Energy dispersive X-ray fluorescence spectrometry characterization of wall mortars with principal component analysis: Phasing and ex situ versus in situ sampling

Abstract

Mortared stone walls at the Coriglia, Castel Viscardo archaeological excavation site near Orvieto, Italy were analyzed via portable X-ray fluorescence (XRF) spectrometry to better understand their construction sequence and phasing. Data were collected ex situ for intact, ground, and fused bead samples and in situ at the site and evaluated through principal component analysis. Elements identified in the mortars included calcium, manganese, iron, nickel, zinc, rubidium, and strontium. Conclusions regarding wall associations agreed among the three ex situ sample forms, demonstrating that sample form does not matter when applying portable XRF spectrometry for mortar analysis. Conclusions drawn from the ex situ and in situ data and from visual observations by the site archaeologists also agreed and provides additional support for the use of XRF spectrometry for phasing of mortared walls. Lastly, this study demonstrates that in situ data collection for archaeological mortars is valid while also ensuring the preservation of cultural heritage objects.