Abstract: This experiment analyzes the diffused red in yellowing phenomenon of partial yellow glazed tiles unearthed from Yuanmingyuan by means of optical microscope, EDXRF, SEM, XPS, and XRD in order to study the color change mechanism. The analyses suggest that the glaze layer of the sample tiles belongs to a kind of lead silicate glass and that the diffused red in yellowing phenomenon of glaze is due to the different forms of Fe within the glaze layer, with α-Fe₂O₃ crystal dominating the red area and Fe³⁺ and Fe²⁺ existing simultaneously in the yellow area. The study shows the phenomenon can be explained by the process of oxidation of Fe²⁺ into Fe³⁺ in the yellow area at high temperature during which glaze layers are lost. It further results in abundant precipitation of Fe³⁺ in the form of hexagonal plate α-Fe₂O₃ crystal particle, which is also called micaceous iron oxide red being very important rust preventive and pearlescent pigment.

Key words: Yuanmingyuan, glazed tiles, color change, α-Fe₂O₃