Formula process and coloring mechanism of bluish-white porcelains from the Lanxi kiln in Fujian, China

Bluish-white porcelain was a prominent type of porcelain in ancient China, renowned for its distinctive artistic style and unique characteristics. The Lanxi kiln in Jianning County, Fujian Province, has unearthed a multitude of bluish-white porcelain products from the Southern Song dynasty that exhibit vibrant glaze color and exceptional craftsmanship. The quality of these porcelains surpasses that of contemporaneous Jingdezhen and Baishe kiln products in Jiangxi Province, representing the pinnacle of bluish-white porcelain excavated across various regions of China during the Southern Song dynasty. In this study, samples of bluish-white porcelain from the Lanxi kiln and Baishe kiln, dating back to the Southern Song dynasty, were selected and analyzed via energy dispersive X-ray fluorescence, ultraviolet–visible–near infrared (UV–Vis–NIR) spectrophotometer, metallographic microscopy, and scanning electron microscopy with EDS to investigate their glaze formula process and coloring mechanism. Moreover, these findings were subsequently compared with those of Jingdezhen bluish-white porcelain from the same period. The results demonstrate that the raw materials of porcelain stones used in the glaze of the Lanxi and Jingdezhen kiln are similar in composition yet differ significantly from that employed in the Baishe kiln. Potassium feldspar was added to the glazes of the Baishe and Lanxi kiln, potentially existing exchanges of process of the two kilns due to their geographic proximity. The firing atmosphere of bluish-white porcelain with different glaze colors in the same kiln exhibits significant variations. In particular, the lake blue sample undergoes firing under a strong reducing atmosphere, resulting in an excess content of Fe²⁺ in octahedral hexagon coordination within the glaze, thereby intensifying its blue hue. The colors of various glazes are determined by both chemical color and physical color. The former is a result of the absorption of Fe³⁺ in the ultraviolet region and the d-d electron orbital transition of Fe²⁺ in the infrared region. However, the latter is not the scattering physical color but the diffuse reflection physical color produced by bubbles and anorthite crystallization layers.