明代永宣时期景德镇御窑青花瓷“铁锈斑”的显微结构研究

“铁锈斑”,是青花瓷线条色彩浓重处凝聚成的黑色、褐色或带有金属锡光的斑点。作为早期青花瓷器一种典型的鉴定特征，长久以来被认为与使用高铁低锰的进口钴料有关。多年来虽有零星报道，但受到亚微级晶体尺寸、釉熔体不均一性以及元素掺杂、晶体偏析等因素影响，其形态及结构并未得到充分研究，从而导致“铁锈斑”呈色机理不明，其作为进口钴料鉴定标准的观点也遭到质疑。结合前人研究，发现拉曼光谱与扫描电镜能谱仪在古陶瓷微晶结构解析方面极具优势，为系统阐明“铁锈斑”成分结构特征与呈色机理，使用超景深三维视频显微镜、扫描电镜与能谱仪(SEM-EDS)、拉曼光谱仪(Raman)对五件景德镇御窑永宣时期青花瓷器样品中“铁锈斑”处晶体的显微形貌与结构进行解析，并利用激光剥蚀电感耦合等离子体发射光谱(LA-ICP-AES)分别测试样品白釉区域、蓝彩区域与“铁锈斑”区域的成分。显微观察结果表明，不同样品“铁锈斑”区域析晶形态及分布的多样性是造成“铁锈斑”呈现众多视感的主要原因，且同一斑点的析晶区域内伴生有多种形态的晶体。显微结构表明，永乐时期“铁锈斑”枝晶主要以CoFe₂O₄-Fe...

The Microstructure of “Iron Spot” on Blue-and-White Porcelain From Jingdezhen Imperial Kiln in Yongle and Xuande Period of Ming Dynasty

“Iron spot” refers to the black, cyan and brown spots with metallic tin light condensed from the drawing lines on the blue and white porcelain. As a typical identification feature of blue-and-white porcelain of the early Ming dynasty, it has long been considered related to the use of imported cobalt with high-Fe and low-Mn. Although there have been sporadic reports over the years, due to factors such as submicron crystal size, glaze in homogeneity, element doping, and crystal segregation, its morphology and structure have not been fully studied, resulting in the color mechanism of “iron spot” unclear, and the view that “iron spot” as an identification standard for imported cobalt pigment being questioned. Combined with previous research, we found that Raman spectroscopy and scanning electron microscope equipped with energy dispersive spectrometer have great advantages in analysing ancient ceramic microcrystal structures. In order to further explore the composition and structure characteristics of “iron spot”, the ultra-depth three-dimensional video microscope, scanning electron microscope with energy dispersive spectrometer, and Raman spectrometer was used to analyze the crystal microstructure of “iron spot” in five blue-and-white porcelain samples of Jingdezhen imperial kiln in the Yongle and Xuande period of Ming dynasty. The composition of the samples’ white glaze area, blue color area and “iron spot” area was tested by laser ablation inductively coupled plasma emission spectroscopy. The microscopic observation results show that the diversity of crystallographic morphology and distribution in the “iron spot” area of different samples is the main reason for many visual perceptions: the octahedron and its massive aggregate crystals precipitated on the glaze surface present a point-like flashing visual perception; the dendrites that are oriented in parallel and well-developed are prone to the phenomenon of “tin light”; the frosted visual perception is caused by the close arrangement of dendritic and snowflake-like crystals; The excessive development of anorthite forms the raised brown spot to form a network structure. In terms of microstructure, the dendrites in the Yongle period are mainly composed of Mg2+-doped CoFe₂O₄-Fe₃O₄ solid solution, while crystals in the Xuande period are mainly MnFe₂O₄-Mn₃O₄ solid solution doped with Mg2+ and Co2+, and associated with reticulated anorthite. The above results show that an “iron spot” can be formed on blue-and-white porcelain fired with imported or domestic cobalt pigment. Since the crystals formed are all cubic inverse spinel structures, they have a certain similarity in macroscopic morphology. To sum up, this study clarifies the microstructure and composition characteristics of “iron spot” on blue-and-white porcelain from Jingdezhen imperial kiln in the Yongle and Xuande period of the Ming Dynasty. It reveals the coloring mechanism of “iron spot”, which provides a certain scientific basis for the identification of blue-and-white porcelain in Jingdezhen imperial kilns, and also provide some reference for the application of Raman spectroscopy and scanning electron microscopy spectroscopy equipped with energy dispersive spectrometer in the analysis of complex microcrystalline structures of ancient ceramics.