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Creative Porcelain Porcelain – Pit fire
From pottery to porcelain, from kiln to kiln, from wood and coal to gas and electricity, over the course of more than ten thousand years of ceramic development, various firing techniques have emerged. Some of the oldest firing methods have even been preserved to this day, evolving into a firing gameplay that combines experimentation and performance. Low temperature, wood burning, enclosed furnace, bonfire It is pit fire.
The ancient ancestors discovered during the process of grilling food with fire that the surface clay under the ashes after cooking was sintered into hard blocks, which taught them how to make pottery for daily life. In some areas of Africa, pottery is piled up in the open air and covered with dry hay and tree branches. After firing, the pottery body shows a black gray color change. Mexico also has a similar burning method, where people stack polished vessels on a “kiln bed” made of firewood, and then cover it with a layer of firewood.
During the burning process, the firewood adds charcoal black color to the surface of the body. During the firing process, wood or other flammable substances are continuously added to ensure a stable temperature rise. This firing method generates a higher amount of heat, and the surface of the green body is darker in black and gray. To this day, the tradition of firing pottery on flat ground is still maintained in countries such as India, Pakistan, Africa, as well as in regions such as Xishuangbanna in Yunnan and Baisha in Hainan, China. The products are not limited to household utensils, but also include sacrificial objects and building materials.
So, what are the steps and precautions for pit burning as a performance burning method?
Part 1
Digging kiln pits/building kiln chambers.
a. Clean an area with a diameter of about 1.8m in an open space, and remove combustible materials such as paper scraps and dead leaves from the surrounding area. The size of the pit is determined by the specifications and quantity of the fired body. For small blank bodies, a square pit with a side length and depth of 60cm is sufficient.
b. If you want to use it continuously on a cement floor, it is recommended to build a pit kiln using red bricks, refractory bricks, or blue bricks. It can be square, cylindrical, or polygonal depending on personal preference.
Part 2
Works firing.
Do not come into contact with thick smoke during the burning process. When stacking fuel in the pit, full consideration should be given to the placement of the billet. Especially the placement of fuel around the billet to prevent sudden collapse and cracking of the billet during the firing process. For safety reasons, the kiln pit should be allowed to cool naturally overnight. A longer insulation time will result in various appearance effects on the outer surface of the billet.
a.Lay a layer of kiln bed at the bottom of the pit using sawdust, ignition materials, and newspapers.
b.The type of burned body determines whether to use a metal grate. The grate prevents the billet from rolling off during the firing process, especially for brittle billets. Placing the grate directly on the fuel at the bottom of the pit not only reserves space for air circulation for the damaged body, but also creates space for ash to fall. The contact surface between the green bodies and the contact surface between the damaged body and the pit wall can only absorb a small amount or no smoke at all. The above characteristics can be utilized to create several “flying white” effects on the blank body;
c.Lay the pit kiln with straw, sawdust, or newspaper. Place some loose straw and newspaper around the blank, and lay a layer of fine sawdust for easy ignition. Spread another layer of straw, newspaper, and coarse sawdust. Continue to sprinkle coarse sawdust until the blank is completely covered;
d.Spread a layer of newspaper and place some ignition materials;
e. Sprinkle a small amount of fuel on the firewood, wait for it to absorb enough oil, and ignite it simultaneously from the edge and center of the pile. If the burning speed is too fast, new fuel needs to be continuously added to the pit, and the open flame continues to burn for 45-60 minutes; And the scorching ashes remain warm for several hours; Burning temperature 550~750 ℃;
f.After about 30 minutes, the firewood turns gray, the flame becomes smaller, or completely extinguished, leaving only hot ash layer by layer extending downwards until the fuel in the pit is burned out. When the firing is nearing its end, you can sprinkle some sawdust into the pit to block oxygen supply and create a reducing atmosphere;
g.Even if there is a one night interval, it is inevitable that there will be unburned hot ash left, so before opening the kiln, it should be ensured that there is no burning fuel in the pit, and the billet should be removed after the kiln pit has completely cooled down;
h.Sprinkle clean water into the pit to completely extinguish the unburned fuel.
Part 3
Cleaning of works.
Some blanks need to be cleaned properly. The cleaning process is simple and convenient, and you can also use it to polish the body. The color spots on the outer surface of the cleaned billet will appear clearer. The appearance of the vessel depends on the type of fuel used during firing, and household cleaning agents are a good choice.
a. Use a hard bristled brush to remove hard lumps and residues attached to the surface of the blank, while also retaining cracks and texture residues;
b.Wipe off the floating dust on the surface of the billet with a wet sponge;
