Reflectance Transformation Imaging (RTI) Investigation of Engraved Chalk Plaques from the Stonehenge Region

Abstract

Newly discovered and previously documented Late Neolithic chalk plaques from the Stonehenge locality have been subjected to new, non-invasive techniques which allow access to previously unseen elements of archaeological evidence. The application of these methods – involving Reflectance Transformation Imaging (RTI) and Polynomial Texture Mapping (PTM) – has revealed detail of the surface preparation and allowed methods and sequence of the compositions to be unpicked, clarifying their complexities. The results reveal a range of approaches to the compositions, some of which demonstrate planning, order, and intention while others include less systematic, rapidly executed sketches. Investigations of lines and surfaces have been made, supplemented by preliminary studies of replicated test pieces, to examine potential implements used in their creation and remark on plaque biographies and surface attrition following manufacture. Furthermore, detail revealed by RTI provides indications of the orientations in which some of the plaques should be viewed and – in one instance – suggests a ‘reflected’ element that may not be entirely abstract. Results from improved radiocarbon determinations place the plaques in the early part of the 3rd millennium bc which, together with identification of individual motifs, allows the plaques and the designs to be reconsidered within the corpus of Neolithic art in the British Isles.

Digital Rock Art: beyond 'pretty pictures'

“…Recently, RTI has been pivotal in the recording and analysis of Neolithic decorated artefacts from Britain and Ireland, recovering an unprecedented understating of the sensorial manufacturing processes of the objects, phasing and chronology, leading to renewed considerations of their social and cultural roles (e.g. Jones and Díaz-Guardamino, 2019;Davis et al, 2021). Although RTI's set up poses some limitations when used outdoors, the simplicity and portability of both this and SfM photogrammetry have contributed to the generalized use of 3D modelling in all stages of rock art research.…”