“…Carbonate vibrations at 1794, 1430, 876, and 712 cm −1 are absent, suggesting the use of purified clay with low limestone content and high firing temperatures [21]. Smaller signals belonging to quartz (1164, 1086, 795, 781, 694, 449 cm −1 ), hematite (596, 529 cm −1 ), kaolinite (439 cm −1 ), and feldspars (1053, 729, 721, 645, 606, 589, 581, 464 cm −1 ) were individuated by using second derivatives [34], confirming the Raman spectroscopy results. The presence of hematite may indicate an oxidizing atmosphere in the kiln.…”