A Teapot enthusiast asked a few days ago, “Why are purple Clay teapots called such?” What exactly does the term “clay” refer to, and what role does it play in a purple clay teapot?
1: What Exactly Does “Clay” Refer To In Purple Clay?
1. Quartz particles (as shown by the white dots in the image below). This is according to the academic school of thought;
2. The physical cohesion of purple clay, as per the experiential school of thought.
When discussing with others, it is essential first to clarify which concept is being referred to; otherwise, heated debates can ensue, with the experiential school thinking the academic one knows nothing, and the academic school viewing the experiential one as ignorant. The “double-pore structure” of purple clay is closely related to its quartz content. The “purple” refers to color, while the “clay” refers to its nature.
When a purple clay teapot breaks, you can examine its fractured surface to clearly discern its unique structure. During firing, carbonate in the clay decomposes, releasing carbon monoxide and carbon dioxide gases that form bubbles. Some of these bubbles connect, forming an open “chain-like pore cluster,” while others remain isolated within aggregates of quartz and silicate particles, blocking any interconnections and creating a closed system. The coexistence of open and closed pores is known as the “pore-void structure,” commonly referred to as the “dual-pore system.”
Observing the fractured surface of a fired purple clay teapot reveals open pores between aggregates, through which gases can pass, and closed pores within the aggregates, which obstruct Water flow.
Due to the surface tension of tea, liquid cannot penetrate through these pores to the surface of the pot. However, since gas molecules are much smaller than water molecules, steam can escape through the pores. This is the well-known property of allowing air but not water to pass through, a unique characteristic of purple clay teapots.
2: What Role Does the “Clay” Play In Purple Clay Teapots?
(1) Decorative function, exemplified by the application of sand (mature sand) technique.
This is somewhat akin to sprinkling sesame seeds on a bun. Sesame seeds on a bun make it tasty; “sesame seeds” on a teapot make it visually appealing. However, the application of sand technique should not be overused. If improperly executed, it can detract from the natural style of a purple clay teapot.
If the distribution of sand is too regular or too random, it will not enhance the Beauty but rather mar it. As shown in the image below, the Purple Jade Golden Lozenge Teapot is clearly more aesthetically pleasing.
(2) Raising the firing temperature to achieve desirable coloration.
Color and degree of vitrification are a pair of contradictions in the making of purple clay teapots. At a certain temperature and under a specific firing atmosphere, purple clay will exhibit a specific color.
However, even if the color is excellent, if the teapot is not fully vitrified, it cannot be considered finished, as a purple clay teapot must meet practical requirements: it must allow air but not water to pass through and have sufficient body strength (not easily breakable).
The addition or reduction of sand plays a critical role here. Increasing the firing temperature requires adding more sand; lowering the temperature necessitates reducing it.
Source: Purple Clay Teapots
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