Topic: Basic Yixing clay 101
<Basic info about Yixing clay>
Clay of Yixing are mainly Jiani, Nenni and Baini.
Jiani is dark solid clay mostly used for making ceramics, vase etc..Nenni is yellow-ish soft clay. Baini is white clay that is mainly kaolinite, used to make porcelain or ceramic.
Zini 紫泥 (purple, fired is usually brown-ish) exists as small amount inside Jiani ore bed. When Zini contains so much manganese that becomes dark dots after firing, it's called Hei Xing ni(aka Tie Xing ni, Hei Xing Sha). Qing Shui ni 青水泥 originally is about method of clay manufactering, pure clay without any mixing, usually mined from mid part of ore bed, common clay. Di Cao Qing 底槽(or曹)青(or清) is from deep inside, usually reddish brown. Di Cao Qing is usually darker and heavier than Qing Shui ni. Pin Zini means mixed Zini.
Luni 绿泥 (aka 本山绿泥 Ben Shan Lu ni, Benshan means original mountain that is Mt. Huanglong) is sort of mutant silica dots, evenly found from Jiani ore bed, very rare. Duanni is also rare, coincidently when co-exists with Luni and Zini. Most Duanni today however, is from Tanxi or Hufu or intentionally mixed with Luni and Zini. Zima(sesame) Duanni has many dark dots that resembles sesame. Bai Ma Zi ni is very similar to Luni after firing but not smooth and lots of grits.
Hongni 红泥 is from Nenni ore bed. Zhuni 朱泥 is very yellow ore, more yellow, better Zhuni. Xiao Hongni is darker than yellow. Da Hongni is from Jiani ore bed, basically Zini. On Zhuni, is special clay cos it has different characteritics than other clay. Unlike other clay(Huang Long mountain), birth place of Zhuni is Zhao Zhuang mountain, which is Lao Zhuni. Zhao Zhuang Zhuni, actually is what you can find from museum. Most of Zhuni today is from Xiao Mei Yao (near Huang Long mt.) and Hu Fu (aka modern Zhuni). Da Hong Pao ni was from Huang Long mt., very popular during Qing dynasty. Real Da Hong Pao ni however, would sell no less than 500 USD. Most of DHP ni is from Fudong area recently.
<On Pin Pei (mixing clay)>
Pin Pei 拼配 can be classified as clay-mixing and chemical ingredient-mixing.
On former one, can actually enhance the quality of clay and plasticity.
Great masters such as Si Da Bin or Hui Meng Chen were actually masters of Bing Pei.
For example, the most expensive clay like Ben Shan Luni can't be used for teapot making without mixing with Zini, unless it's used for decoration. The sought-after clay like Di Cao Qing, is actually better in smoothness and color after mixing with Qing Shui ni or Zini. Pure Di Cao Qing not only requires high temperature (1240C) to be fired but also unglossy and dark. However, Zhuni is exception.
Latter is mixing with ingredients such as manganese oxide, iron oxide, copper oxide etc..
It looks good when first exhibition, but doesn't earn natural patina after long time of usage.
Also, these clays are actually fired at low temperature and smell a lot
<Chemical ingredient-contained clay>
History of this method dates back to ROC.
Due to hazardous effect and need of effectiveness, amount allowed to use limits less than 0.5%.
*Mixing with copper oxide makes artificial Duanni (yellow)
*Mixing with cobalt/chrome oxide makes bright greeness or so-called Muo Luni (墨綠泥)
*Mixing with manganese oxide makes Hei Xing ni(black-star clay), Qing Hui ni(green-grey clay) or Heini(black clay) etc..
*Mixing with iron oxide enhances redness, used for coloring of Zhuni
Chemical used clay mostly doesn't show extra dots of natural minerals but things get more complicated if mixing it with natural clay
<Characteristics of Yixing clay>
Each Yixing clay has a different ideal temperature of firing, different temp has to do with crystallization. Crystallization is important cos it will lead the clay no smell, no blot, better patina and better functioning.
Normal temp of firing is about 1150~1180C, Zini is rather easier clay to treat (Di Cao Qing for exception). Easy to craft, no worrying about firing. Higher temp-fired Zini turns grey-ish purple.
Minimum temp for Luni is about 1180C, lesser temp will lead Luni famous 'blot' or 'crack'. I've seen some sellers recall Luni pots caused by amateur firing. Luni is a clay that has no plasticity, so firing is very complex and requires experience. So to solve this complexity, potters make 'Duanni' by mixing with Zini. Low-temp fired Luni is beige and sees a hint of green after 1200C (Duanni as well).
Normal temp for Zhuni is less than 1100C, Zhuni is of very small particle so sees crystallization at lower temp. Zhuni is a clay that shows highest rate of shrinkage. Normally over 20% and Zhuni is of mud-like clay. That makes working on Zhuni different, should make it quick with less touching. Because more trimmed or touched spot will be reflected after firing. And that's one way to discern a real Zhuni, to find a trimmed or joined spot.
4) Yao Bian (kiln color changed)
Yao Bian pots are not seen often in western market, but is one form of Yixing clay as well. Originally Yao Bian pots were of natural wood-fired effect caused by lack oxygen. Modern day Yao Bian pots are of course from intention. To make this effect, potters fire pots even up to 10 times, or mix among fire-endurable clays and fire up to 1300C, with potters' own method