Formation mechanism of the pinholes in brown glazed stoneware from Yaozhou kiln

Abstract

Pinhole is a common defect widely seen in many archeological stonewares from different kilns and periods. It is usually a sub‐millimeter pit on the glaze that was believed to be caused by the broken bubbles during the firing process. We investigated the pinholes on a porcelain sherd from Yaozhou kiln of the Song Dynasty (AD 960–1,127), surprisingly, every pinhole corresponds to a flower‐like cluster observed through the microscope. The flower‐like clusters are composed of radial mullite whiskers and ε‐Fe2O3 dendrites, and its growth mechanism were proposed after detailed microscopic and spectroscopic characterizations. The unique chemical composition around the pinholes became the breeding ground for the crystallization of flowers, whereas the crystallization process further facilitates the formation of the pinhole preventing the glaze from restoring smoothness. Our results enriched the knowledge on pinholes and revealed the interesting crystallization assisted formation mechanism, which not only related to bubble rupture but involves the crystallization dynamics as well.

Microstructure analysis of “iron spots” on Qinghua porcelain from Jingdezhen imperial kiln

“…The developed dendrites with directional parallel branches tend to form the "tin light" spots. It is quite similar to the Fe2O3 crystals of "oil spot" in the Jian ware and brown glaze in Yaozhou kiln in which crystals are organized in a 2D periodic fashion [31,39]. Frosted spots (black, brown, and gray foggy spots without glitter) are mainly caused by dense dendritic and snowflake crystals from the nano to micron-scale with irregular configurations.…”

Recycling of granite sludge for the preparation of high‐strength glazed glass‐ceramics using stepwise sintering

“…With the instantaneous glaze firing at 1300°C, the sintered glass‐ceramics was light yellow in color (Figure 12A). Although the surface glossiness was 61.6%, there were a few pinholes on the surface glaze, which are closely related to oversintering and iron‐bearing impurities 32,33 …”

“…Although the surface glossiness was 61.6%, there were a few pinholes on the surface glaze, which are closely related to oversintering and iron-bearing impurities. 32,33 To overcome these problems, the pickling powder was used for the instantaneous glaze firing at a heating rate of 50 • C/min at 1300 • C. In this case, the glaze color changed from light yellow to milky white, and the glaze pinholes were completely eliminated. The flexural strength and surface glossiness of glazed glass-ceramic correspond to 112.5 MPa and 54.7 GU, respectively, far superior to those of bright glazed tiles in the market (>16 MPa and >45 GU).…”