Post-depositional alterations of terrestrial and marine finds of Roman ceramics from Crikvenica production centre (NE Adriatic, Croatia) – A contribution towards chemometric classification

[Display omitted] •Different post-depositional alterations of Roman ceramics from Crikvenica's pottery production were identified.•The effects of seawater, anoxic marine sediments and desalination are recognizable by multi-analytical methods.•Multivariate statistics on FT-IR spectra represent a suitable method for a first screening and identification of representative samples of each sub-group.•Ceramics excavated from the site of the workshop (local ceramics) can be used as a reference group for future classification studies of Roman ceramics from the Crikvenica production centre. Different post-depositional conditions and after-recovery treatments may provoke pronounced physicochemical alterations that can make archaeological ceramics’ classification and comparison difficult even when its provenance is known. The present study describes the differences in the chemical composition verified on sherds of Roman ceramics produced in Crikvenica (NE Adriatic, Croatia). Inductive coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), as well as Fourier transform infrared spectroscopy (FT-IR) were applied to characterise the chemical composition and post-depositional alterations in ceramics recovered onshore and underwater. Chemometrical treatment of ICP-MS results of elemental composition and FT-IR absorption bands was performed using univariate and multivariate statistical tools. Principal component analysis (PCA) led to clear distinction of several clusters of examined samples, i.e. samples from the mainland, samples from the sea bottom, and desalinated samples. All sherds that have undergone desalination represent a distinct sub-group by means of changes in the ratio of accumulated chemical elements. It was established that accumulation of Ca, Mg and Na and formation of salts such as FeS, Mg6Al2CO3(OH)16·4(H2O), and CaCO3 reflect post-depositional environments and post-recovery treatments in terms of desalination and specific marine underwater conditions (oxic and anoxic). Our results outlined a pattern of post-depositional alterations that could be applied in upcoming classification studies. Roman ceramics produced in Crikvenica and excavated from the workshop possess attributes of a reference group, revealing that Ho, Ce, La, Lu, Tb, Gd, Eu and Sm are the elements least susceptible to post-depositional alterations.