This week’s blog entry is Part 2 of our series on processing Tian Qing Ni. This week we look at the steps taken from clay to finished teapot.
Sky Blue Clay
After being shaped by the potter, Tian Qing Ni teapots go through the same final steps in production as other Yixing Teapots. They are first left to dry out thoroughly before being fired in the kiln. "Tian Qing Ni" can be translated as azure or sky-blue clay. It might seem like a strange name for a clay that is perhaps best described as being “dark liver" in appearance in finished teapots. The name makes more sense when you see the raw ore and unfired clay.
Tian Qing Ni Teapots drying out before being fired in the kiln appear blue-grey in colour:
Before firing the first batch of teapots, Lin fired a series of clay discs to test the effects of firing at different temperatures. He consulted available information about the firing range of the clay.
Lin Hanpeng fires his teapots twice. During the first firing the clay will shrink by a certain amount. Lin will remove the teapots, check to see the effect of the shrink rate on lid fit, make adjustments if needed, then fire the pots for a second, final time. Teapots are fired twice to ensure a tight lid-fit.
The firing guidelines in most of the literature, including from the book 阳羡茗砂土 show the results of firing the clay a single time at different temperatures. 阳羡茗砂土 discusses a firing range between 1170-1210°C. Lin found that firing Tian Qing Ni twice at a temperature of 1182°C produced similar results to firing the clay once at 1200°C. Lin also experimented at different temperatures between 1170-1200°C and found that firing at a lower temperature produced finished clay that was too light in colour, and firing at higher temperatures produced a clay that looked “overcooked.”
With the results of the test firings in mind, Lin decided to fire his Tian Qing Ni teapots at 1182°C.