Temperature-driven phase evolution, microstructural transformation and colour response of Karamay purple clay for Chinese ceramic

Purple clay is a Chinese national intangible cultural heritage. Purple clay is essential for ceramic production, and the purple clay deposits in Karamay, Xinjiang, offer a viable option. This study investigated the effects of firing temperature on the phase composition, microstructure, and coloration properties of Karamay purple clay. Samples were fired at 1040 °C, 1160 °C, 1164 °C, and 1180 °C. Characterization was performed using XRF, XRD, SEM, TGA, and CIE L*a*b* colorimetry. The results indicate: 1. This clay body uses SiO₂ and Al₂O₃ as framework oxides and is rich in Fe₂O₃. As the temperature increases, the mica phase melts into the glass phase, and crystals precipitate, resulting in an increase in the number and size of pores. At 1180 °C, a structure with a raised surface and a porous interior form. 2. Samples below 1164 °C exhibit a reddish-brown color with high saturation; upon heating to 1180 °C.