Non-destructive method for the identification of ceramic production by portable X-rays Fluorescence (pXRF) : A case study of amphorae manufacture in central Italy

Portable X-rays Fluorescence (pXRF) represents one of the most effective tools for in situ, non-destructive elemental analysis, which has a valuable application in the study of ceramic production. However, whilst the qualitative assessment of the composition of artefacts is reliable, the quantitative analysis can be biased by some limitations, due to instrumental features or materials properties. The analysis of ceramic materials is particularly challenging due to the lack of representative calibrations and standards, as well as the low density and poor homogeneity of samples. In this contribution, a method is proposed to fingerprint a ceramic production through pXRF analysis. At the site of Montelabate (Perugia) in central Italy four kilns were excavated revealing a production of amphorae. This site was therefore selected as a suitable case study for fingerprinting a ceramic production. After qualitative analysis, representative calibration standards were created based on different commercial clays and feldspars. These can help overcoming the well-known matrix effect, both physical and chemical, and may offer a representative and reproducible standard to be used in different laboratories. Alongside the precise assessment of composition, the possibility to fingerprint a production was also assessed using a different method, based on the intensity ratio between selected elements. The relevant elements were chosen based on their correlation and non-correlation. Correlated elements were attributed to the raw clay used for ceramic production and non-correlated elements were attributed to the specific fabric recipe. Accordingly, some benchmarks to identify the clays and fabric used in the site of Montelabate were identified. Amphorae found at other ancient commercial sites in the area of Rome were therefore also compared with these benchmarks in order to assess their provenience.