work would be a multifunction, user orientated, software package to generate numerous 2D and 3D terahertz images, based on properties of the reflected radiation, the physical properties of the pigments used to paint the image, the physical properties of the covering plaster, and thickness of the constituent layers of the wall painting. There will be facilities to generate enhanced spatial resolution at key boundaries in the image and to correct for non-Gaussian noise introduced by uneven plaster surfaces. Optimum image reconstruction methodologies will be identified combining these features. This software will be aimed at non-specialist terahertz users and it is hoped it will be key to integrating the technology with the art heritage community. Commercial aspects of the software will be exploited.

Work will begin using mock wall paintings and will be developed to culminate in testing on actual artefacts. The Centre for Research and Restoration, The Louvre, Paris will provide access to artefacts including fragments of obscured Botticelli paintings housed at the Louvre and access to other obscured paintings in their place of origin across Europe.

Underpinning this software will be key theoretical descriptions of the terahertz radiation as it is reflected from the wall painting and a unique Systems Identification approach which will be taken to solve the terahertz inverse problem. This work will produce fundamental papers for the terahertz research community, essential for the development of terahertz imaging as a generic imaging modality. This work will be, in some cases almost directly, transferable to other application areas.

Academic beneficiaries are detailed in the academic beneficiaries section of the application form: these were specified as Art Conservators, Art Historians and the wider terahertz research community.

Further to these beneficiaries, non-academic beneficiaries will include:

1) The local communities in which the obscured wall paintings are located. The visualisation of these hidden works of art will impact knowledge and understanding of the times when they were created and when they were concealed and will contribute to an evolutionary history of the building in which they are housed. Public addresses will be given at sites of study in the project, and at the Louvre, and it is hoped that these meetings, along with the dissemination of the work through art heritage journals and conferences (see the dissemination section of the case for support) will attract more owners of obscured paintings to come forward.

2) If the hidden painting under study is housed in a building open to the public, an amazing presentation could be created for their public display: reconstructing the obscured image, illustrating in 3D the plaster covering the image etc.

3) Any commercial enterprise which sells portable terahertz devices may benefit from the software produced and wish to licence it alongside their current systems for the benefit of their customers. Our project partners Institute Lumière Extreme, ENSTA, Ecole Polytechnique, Paleisean, France, have established research links with the American firm Picomentrix, Advanced Photonics Inc. The idea of licensing the software will be explored and funds have been requested to achieve this.

The time scale for all of the impact discussed will be initiated within the 36 month time frame of this project.

The proposed fellow, Dr. G.C. Walker, is ideally placed, in terms of her academic career and research output to date, to pursue and fulfil the aims and objectives of this proposal. This is indicated by the number of her publications which are directly applicable to this work. She is a skilled and practised communicator of scientific ideas to people with a range of academic levels. The collaboration arrangements (which will be discussed more in the impact plan) are ideal to conduct and exploit the research. Our project partners already have established research links with the Louvre and Picometrix, the team at Reading has in depth knowledge of fundamental terahertz science and Dr. Walker herself has a background in image analysis.