# Formation Mechanism of Crystal Spots in Jian Kiln Oil-Spot Glaze Revealed by Simulation Experiments
## 4 Conclusions  
This study successfully replicated the Chinese Jian kiln oil-spot glaze porcelain using a rapid air quenching method at critical temperature points during the firing process to preserve its high-temperature state, resulting in a series of samples. Microscopic structure and phase analyses of key samples were conducted using scanning electron microscopy, laser Raman spectroscopy, and photoelectron spectroscopy, revealing the formation process and mechanisms of the oil-spot glaze crystal spots in the Jian kiln. As the temperature increased to approximately 1220 \({}^{\circ}\)C, the iron oxide in the glaze underwent significant decomposition, producing bubbles that migrated and enriched the iron-rich particles at the glaze surface, resulting in a saturation of iron content that provided a material basis for subsequent crystallization. Under the influence of a high-temperature reducing  
Figure 8: Schematic diagram of the formation process of oil-spot glaze crystal spots in Jian kiln.  
atmosphere, the viscosity of the glaze melt decreased, the decomposition rate accelerated, and bubbles rapidly migrated outward, promoting the precipitation of Fe\({}_{3}\)O\({}_{4}\) nanocrystals at the glaze surface and the formation of small crystal spots. Under the influence of surface tension, these small crystal spots gradually aggregated to form larger ones. As the kiln naturally cooled, the atmosphere inside gradually transformed into an oxidizing environment, leading to the oxidation of the glaze surface. At approximately 1150 to 1180 \({}^{\circ}\)C, the Fe\({}_{3}\)O\({}_{4}\) nanocrystals within the crystal spots transformed into lamellar \(\epsilon\)-Fe\({}_{2}\)O\({}_{3}\) crystals. As the lamellar \(\epsilon\)-Fe\({}_{2}\)O\({}_{3}\) crystals continued to grow, external iron sources migrated into the crystal spots, ultimately resulting in a yellow-brown or reddish-brown appearance within the spots, while the exterior appeared black.  
Although this study has achieved some preliminary results, it has important implications for the development of high-temperature iron-based crystalline glazes with varying color effects. We also hope that these findings will inspire further research and contemplation on ancient Chinese high-temperature iron-based crystallization glazes. During the research process, we made many interesting discoveries, among which the most noteworthy is the rich variation in the color effects of the glaze during the cooling stage. Future studies could implement corresponding adjustments to the cooling regime (cooling rate and even the atmospheric conditions during the cooling stage), which is expected to yield different color effects on the glaze surface.  
Conceptualization, J.W. and J.Z.; methodology, J.Z.; validation, T.L. and K.L.; resources, Q.B.; writing--original draft preparation, C.J.; writing--review and editing, C.J. and J.W.; supervision, J.Z. and J.W.; project administration, J.W., T.L. and C.J. All authors have read and agreed to the published version of the manuscript.  
This work was supported by National Key R&D Program of China [2023 YFF0905800], Major Program of Jiangxi Provincial Social Science Fund [JD18050], and the Jiangxi Provincial Postgraduate Innovation Fund Program [YC2024-B246].  
Not applicable.  
The original contributions presented in the study are included in the article. Further inquiries can be directed to the corresponding author.  
The authors declare no conflicts of interest.