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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. [ABSTRACT FROM AUTHOR]