Non-Destructive Analysis of Preliminary Study Ceramic Materials Unearthed at the Iznik Tile Kilns Excavation Using Portable XRF and Raman Spectroscopy

Abstract

In this study, 20 ceramic sherds produced as part of technological experimentation by ceramicists were examined using optical microscopy, Raman spectroscopy, and a portable handheld X-ray fluorescence (pXRF) spectrometer. The samples are coated with a transparent glaze and decorated on both sides with underglaze, brush-painted lines in different colors. The aim of the study was to characterize the chemical composition of the ceramic body, colored areas, and glaze by pXRF, and to identify the molecular structure of the glaze, mineral phases in the body, and pigments in the colored areas by Raman spectroscopy. The investigated colors include green and turquoise hues, various shades of blue and red, and black outlines. Microscopic examination revealed glaze thicknesses ranging from 102 to 421 µm, with several samples thinner than 200 µm, notably below those reported for tiles. Slip layers vary from quartz-rich white to clay-rich beige compositions, often contrasting with the underlying body color. pXRF analyses confirm the predominant use of a stonepaste body recipe, characterized by high quartz and low alumina contents, except for one clay-rich sample. The glazes are mainly lead-rich (22–40 wt% PbO), with a single low-lead exception. Tin oxide occurs only in trace amounts, consistent with late 16th–17th-century Iznik productions. Variations in CaO–K₂O flux compositions indicate experimental glaze formulations and diverse raw material sources. Overall, the results suggest experimental productions from Iznik workshops, likely dating to the 17th century, focused on exploring color hues and glaze variability before the standardized manufacture.