https://kknews.cc/collect/96zmepq.html
The article primarily argues that the so called wabi Sabi appearance of many "wood fired" yixing pots are not from wood firing but from reduction firing + addition of various salts.
There is also a part of the article that talks about the fuels used in Yixing during different periods, which is very interesting:
Yixing’s purple clay teapots were basically fired with pine branches in a dragon kiln before the 1970s. At the end of the 1950s, the tail of the dragon kiln was opened and heated with lump coal, and the flame was fired. A layer of clay prevents the flame from directly hitting the teapot, thus ensuring the cleanness and purity of the surface of the teapot. In the past, if there was a fire leak, or if it was accidentally burned to a reduced flame, some fire ignorance would appear. This kind of thing is a defective product and cannot be sold as a genuine product.
Since the end of the 1960s, Yixing Zisha pot kiln was transformed into Suidao kiln, and the original dragon kiln production was abandoned. Due to the energy saving of Suidao kiln, the firing cost of the original dragon kiln was reduced by more than 30%. Therefore, dozens of dragon kilns in Yixing Since then, it has been completely shut down. In the mid-1970s, the fuel was changed from coal burning to heavy oil (slag from refining gasoline), and the cost was further reduced. In the early 1990s, the Taiwanese produced a shuttle kiln (pumping kiln) using liquefied petroleum gas, which was quickly introduced to make purple sand pots, which quickly increased the finished product rate to 98%. In fact, in the 1970s, the Yixing government issued regulations to encourage In the decision document of using coal and heavy oil to burn ceramics, after entering the 1990s, the use of wood-burning pottery was completely prohibited, and it was stipulated in the form of legislation. Liquefied petroleum gas and pipeline natural gas, so far, coal-fired kilns in Yixing have disappeared for nearly 30 years.
Regarding the fake wood firing:
So, where did the so-called firewood come from? In fact, it’s not firewood at all, but a century-old scam. The so-called firewood is just to deceive people who don’t know how to do it. Let’s popularize ceramics here. Kiln firing knowledge. There are two kinds of kiln firing atmospheres for firing ceramics, oxidizing atmosphere and reducing atmosphere.
The oxidizing atmosphere is that the air pressure in the furnace is greater than the pressure outside the kiln, so that the atmosphere in the furnace is very clean, because the impurities and dust outside the kiln cannot enter the furnace, so the surface of the fired purple clay pot is very clean and smooth, and the surface texture of the purple clay pot is natural and beautiful. It is also the standard that people generally require and hope to achieve in the 600-year history of Zisha.
Reducing atmosphere (also called reducing flame) is to adjust the air pressure in the kiln to be lower than the air pressure outside the kiln, so that the air outside the kiln includes nitrogen, inert gas and dust impurities, and even some bad rays can enter the kiln. As a result, a high-temperature reduction reaction occurs in the kiln, and ash falls on the surface of the ceramic product. In order to make the surface of the product more expressive, some industrial salt will be added when the temperature is over 1,000 degrees to liquefy the salt. The mist adheres to the surface of the product and absorbs impurities in the kiln at high temperature, so the fired product shows irregular colors and adheres to different impurities. After the salt is liquefied, a layer of glaze adheres to the surface of the purple clay pot, which makes the purple clay pot lose its color. The double pore structure is changed and it is no longer breathable, which changes the fundamental nature of the purple sand, so that the excellent tea making function of the purple sand pot is no longer.
Burning purple sand pots with a reducing atmosphere to pretend to be firewood is a fraud of the century. It runs counter to the pursuit of the simple, natural and beautiful texture of purple sand, the intangible cultural heritage inheritance process pursued by purple sand pots, and the aesthetic pursuit of purple sand art. Inconsistent, now, some people take advantage of consumers' psychology of pursuing novelty, hype up the so-called firewood purple sand pot, and make it a reason for high prices, and deceive consumers. Such things cannot last for a long time, and they must It has no collection value.