Iron Spotting (铁熔)

Iron spots (铁熔, tie rong, “iron melting”)[2] are black speckles visible on the surface of fired Yixing wares. The dark speckles may be raised or flush with the skin of the ware. Tie rong are formed from magnetite (Fe₃O₄) particles[3], with larger particles forming more prominent speckles. Magnetite is naturally present in certain zisha ores at various concentrations, and may also be formed when zisha material is exposed to a reduction atmosphere during firing[4]; high iron wares are thus partially more likely to develop iron spotting[5].

Iron spot speckles are usually small in size and randomly distributed throughout the surface of the ware; it is generally held that a few well distributed iron spots do not constitute a flaw, as their presence is very common and difficult to prevent. Dense clusters of iron spots, large iron spots formed through the fusing of an iron spot cluster, and defuse dark discolorations from iron spots directly under the skin of the ware are (generally) considered flaws in Yixing wares, though certain zisha clays are known for their speckled pattern formed from iron spotting[6].