This presentation is part of the 2017 3D Digital Documentation Summit.
Photogrammetric gigapixel imaging of monumental wall paintings using visible, infrared and ultraviolet radiation.
The challenges of documenting wall paintings are severe; limited access, large scale, immovable heterogeneous condition and technology, complex geometry. However, digital imaging can now overcome many of these challenges, allowing us to digitally interrogate the surface of wall paintings in ways previously limited to small sections of the whole painting or museum pieces such as panel and canvas paintings. The increased availability of high-quality imaging hardware and software puts in the hands of the conservator digital tools to accurately document and investigate wall paintings, aiding the conservator in the understanding of original technology, non-original materials, physical history and condition.
This paper will discuss the innovative use of high resolution photogrammetric imaging with visible, infrared (IR) and ultraviolet (UV) radiation. A structure-from motion software package (Agisoft’s Photoscan) was used to process large sets of images (>200 individual images) to create orthomosaics of the paintings under reflected visible and IR (X-Nite, 830nm cutoff at 50%) radiation as well as using UV-induced visible fluorescence (365nm). The resultant orthomosaics can also be processed into IR-false colour images to aid in pigment identification, areas of repainting etc.
This technique has been employed in the preliminary stages of two conservation projects, Daniel Maclise’s monumental wall paintings in the Palace of Westminster and Sir James Thornton’s masterpiece in the Old Royal Naval College in London, UK, and form the case studies for this paper. Photogrammetic imaging has allowed the paintings to be visualized in new ways overcoming the constraints of imaging wall paintings in their architectural context. The combination of the three types of imaging, visible, IR and UV builds up a comprehensive record of how the paintings respond to radiation across the spectrum. This means we can map areas of repainting, varnishes, areas of deterioration in unprecedented detail and visualize this without perspectival distortion; usually a challenge with the documentation of wall paintings. Furthermore, it helps inform the conservation decision making process as well as being an archival record of the paintings prior to conservation.
The methodology of these techniques was specially designed to overcome the challenges of accurately, effectively and efficiently documenting, insitu, large scale wall paintings in high resolution. The use of a flash-based system for the UV fluorescence and IR reflected imaging facilitated imaging from scaffolding with short exposure times (<60th second), during daylight hours and whilst visitors and staff were also using the space. This flexibility in how the images are captured means the process can be incorporated into the conservation workflow where scaffolding is usually required for access.
These techniques can be built into conservation workflows at minimal cost whilst providing high quality qualitative and quantitative data and archival records and are an exciting development in how wall paintings are imaged.
Samuel Whittaker undertook an MA in the Conservation of Wall Painting at The Courtauld Institute of Art. His research dissertation focused on non-invasive investigations of fluorescent properties of natural organic colorants. He then took up a graduate internship at the Getty Conservation Institute in Los Angeles. During this internship he researched the application of 3D-imaging techniques to map deterioration phenomena and quantify rates of change through image analysis. He has been a conservator on projects in the UK and on Courtauld projects in India, Bhutan and Cyprus and has supervised MA conservation students at Bundi in India, Tamzhing in Bhutan and Vardzia in Georgia.