New perspectives on the use of FTIR for studying the relative proportions of anthropogenic and geogenic calcium carbonate: the application of peak height and area ratios

Abstract

Fourier-transform infrared spectroscopy (FTIR), a micro-invasive, minimally destructive technique, which allows to analyse archaeological materials without impacting their preservation, has been employed for the study of mortars predominantly as a pre-screening technique to identify suitable samples for radiocarbon dating. This study focuses on implementing a recently published methodology based on the calculation of the ratio between the heights of the v₂ vs. v₄ peaks of calcite to distinguish the origin of calcium carbonate in archaeological materials. The research outlines how this methodology proves to be effective not only to distinguish the calcite origin, but also to characterize the binder-related particles and the proportion of pyrogenic to geogenic calcite contained in archaeological binders. Furthermore, the occurrence of changes to the v₂/ v₄ ratio in presence of aragonite – a very common calcium carbonate polymorph – is verified. The present study successfully employs this FTIR application to characterize the binder and binder-related particles of a set of archaeological samples from the Romanesque church of Budeč, Czech Republic; additionally, it emphasises the reliability of the method by testing it on two Roman samples from the site of Nea Paphos (Cyprus) for which the pyrogenic origin was disputed.