Application example: Validating on-site materials analysis

Modern archaeological sciences are well aware of the impact that excavations and the removal of artefacts from their find context have. Today, treating humanities’ cultural heritage respectfully has highest priority and artefacts should be left at their place of origin. However, not all sensitive instrumentation is mobile and can be brought to an excavation site. Mobile instruments may be far less sensitive than the specialized immobile equipment. An example from Amarna (Egypt) shows, how reliable conclusions on the provenance of artefacts can be drawn nevertheless: by validating less sensitive mobile methods with highly sensitive non-mobile methods of ion beam analytics.

Excavations in the late bronze age settlement of Amarna, a seat of the ancient Egyptian pharaohs, started in the early 19th century. Numerous glass artefacts from Amarna have been transferred to European museum, among them the Egyptian Museum of Berlin. Recently, the export of artefacts is much more strictly controlled and sometimes prohibited. Thus, newly found artefacts can often only be investigated with mobile methods such as pXRF (portable X-ray fluorescence) for materials analysis. It must therefore be clarified, whether pXRF can provide sufficiently meaningful data for, e.g., provenance studies. To this ends, a number of glass artefacts originating from Amarna and held by the Egyptian Museum of Berlin were analysed by ion beam methods. The results were compared to those of pXRF measurements taken on artefacts on site in Amarna. By means of the methods PIXE and PIGE (proton-induced X-ray and gamma emission) ion beam analysis can provide precise information about the material composition including trace elements. This enables tracing back individual artefacts to specific metal ore deposits and production periods based on their characteristic content of trace elements. Ion beam analysis of the objects in the Egyptian Museum showed that their contents of the elements cobalt, manganese, zinc, and nickel are decisive for their categorization and connection to ore deposit sites. On-site measurements during a recent excavation campaign in Amarna demonstrated that pXRF can indeed detect these elements with the required precision. Thus, pXRF is verified as a reliable mobile method for provenance determination in this context. Additionally, the ion beam analytics method RBS (Rutherford Backscattering) can reveal differences between the compositions of the object surface and its bulk, indicative of changes in the material due to weathering which must be considered in the evaluation of pXRF data.

While the practice of removing artefacts from their archaeological find context is regarded very critically today, objects that have already been transferred to museums in the past can provide valuable information, as they can be available for analysis by non-mobile methods. Comparing the results of highly sensitive methods such as ion beam analytics with those of mobile methods such as pXRF can be used to validate the latter for gathering data on-site. Thus more data sources can be exploited without disturbing find contexts, removing artefacts from their region of origin, or jeopardizing their conservation status by transport.

• A.K. Hodgkinson et al., A comparative compositional study of Egyptian glass from Amarna with regard to cobalt sources and other colourants.
  Journal of Archaeological Science: Reports 54 (2024) 104412
  https://doi.org/10.1016/j.jasrep.2024.104412