The furnace cooling indicator light turned from red to green. Chen Hao stepped forward and flung open the side door.
The heat, carrying ash, hit his face. He squinted and reached in, carefully lifting the T-01 pottery jar out. The jar was entirely brownish-black, with a thin layer of glaze on the surface, and it looked quite authentic.
"Done?" He grinned. "My first piece of art, do you want my autograph?"
Nana didn't reply, but took the jar he handed her, ran her fingertip lightly along the rim, then turned it over and carefully examined the seam at the bottom against the light.
Click.
A soft sound, so faint it was almost inaudible, but the two of them stopped at the same time.
A crack climbed diagonally upwards from the bottom corner, running through a third of the can body, as if someone had used a needle to scratch the sintered layer.
"Uh... thermal expansion and contraction?" Chen Hao scratched his head. "How about we reheat it? To reinforce it?"
“Secondary sintering will exacerbate structural disintegration.” Nana put down the jar and took a magnifying glass from the tool rack. “The cross-section shows a stepped fracture, indicating that the internal stress was not released evenly. The clay shrinkage rate exceeds the standard, and hidden cracks were already formed during drying. The firing process only makes them visible.”
"So...the problem with the mud?"
"yes."
Chen Hao stared at the crack, somewhat incredulous: "But I dug this soil myself. On the east slope, the soil sticks to the soles of your shoes when you step on it. It should be sticky enough."
“Strong viscosity does not mean it is suitable for firing pottery.” She pulled up the data board. “The plasticity index barely meets the standard, but the particle size distribution is poor and the sand is unevenly distributed. During sintering, the shrinkage rate of different areas is not synchronized, which will inevitably cause cracking.”
"Then what should we do? Mix in something else?"
"The knowledge base suggests adding skeletal materials to reduce the overall shrinkage rate. Fine sand, rice husk charcoal, or crushed ceramic slag can be used."
“It’s ready-made.” Chen Hao turned around, opened the cabinet, and took out a bag of sifted river sand. “I even dried it in the sun for three hours yesterday, so there’s no dampness at all.”
For the next half day, the workshop was filled with the sounds of kneading clay, stirring, and Chen Hao humming a little tune.
New recipe: three parts raw clay, one part fine sand, add water and mix well, knead until your arms ache. As he stirred, he muttered, "This isn't pottery making, it's health maintenance—building arm strength."
In the second round of clay shaping, he was extra careful this time. He pressed the outer wall with his left hand and supported the inner cavity with his right hand. The turntable turned slowly, and the clay lumps rose little by little, with the rim becoming rounder than the last time.
"How's it going?" He wiped his sweat. "Does it look like a proper jar now?"
Nana nodded: "The appearance is acceptable, proceed to the air-drying process."
They placed the t-02 on a ventilation rack, covered it with a damp cloth, and controlled the humidity to slowly dehydrate it. After 24 hours, the clay hardened, turned dark gray, and felt cool and dense to the touch.
The second time the kiln is filled, the temperature rise curve is smoother, increasing by fifty degrees every half hour, with heat flow distribution monitored throughout the process.
When the food came out of the oven, Chen Hao held his breath and waited for the results.
This time the tank was intact, without any major cracks, but when he took a closer look, he frowned.
"Why... are they all in circles?"
The jar is covered with fine, circular cracks, like tree rings or a dried-up riverbed. They are not deep, but they densely cover the middle and lower parts.
“Temperature fatigue lines.” Nana touched the surface lightly with a probe. “The outer wall cools down quickly, while the inner layer is still shrinking, creating shear stress. This indicates that the material’s resistance to deformation is insufficient, and even adjusting the process cannot eliminate the defect.”
"So, no matter how much you mess with it, as long as it's still this soil, it'll crack sooner or later?"
"The conclusion is valid."
Chen Hao plopped down on a small stool, looked up at the tin roof, and sighed deeply: "I thought making a jar would only take a little effort, but I didn't expect that even the soil had to be picked and chosen. How did people in ancient times survive without so many instruments?"
"Early pottery was mostly fired in open-air piles, resulting in an extremely high failure rate. Archaeological records show that less than 20% of the pottery unearthed from the same site is intact."
"No wonder people didn't like to store things back then. They probably would break as soon as they stored them, so they just prepared only what they needed."
He stood up, walked to the waste bin in the corner, and threw the T-02 in. With a crack, the can shattered into several pieces.
“One more time,” he said. “Try a different additive.”
This time, he dug out the pottery shards that had been burned last time, smashed them into powder with a hammer, and mixed them into the mud as crystal nuclei; for the third attempt, he added half a spoonful of rice husk ash, saying that he was imitating the ancient method of "carpentry pottery".
When T-03 came out of the oven, its surface was much smoother, and it made a crisp sound when tapped. Chen Hao almost thought that this time it was a success.
On the morning of the third day, he discovered that a small piece had chipped off the edge of the jar, and a crack extended from the inside, as if it had been forced open from the inside by something.
"It... cracked by itself?" He stared wide-eyed.
“Microcracks went unnoticed during the later stages of drying, but fluctuations in ambient humidity induced the fracture.” Nana examined the fracture surface and said, “The material’s refractoriness was insufficient, and the degree of sintering was inadequate, making it impossible to form a stable silicate network.”
She pulled up a comparison chart: three curves side by side, representing the shrinkage rate, porosity, and compressive strength of the three tests, respectively. All hovered around the warning line; none met the standard.
"In summary: the existing clay is not suitable for independent pottery making. If we insist on using it, we need to synthesize improved clay, but the necessary purification equipment and high-temperature smelting furnace cannot be built at present."
Chen Hao looked at the picture, remained silent for a few seconds, and then suddenly laughed: "So we've been busy for three days just to prove that a piece of mud isn't good enough?"
"To be precise, it means that the possibility of using local topsoil as the main material has been ruled out."
"You can really say that so calmly." He picked up a pen, drew a big X on the paper, and crossed out "Dongpo collecting soil". "Alright, since there's no rice at home, we'll just have to go out and look for some."
"You propose expanding the exploration area?"
“Otherwise what? We can’t expect this land to suddenly evolve into high-quality porcelain clay, can we?” He stood up and dusted off his pants. “If the East Slope won’t work, let’s go to the foot of the West Mountain. It’s near the rock strata there, and maybe there’s a layer of weathered clay there. There’s also the North Valley Stream, where the constant flow of water should make the clay finer.”
Nana pulled up a topographic map and projected it on the wall: "The west side of the farm is a basalt hill with a thin weathered layer; the North Valley is the end of an alluvial fan, and the sediments are mainly silt with an uncertain clay content."
"We only go to check if we're unsure." Chen Hao opened his toolbox and started stuffing sampling bottles, shovels, and labels into his canvas bag. "Anyway, the waterwheel is running fine now, and nobody's watching us or making us guard the base."
"You mean to abandon improvements and directly search for new materials?"
“It’s not about giving up, it’s about changing our approach.” He slung his bag over his shoulder. “We’ve tried adding sand, ash, and bone scraps here three times, and it’s all been a waste. That means the problem isn’t with our skills, it’s with the raw materials themselves. Instead of getting stuck in this mess, we should find some good soil and start over.”
Nana glanced at him, and the terminal screen refreshed, displaying a new task module: "Geological sampling plan initiated. Target areas: colluvial zone at the foot of Xishan Mountain, terraces along the Beigu Creek, and the edge of the Nanlin Depression swamp. Prioritize testing plasticity, particle composition, and sintering performance."
"Nanlin is going too?" Chen Hao raised an eyebrow. "That place is flooded during the rainy season and bubbling during the dry season. You can sink up to your thighs if you step in."
"Because of the special environment, it is possible to accumulate sedimentary clay rich in organic matter."
"Are you trying to make me a slippery eel?"
"I'm just providing the optimal sampling path."
Chen Hao grinned: "Alright, we'll set off first thing tomorrow morning. First West Mountain, then North Valley, and finally let's see if you can make me swim and collect soil in the South Forest Swamp."
He rolled up the map, casually tucked it into his belt, and picked up the waste bin to empty it.
A pile of broken pottery shards clattered into the recycling bin, one of which had a sharp edge that grazed his palm, leaving a shallow mark.
He shook his hand, not paying any attention.
As darkness fell outside, the waterwheel continued to turn, its creaking sound echoing through the mill's conveyor belt, as if it were yawning on someone's behalf.
On the workbench, three labels lay quietly: t-01, t-02, and t-03, all marked "Unqualified".
Nana is entering the last set of data, and the cursor is hovering over the "Suggested Next Steps" column.
She typed a few words: "[Initiate field clay resource exploration]".
Chen Hao stood at the door, holding an old entrenching tool in his hand. The blade was a bit kinked, but it was still usable.
"Tell me, if we really find good soil, what's the first thing we'll do when we get back?"
"Re-form the billet and verify its stability."
“Too boring.” He shook his head. “I want to make a big one, the kind that can hold twenty kilograms of rice, and then have the words engraved on it: ‘This product is supervised by Chen Hao. We are not responsible for any cracks.’”
Nana looked up at him.
What do you think?
She closed the terminal, her voice flat: "I think you should first learn how to prevent the clay pot from cracking on its own."
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