Reflectance Transformation Imaging for the Study of Ancient Documentary Artefacts (RTISAD)


Exploring Ancient Writings at the Ashmolean Museum with Advanced Digital Technologies

Kathryn E. Piquette, Jacob L. Dahl, Jack D.M. Green

Autumn 2010 saw the arrival of a powerful digital imaging system at the Ashmolean Museum. As part of “Reflectance Transformation Imaging (RTI) System for Ancient Documentary Artefacts”, a collaborative pilot project between the University of Oxford (Faculty of Oriental Studies and Faculty of Classics) and the University of Southampton (Electronics and Computing Science and Department of Archaeology), funded by the Arts and Humanities Research Council, the RTI system is being tested on a range of inscribed artefacts from amongst the rich and diverse collections of the Department of Antiquities at the Ashmolean Museum. The imaging system developed by the project will allow researchers to study documentary and other artefacts remotely (online) in great detail and without being restricted by the fixed lighting angles of traditional photography and flatbed scanning* where details can be obscured by shadows. In developing the RTI system, the project aims to ensure that high-quality digital images of inscribed artifacts, viewable from multiple light sources, can be consulted by scholars and the general public around the world.

* High-resolution images of the Ashmolean’s collection of inscribed cuneiform clay tablets and prisms have been captured using flatbed scanners as part of the Cuneiform Digital Library Initiative (CDLI).

Fig.1: The black plastic dome used for the RTI system
(camera mounted at top).

The system’s hardware consists of a segmented black plastic dome measuring one metre in diameter (Figure 1). 76 LEDs (Light Emitting Diodes) are mounted onto its interior surface. A Nixon DX3 camera is suspended from an aluminium frame over the opening in the apex of the dome, capturing at a resolution of 24.5 megapixels – the highest resolution of any RTI lighting dome currently in use. Artefacts are carefully placed on a padded tray affixed to a small scissor lift, moved into place under the dome directly below camera’s lens, and raised up to the level of the focal plane. Black fabric skirting ensures that no external light can penetrate the dome. Photography involves a sequence of 76 shots for a single object (or side of an object), each taken with a different LED turned on while the rest are turned off. This process is controlled from a computer using special RTI capture software (which continues to undergo improvements for speed) currently taking about two and a half minutes. Image fitting software amalgamates the 76 image files into a single file called a ‘Polynomial Texture Map’ or PTM. The PTMs can then be studied using a special viewing interface which allows the user to recreate the different lighting conditions crucial for the location, enhancement and interpretation of surface modifications on artefacts, such as inscriptions or other marks.

click for zoomable version
Fig.2: Clay tablet bearing an administrative
text in Sumerian cuneiform, dated to the
Ur III period (2100-2000 BC). From Tell Jokha
(ancient Umma), Iraq (AN1911.191). RTI helps
flesh out the impressions of a cylinder seal
rolled over the inscription.
Click for zoomable version of this image

The testing of the RTI system at the Ashmolean is already proving to be a major step forward in documenting writing and/or images rendered on undulating, convex or concave material surfaces. Jacob L. Dahl (Faculty of Oriental Studies) and Kathryn E. Piquette (Faculty of Classics), working closely with Department of Antiquities curators Susan Walker, Jack Green and Liam McNamara, as well as Conservation Department staff, have been selecting objects with complex surface features from the collections. Stylus impressed clay tablets from Ancient Iraq bearing cuneiform (wedge-shaped) script, the world’s most ancient writing system (Figure 2), as well as inscribed ivory, bone and wooden funerary labels representing the earliest writing system in Egypt’s Nile Valley (Figure 3) are among the treasures from the Ashmolean being imaged for this pilot project. Some artefacts were selected because their inscriptions have proved difficult to decipher – even through close first-hand inspection under good light – while others were chosen for the clues they hold to understanding more about the particular tools and techniques that ancient scribes used to create their documents. The extent of the detail and precision obtained by the RTI system is also apparent in [Figure 4] where, despite some corrosion, the delicate yet densely inscribed signs on a Mandaic lead roll are clearly visible using the ‘specular enhancement’ setting in the RTI viewing software. As the technology develops, the results improve and the analysis continues, new and exciting discoveries will undoubtedly be made.

click for zoomable version

Fig.3: Fragment of an elephant ivory label bearing some of the earliest Egyptian writing, dated to the 1st Dynasty (c. 2700 BC), from Abydos, Egypt (E1122). RTI shows possible erasure marks on the upper left below hieroglyphic signs of a ‘cylinder seal on a lanyard’ and a ‘bee’.
Click for zoomable version of this image

click for zoomable version

Fig. 4: Before and after: close-up of a lead roll amulet (unrolled in modern times, width c.5cm) inscribed in Mandaic script, dated to c. 5th century AD, Iraq (no provenance, AN1931.474). Corrosion obscures part of the inscription from the naked eye. The lower image shows specular enhancement of the same image. This setting allows the purely reflective characteristics of an object’s surface to be viewed independently of, or in combination with, the colour properties. It discloses a high degree of information about small changes in surface features.
Click for zoomable version of this image

Considerable momentum is building behind RTI technologies given the tremendous opportunities for detailed study of ancient texts and other artefacts through high-resolution digital images. The Ashmolean Museum with its world class collections is providing vital support for the development of this suite of digital technologies that will not only increase collections accessibility for students and researchers, but will also provide enhanced access for the general public. Indeed, all partners in the project share a commitment to opening digital access to cultural heritage; the results will be made publicly available through the development and use of open source software, allowing a wider range of users to take advantage of this illuminating new technology.

February 2011