Firing pottery requires a stable temperature. As for drying pottery, in addition to temperature, maintaining the overall humidity of the pottery is also a crucial factor.
I carefully placed the base pivot into the hollow mud pile, and then completely blocked the opening with a raw twig, so that the moisture inside could only be released slowly and would not dry out all at once.
Next, I piled a ring of dry firewood about 20 centimeters away from the mud pile and lit it. I used the heat radiation from the firewood to slowly dry the kaolin clay spool inside the mud pile.
This method is somewhat similar to the method of making beggar's chicken. With the support of flames from all 360 degrees, a large amount of white steam pours out from the outlets around and on top of the mud pile.
Because the top is blocked, moisture can only slowly escape through the gaps in the growing branches, while most of it still relies on the outer wall of the mud pile to dissipate.
I have to admire the old man; his method of using semi-dry mud to evenly absorb moisture is truly ingenious.
The water absorption of a material is also determined by its saturation level. Soil is a naturally porous water-absorbing material. When heated in a semi-dry and semi-wet state, it will generate a high-temperature and high-humidity air inside.
Don't underestimate this seemingly insignificant moisture; it's crucial in protecting pottery from sudden temperature changes and the cracking caused by thermal expansion and contraction.
It's like how an inert gas is needed inside a light bulb to protect the filament from burning out.
But the intricacies go beyond that. It not only protects the pottery, but also exchanges moisture with the clay body, allowing the internal humidity of the clay to dissipate through the outer wall, achieving a consistent and constant effect.
This process minimizes the effects of thermal expansion and contraction. Compared to natural air drying, this method will definitely yield a higher success rate for pottery.
My base bearings aren't very large, so after a short distillation process, the outer wall of the clay began to turn white and dry, which was a sign that the humidity inside was decreasing rapidly.
After burning for a while longer, even the branches used to seal the opening turned charred black, clearly indicating that they had dried out completely.
I let the fire die down slowly on its own, allowing the temperature to drop.
While I was waiting, I didn't sit idle. A kiln built with stones and mud was completed. Considering that I would need to use it many times in the future, I decided it would be better to make it sturdy.
The configuration of the earthen kiln is similar to that of the one I had in my hometown, but this time I decided to make some slight improvements to the air inlet of the earthen kiln.
While using a siphon method for air intake is good, the airflow is still insufficient when smelting iron, requiring manual assistance from the automatic air intake system.
However, I don't plan to make any blowers or bellows. Those things are either hand-cranked or require spending more time developing a hydraulic system to replace manual blowing.
Although both work follow the law of conservation of energy, why should I spend so much time working?
I always pay close attention to the return on investment; only things that can create the greatest value in the least amount of time are worth doing.
Therefore, the approach still needs to use a siphon system for automatic ventilation, but this time the system needs to be upgraded.
We need to take it out separately and create a custom-made "engine" for it.
At this point, only embers remained of the fire beside the mud pile, and most of the heat had dissipated.
I went to the mud pile and took out the base bearing. Apart from some carbon black on the surface, I didn't find any cracks. The dryness was also good. It was already hard to the touch.
This bearing plays a very important role and needs to be fired first.
I just need to modify this dried mud pile a little using the method the old man taught me, and it can be used as a small kiln.
The specific method involves adding a small pile of dry grass into the hollow mud mound, just like before, to create an inverted cone-shaped structure. Then, mud is applied to the inside, and the dry grass is burned away to create a new hollow.
A porous kiln bridge cover made of clay is needed on top so that the shaft can be placed stably on the road bridge to be fired into pottery.
This time, the fire was started using the cone-shaped cavity inside, which was just big enough to hold the firewood. The top of the mud pile outside needed to be sealed with a suitable stone slab, leaving only a small vent for smoke to escape.
When the cone-shaped structure below is fired, the temperature inside will continuously rise, reaching a maximum of over 800 degrees Celsius, which is the upper limit that low-temperature firing kilns can achieve.
The hardness requirement for the shaft is not very high. Even if all the clay blanks are placed on it, the maximum weight is only a few dozen kilograms. The shaft of this firing process can withstand at least 300 kilograms of pressure without breaking.
Larger porcelain pieces probably wouldn't need a turntable; other techniques would be required. However, I doubt it would be necessary, as this thing is too heavy and impractical for me.
I put the base axle in and started firing the kiln. Since it was only a few steps away from my main kiln, adding firewood was very convenient.
After adding a few more bundles of firewood, I moved on to this other task. I had just mentioned focusing on improving the stove's siphon system, which meant I needed to build a separate stove.
In order to make it multi-purpose, I also decided to turn it into a large pot for stir-frying and boiling water, so that I can stew any large poultry ingredients in one pot in the future.
This reminds me of the braised goose in an iron pot in Northeast China. Of course, the pot is available, but it would be even better if we could also have some swans from my hometown.
The siphon-type stove is key to the blower power, while firewood is the fuel that powers the machine. How to use fuel more efficiently to drive the machine depends on its structural design.
I still started by building a rough shape of a furnace with stones and mud, but the firebox of this furnace was larger than that of a kiln, and the air inside the furnace could be at least three times that of a kiln.
To enhance the blast effect of the refining furnace, the furnace itself only has an exhaust port and no air intake design.
Even after adding firewood, a stone slab would be used to block the firewood inlet to prevent air from entering directly through it.
The secret to air intake lies in that short section of four-way return air duct connected to the furnace.
Between the air outlet of the kiln and the air inlet of the siphon stove, I made a mud ventilation pipe with a diameter of about 50 centimeters and a length of about half a meter.
The design incorporates a siphon ratio of 3:1, which is optimal for the ratio of exhaust vents to air inlets in the furnace. At this point, the internal space of the stove is three times that of the furnace, resulting in an air exchange rate that is also approximately three times higher.
At this moment, the exhaust vent of the kiln forms the optimal siphon ratio of 3:1 for the stove's air inlet.
Because there is only one air inlet in the kiln, it is connected to the air inlet and exhaust outlet of the kiln and the air inlet and exhaust outlet of the stove by the four-way connecting pipe.
At this moment, just like a gear, the furnace's three-fold air intake speed is increased by two times after being amplified by the stove, reaching a six-fold siphon air intake speed.
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