These crackles, which resemble spider webs or icebergs, were once considered firing defects of porcelains, resulting from quickly cooling glaze. Until the Song Dynasty (960-1279), masters at the famous Ru Kiln, one of China's Five Great Kilns, learned to control the density of color of crackling and began to create the effect on purpose.
Video provided by www.theworldofchinese.com
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