The copper coins he got by trading cured meat and stir-fried dishes acted like a catalyst, pushing Du Heng’s “Two-Year Revival Plan” into the second stage ahead of schedule. By the time the wind of the 7th year of Zhenguan blew across the field ridges of Dujiawa, he was no longer satisfied with merely solving the problem of food and clothing and had started to plan something grander… how to let more people see his gewu philosophy, especially the influential nobles in Chang’an City who could change the overall situation.
“Even good wine fears a deep alley.” Du Heng stood in the courtyard, his gaze resting on the mottled outer wall of the earthen house, his fingers unconsciously rubbing the rough surface. “I need to make a signboard so that people passing by can remember it at a glance.”
But the money in his pocket was only just enough to buy some ingredients and tools; how could he have any spare to hire a painter, let alone buy expensive pigments? Du Heng squatted at the base of the wall, stared at the dirt on the ground and pondered for a long time, then suddenly his eyes lit up… wasn’t there ready-made “pigments” in the mountains? When he had gone into the mountains before, he had seen a kind of red earth that turned into a beautiful ochre when it met water, and there was chalkstone that, once ground, became a natural white base; as for green, he could grind copper-bearing minerals from the mountains into powder and mix them with water; black was even simpler, he just needed to burn some pine branches and collect the soot; as for red, he could pound some wild berries, and the juice he squeezed out was bright red, just right as a rouge shade.
“People in ancient times already used natural mineral pigments like this to paint; I am just picking up their ready-made wisdom.” Du Heng clapped the dust off his hands and that very day shouldered a sack and went into the mountains.
Early the next morning, the villagers of Dujiawa saw Du Heng carrying several millstone-sized rocks and busily working on the outside of his courtyard wall. He first cleaned the wall, wiped off the surface dust with a damp rag, then mixed the red earth, chalk, and green clay with water into pastes and put them into clay jars, and separately placed the pine soot and wild berry juice into small bowls; the five-colored “pigments” were lined up neatly at the base of the wall, making him look exactly like a “country painter” about to start work.
Du Heng planned to paint a “Pastoral Gewu Diagram” on the courtyard wall. He had no prepared draft and relied entirely on the memories and images in his mind. He first used a charcoal stick to lightly sketch the outlines on the wall: the distant Zhongnan Mountain was wrapped in cloud and mist, looming and indistinct; the nearby field ridges were laid out in neat rows like a chessboard; the hens in the chicken coop were stretching their necks to crow, and the piglets beside the pigpen were rooting for food, forming a bustling pastoral scene. Yet this painting was also different from ordinary pastoral scenes…
He drew a set of pulley water-lifting device in the fields, with the rope looped around the pulleys and the bucket hanging down as if it were about to be filled with water in the next second; beside the stove he deliberately drew the trail of steam rising from the mouth of the clay jar, wisps of white smoke curling upward, and even added a small arrow beside it labeled “Water Vaporization”; under the drying rack he wrote in small characters, “3 key elements of fermentation: temperature, humidity, time,” and drew a little icon next to each element; he even drew a cyclical flow beside the chicken coop with arrows showing “chicken manure → compost → fertilize the fields,” like a simple ecological diagram.
Most astonishing of all, Du Heng also used perspective and light-and-shadow techniques in the painting. The distant mountain ranges were colored lightly with blurred lines so they appeared especially far away; the nearby houses had three-dimensional shading, with the bases of the walls drawn dark and the eaves drawn light, so at a glance it looked as if a real house were standing there; even the cured meat hanging from the drying rack had one side bright and one side dark because of the “sunlight” drawn on it, so that it seemed as if one could feel the texture of the cured meat. In an era like Great Tang, when freehand landscape painting prevailed, this was like a sudden clap of thunder that left everyone stunned.
At first the villagers only watched from a distance, but the more they looked, the more curious they became, and they all gathered around. Auntie Li pointed at the pulley device on the wall, widened her eyes, and asked, “Xiao Heng, what did you draw here? Why does it look so real I almost want to reach out and pull that rope?”
Uncle Wang stared at the steam beside the stove, smacked his lips, and said, “The smoke coming out of this stove somehow feels as if it’s really hot. Your painting is too magical!”
A few half-grown children ran around the wall, pointing at the chickens in the painting and shouting, “Look, look! The chickens are moving! One just jumped onto the rack!” In fact, the chickens had not moved at all; it was just that Du Heng had used dynamic lines and shadows to create the feeling of “the chicken just leaping onto the rack,” which misled the children into thinking they had seen it move.
The news seemed to grow wings and quickly spread to the nearby villages. In just 3 days, commoners from all around brought along both the elderly and the young to Dujiawa to see “the Du family sacred wall”. Some people thought the figures on the wall were immortals and even burned incense and knelt at the base of the wall, muttering, “Painting connects to the divine and blesses us with favorable weather and timely rain.” The village tutor also brought his students, pointed at the pulleys and steam tank in the painting, and said to them, “Look, there are principles of gewu hidden in this painting, and they explain things more clearly than the books!”
Faced with everyone’s amazement, Du Heng only smiled and waved his hand. “There’s nothing miraculous about it; I merely drew on the wall what I usually see and think about.” He also deliberately left “flaws” in the painting… for example, writing “save 3 times the effort” beside the pulley system and annotating “Water turns into vapor, and its force can push stones” under the steam tank. These words aroused curiosity but did not fully explain the principles, and he waited for someone to come and ask.
This was precisely Du Heng’s little strategy: first use visual impact to shock everyone, then use the practical knowledge in the painting to solidify their trust, and slowly sow the seeds of “gewu.” (“Investigation of things” is the starting point of the Confucian “Eight Items”)
At dawn on the 7th day, an inconspicuous green-canopied carriage quietly stopped at the entrance to Dujiawa. The curtain lifted slightly, and a middle-aged man in a plain brocade robe stepped down, followed by two guards with long sabers at their waists. The man’s bearing was steady and his gaze deep; he stood with his hands clasped behind his back in front of the mural for a long time without speaking, letting his eyes sweep over every detail on the wall again and again.
“This youth can actually use an earthen wall as paper and minerals as ink to paint the scene of ‘gezhi.’” The man sighed softly and lightly tapped the steam tank on the wall with his finger. “What is even more rare is that he does not flaunt his skill in painting but speaks only of practical things… pulleys that save effort when lifting water, steam that can store power; these are all good things that can benefit the common people.”
The guard beside him leaned closer and quietly reminded him, “Your Majesty, this place is remote and crowded with people, so there may be risks; how about we go back first?”
“It is of no matter.” The man waved his hand, a trace of expectation in his tone. “I came out in plain clothes this time precisely to seek out worthy talents. If this youth truly has ability, he is far more useful than reading a hundred memorials.”
It turned out that this middle-aged man was none other than the current Son of Heaven… Emperor Taizong of Tang Li Shimin. A few days earlier, a Persian Hu merchant from the West Market had specially taken “Du Clan cured meat” to Honglu Temple as an offering, praising it nonstop: “There is a wonder-worker in Great Tang! He can use fire to refine such fragrant meat that the whole of Chang’an can smell it!” At the time Li Shimin had not really believed him and merely assumed the Hu merchant was exaggerating. Unexpectedly, at court that morning, the Minister of Works had memorialized, “There is a youth at the foot of Zhongnan Mountain who paints on walls, and the mechanisms in his paintings seem able to save the people’s labor, leaving the common folk all astounded.”
Putting these two reports together, Li Shimin’s curiosity was piqued, and he promptly decided to go out in disguise and personally take a look at this “remarkable person.”
At that moment, Du Heng was in the plantation in the eastern zone watering soybeans. He wore a coarse hemp short jacket, with his pant legs rolled up to his knees, revealing his sun-darkened shins. His hands were covered in mud as he carefully used a wooden ladle to water each soybean seedling, completely unaware that a noble guest had arrived at the village entrance.
Li Shimin walked slowly along the ridge of the field, looking at the boy’s thin yet straight back and at how focused he was while watering; there was not the slightest hint of servility in his brows, only concern for the crops. He could not help but ask, “Little langjun, was the painting on the wall done by you?”
Hearing the voice, Du Heng stopped what he was doing and turned around. He lifted his eyes and saw that the newcomer had an elegant bearing and eyes sharp as an eagle’s, with guards bearing swords standing behind him, and he instantly understood that this was definitely no ordinary wealthy man. Yet he did not panic; he put down the wooden ladle, wiped his hands on the hem of his clothes, folded his arms and bowed. “It was indeed drawn by this commoner. It is just some crude stuff that will only make you laugh, honored sir.”
“Crude?” Li Shimin pointed with interest at the steam tank in the mural and asked, “Then tell me, what use does this thing have?”
“Honored sir, when water boils it turns into steam, and when steam gathers it produces strength. That strength can be used to turn a millstone, lift water, or cook food, saving ten times the manpower.” Du Heng answered crisply and without the slightest hesitation.
Li Shimin then pointed at the pulleys on the wall. “You say these pulleys really save effort when lifting water?”
“They save at least three times the strength. If you match them with gears, they save even more effort and can also change the direction of force, which makes it very convenient whether for lifting water or moving things.”
A glint flashed instantly through Li Shimin’s eyes… this youth actually understood gears as well? One had to know that most craftsmen of the time only grasped simple mechanical principles; the fact that he could even mention “gears” showed he had done in-depth study of mechanisms.
Feigning nonchalance, Li Shimin went on to ask about farming, water conservancy, manure, and other livelihood issues. Du Heng responded fluently; when he spoke of farming, he not only cited knowledge from Qimin Yaoshu but also did not confine himself to the book, proposing fresh ideas such as “crop rotation can prevent the decline of soil fertility” and “composting can kill insect eggs,” which made Li Shimin nod repeatedly.
“How many books have you read?” Li Shimin could not help asking.
“Honored sir, this commoner has only read half a scroll of Qimin Yaoshu. As for the other knowledge, it all came from watching with my eyes, thinking with my mind, and slowly figuring it out.” Du Heng answered candidly without the least concealment.
Li Shimin could not help bursting into hearty laughter. “What a ‘watching with your eyes and thinking with your mind’! In my view, you are no creature meant to remain in a backwater pond.”
He turned to get into the carriage and leave, but after taking a few steps he stopped again, looked back at Du Heng, and said, “If I were to bestow silk on you to help you paint more walls like this and spread the principles of gewu, would you be willing?”
Du Heng bowed deeply, his tone firm. “What this commoner wants is not silk, but an opportunity… an opportunity to let all under heaven know that the art of gewu can make the people prosperous and the nation strong.”
Li Shimin gazed at the youth before him for a long moment, then slowly nodded. “What fine ambition! I will remember you.” With that, he got into the carriage with his guards, and the carriage soon disappeared along the small road outside the village, leaving only a trail of dust in its wake.