Tian Qing Ni: From Raw Ore to Clay
(Originally published March 9, 2020)
Now that the first batch of Tian Qing Ni Yixing Teapots has emerged from the kiln, we decided to write a short follow up to last October’s article, this time discussing the steps in the process for turning raw Tian Qing Ni ore into usable clay for teapots. Tian Qing Ni is a rare subcategory of purple Yixing clay (zini), prized for its beauty, ease of shaping and firing, and for improving the flavour and aroma of tea.
While the steps below show Tian Qing Ni, the same process can be applied to any kind of zini. Photos are from Lin Hanpeng’s studio where the process took place.
Raw Tian Qing Ni ore.
Step 1: Weathering
Large pieces of raw Tian Qing Ni ore is left outside, exposed to the elements. These large chunks break up into smaller pieces. Weathering is the first step in processing the ore and is said to increase the plasticity of the clay.
The pieces of ore are spread out under the sun. The ore is examined and pieces that are “unpure” (containing other elements besides Tian Qing Ni) are removed.
After baking in the sun for a time, the pieces of ore are sprayed with water. This causes the ore to break up again into smaller pieces.
3) Baking in a pile
The wet ore is pushed into a pile and a tarp is placed over top. The ore is said to be “baking in a pile.” The water soaks into the ore and the tarp prevents it from escaping. The sun over the tarp heats up the pile, “baking” the ore in a high humidity environment.
4) Air Drying
The tarp is removed. The ore is spread out with a rake and left to dry out in the open air. After the ore has dried, it is collected and brought inside.
Step 2: Milling and Sieving
1) Cleaning the tools
All tools are cleaned thoroughly to prevent contamination from other elements or clay.
2) Milling the ore
A bucket with a hole is placed on top of the clay mill. Some bamboo sticks are stuck into the bucket to stabilize it. The weathered ore is then poured into the bucket where it is drawn down into the mill and crushed into powder.
3) Sieving the ore
The clay is sieved for the desired grain size. Larger pieces are removed from the top of the sieve to be milled again.
4) Removing Iron
Any grains larger than 80 mu need to be “de-ironed”. If this isn’t done, there is a risk of large unsightly iron spotting in the finished clay. A magnet is moved over these large pieces to detect iron. Magnetic pieces are manually removed. It is normal and to be expected that small amounts of iron remain in the clay and can be visible on very close inspection in the clay of fired teapots.
Step 3: Mixing
There are two reasons for mixing the clay. The first is to ensure the larger grains are mixed evenly with smaller grains. The second is make sure the water is evenly mixed into the clay. Lin Hanpeng prefers to mix all of his clay by hand rather than using a machine. By mixing by hand, he is able to tell when the clay is ready and what the consistency and texture are.
After mixing, the clay is placed into bags and stored for 10 days.
Step 4: Sealing and Ageing
After the clay has been mixed and left to sit for 10 days, the clay is taken and shaped into slabs. The slabs are placed into plastic bags and vacuum sealed. The sealed slabs are stored in the studio for ageing. After ageing for months or years, the clay is removed and ready to be shaped into teapots for firing. This batch of Tian Qing Ni was aged for around 6 months.