“Internal cracking,” “external cracking,” and “cloud disk” are issues that occur during the making of purple Clay Teapots, commonly seen in ribbed designs. Why is this so?
Because ribbed designs have a distinct concave and convex profile, where the “ribs” act as the “bones,” representing the contracting force; the “cavity” represents the “breath,” showing the bulging force. The requirements for a ribbed-cavity Teapot are: both the inside and outside of the teapot should feature ribs and cavities; the rib and cavity formations must be lively and smooth; the ribs and cavities on the lid and mouth of the teapot must correspond and connect tightly. This combination of convex and concave profiles can lead to cracking due to the sandy nature of the clay, resulting in “internal cracking” and “external cracking.”
Internal cracking refers to cracking on the inside of the teapot. If you purchase such a teapot, you may not notice it at first, but when brewing tea in winter, the sudden temperature change might cause a thermal shock, leading to a crack. This is one reason why thermal shock cracks often occur in purple clay teapots during winter.
In the full-Handmade process for ribbed design teapots, the maker shapes a round body tube and then uses tools like “ribbers” and “lining ribs” to press lines into the body tube from both inside and out, repeating the pressing until the surface is smooth, round, and full. The pressing is done from the outside inward, and if not handled properly, it can easily cause internal cracking, known as “internal cracking.”
External cracking, as the name suggests, refers to cracking on the outside of the teapot. This phenomenon is more likely to occur in semi-handmade ribbed design teapots. Semi-handmade production involves using molds and then burnishing the clay inside the mold, with the pressure applied from the inside outward. This can easily cause cracking between the ribs on the exterior, known as “external cracking.”
Cloud disk is a situation frequently encountered by new teapot makers. After painstakingly crafting a teapot and leaving it in a cabinet to naturally air-dry before firing, they may discover a ring of cracking on the bottom inside the teapot. This is known as “cloud disk,” which occurs due to poor bonding between the body tube and the base piece. The primary reason is insufficient mastery of the clay's properties and improper control of its moisture content.
The above describes these three types of cracking phenomena.
Images: Tea Nest Network
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