How is the teapot fired?

It is the art of earth and fire, and the material of pottery is the basis of the characteristics of finished products and the body of the vessel; Firing is the stage that determines the effect of finished products. Good purple sand and proper firing technology can make clay present the most perfect green body after firing. Needless to say, there are only two factors that have a decisive influence on the firing effect of purple sand: temperature and atmosphere. Temperature mainly affects the sintering degree, and atmosphere mainly affects the color rendering effect. Different from clay, purple sand has more kinds of internal substances than clay, and its most prominent feature is that it contains timeliness. Clay is either not sintered like pottery or completely sintered like porcelain. It is almost impossible to completely transition between unsintered and completely sintered like purple sand, because the melting points of different components in purple sand are different. Reasonable use of this transition period is not only the time and space to make a big fuss about the firing process of purple sand, but also the opportunity to make the finished purple sand more brilliant. Metals and their oxides are the only colored substances in purple sand. The same metal composition will generally produce different oxides under different conditions, and these oxides have different colors, which is why the same clay will have different colors after firing. Some substances, under certain conditions, will lead to the formation of different oxides. Some of these substances exist in mud and some in reaction environment, mainly oxygen, carbon monoxide and carbon dioxide. They play the role of oxidant and reductant in the firing process of purple sand. There are three variables in temperature: height, changing speed and temperature difference between inside and outside, which also have a decisive influence on the firing effect of purple sand. Atmosphere is the space where chemical reaction takes place during firing, and it is the concentration of oxygen and carbon monoxide. Oxygen, basically foreign, carbon monoxide, mainly comes from fuel, and a small amount comes from the chemical reaction of some components in mud. At present, kilns that burn purple sand are basically electric kilns and liquefied gas kilns. Coal kilns that mainly burn daily-use pottery and Qianshulong kilns that burn coal and firewood can also burn purple sand pots. Electric kiln, which is electrified and heated by metal resistance wire in a closed space, is characterized by constant oxygen content (the content of the space in the kiln when charging the furnace), slow heating and cooling, balanced feeding temperature inside and outside the blank (but the position difference may be large, the large electric kiln can reach more than 30 degrees) and accurate temperature control. Because the firing is completed in a closed environment, there is no oxygen supplement during the firing process, and the carbon monoxide released from the green body cannot be discharged, so the firing atmosphere is generally weakly reducing (the fired products are placed in an open position). Liquefied gas kilns are mainly push-plate kilns, which are shaped like tunnels. It is driven by a hydraulic press, and both ends are always open during the firing process, and the middle section is the combustion zone. The combustion substance of liquefied gas is also carbon, so carbon monoxide will also be produced during the combustion of liquefied gas, which will be mixed with oxygen coming in through two openings to form a combustion atmosphere. Saggers made of refractory materials must be put into the pusher kiln first, and the saggers are placed up and down, so that a stack of saggers can only open the upper layer and the lower part is closed and semi-closed (saggers are slotted). The length of the whole kiln, the length of the combustion zone, the size of the remaining space at the openings at both ends, the purity of liquefied gas, the injection amount of liquefied gas, the placement mode (open or closed) and the placement position (up and down) of the sagger are all variables that affect the firing effect of the pusher kiln. Liquefied gas kilns also have shuttle kilns, which are similar in shape to large electric kilns, but the heating mode is not electrified by resistance wires, which leads to the difference between shuttle kilns and electric kilns mainly in the firing atmosphere and heating (the surface of the fired product ejected by the flame will have a higher temperature). In the past, coal mines were mainly inverted smoke kilns, which were similar in appearance to yurts and had circuitous fire paths to increase the flow of firing space. The position temperature difference is large and the controllability is low. The biggest feature comes from burning coal. If the sulfur content of coal is high, it will make the surface of teapot form pink and khaki flowing composition effect, which is very strange. The most changed is the firewood kiln, which is also the Qianshulong kiln. This is also the most traditional firing method of purple sand, so the finished product has the characteristics of an ancient pot. The firing of Qianshulong kiln has the most variables, because there are 24 pairs of holes on both sides of the kiln to watch the fire and throw firewood, so the weather has a unique influence on the effect of the finished product. Air pressure, temperature, air humidity, wind direction and wind force will all have an impact on the discharge effect. Coupled with the joint action of variables such as firewood quantity and firewood throwing mode, it is the most uncontrollable, unpredictable, uncertain and extremely risky. Kiln burning costs are also high. In addition, the firing technology only talks about experience, not science, and it is extremely rare that only Longyao can fire the teapot. Qianshulong Kiln is now a state-level cultural relics protection unit (which can only be protected). Because of its reputation, it is not uncommon to see cottage kiln works on the market now. Kiln change is the formation of different redox atmospheres on the surface of small teapot, which leads to the formation of metal oxides of different colors on the surface of teapot. Electric kilns, push-plate kilns, shuttle kilns and inverted smoke kilns can't burn at all, because these kilns can't form two completely different atmospheres of oxidation and reduction in the space of a single teapot. The same work, fired in different kilns, will have different effects. It is better to burn "water color" in electric kiln than push plate kiln, shuttle kiln, inverted smoke kiln and open flame dragon kiln, but the works of open flame kiln have rough surface when they leave the kiln, and there will be "fire thorn" phenomenon. This is because the local temperature at the top of the flame is high, and the purple sand particles on the surface of the blank will burst because of the high temperature. But it is precisely for this reason that the soaking effect of electric kiln firing works is not as varied as other types of kilns.