The sulfur stung before the heat did.
It hit Lin Ke’s sinuses like crushed glass and rotten eggs. It burned down the lining of his throat until every shallow breath tasted of yellow pyrites. Across the flat stone slab floor of the Seventh Smelting Ward, the air rippled with toxic haze.
A fire laborer two benches down dropped his iron rake. The boy doubled over, vomiting a string of black bile and soot onto the melted rock waste-crusted drainage trough, his ribs heaving like broken bellows.
“Get him up,” a harsh voice barked from the draft door. “Or drag him to the scrap pit. We’re forty pounds short of the dawn quota. The checker’s tally-clerk doesn’t accept corpses as melted rock waste deductions.”
Lin Ke didn’t look up from his brass measuring tongs. He kept his spine straight against the stone ledger bench. Even so, the marrow inside his shins throbbed with a dull, sickening ache.
System status, he ran mentally. That kept his breath shallow and filtered through his soot-stained linen collar.
The numbers were deteriorating. The hardened melted rock waste left by the last owner’s forced practice of the backdoored Iron Marrow Manual was hardening in his bones like cheap high-pressure cement. Every heavy lift, every sudden jolt, sent hairline stress fractures shooting through his outward shafts.
And now, Zhao Wuji’s economic blockade was tightening the noose around the ward’s neck.
Three days ago, the Grand Fortune Merchant Clan had bought up every cart of Grade-1 spirit coal earmarked for the Seventh Ward. The carts had been rerouted to the First Ward under the guise of an “emergency high-priority supply order” stamped by some bought-off outer elder. In their place, Zhao’s factors had dumped twenty cartloads of discarded “Cold-Melted rock Tailings”—dull, sulfur-choked pyrite waste scum that wouldn’t burn hot enough to melt lead, let alone refine pig iron.
Fire Number Four was choking.
Inside its massive firebrick bell, the waste scum burned at a sluggish, smoldering cherry-red. Instead of producing fluid, melted rock waste-free iron blooms, the crucible was vomiting thick, thick, sticky scum that welded the lower iron grates shut.
Elder Wu DeZheng scurried into the nook, his silk sleeves hiked up to his elbows to avoid the greasy soot. The round, fleshy man was sweating heavily, his face pale beneath the lantern light.
“Lin Ke! Assistant Ward Clerk Lin!” Elder Wu hissed, pressing a damp cloth to his nose. “Where is the dawn batch? The Outer Court Checker office’s courier is already drinking tea at the outer edge post! If we miss the monthly quota of six hundred pounds, my pension review... That’s, the ward’s charter... Will be flagged for gross fault!”
“The fuel grade is sub-standard, Elder Wu,” Lin Ke said evenly, his voice flat and deadpan. He didn’t blink. “Pyrite content exceeds eighteen percent. The firebox heat is sitting at seven hundred and forty degrees. Iron oxide needs at least eleven hundred to achieve clean separation from the gangue.”
“I don’t care about the degrees!” Wu sputtered, waving a trembling finger at the smoldering chimney. “I care about the tally! If Form 12-An isn’t stamped by noon, Inspector Chai will declare this entire work-yard an unproductive debt. They’ll revoke your office exemption, Lin Ke! You’ll be back down in the melted rock waste trenches carrying hundred-pound baskets on those brittle shins of yours!”
Elder Wu’s panic was real. The man was exactly four years and one month away from his full sixty-year sect retirement pay. To Elder Wu, a royal audit or a flagged quota was worse than an invading demonic army.
“Form 12-A needs refined blooms with less than three percent sulfur waste scum,” Lin Ke noted. He set down his measuring tongs with a precise, metal click. “If we tap the fire right now, we’ll pour a brittle porous sponge. The Checker office will fail it on thickness alone.”
“Then do something!” Wu whispered desperately, leaning in until Lin Ke could smell the expensive lavender oil the elder used to mask the stench of the forge. “You fixed the Nine-Fold cooling loop last month! Fix the fire!”
“Step back from the draft chute, Elder,” Lin Ke said. “The pressure slope is about to reverse.”
He stepped up to the edge of the pit. The heat from Crucible Four hit his skin, dry and blistering. But his left palm remained cool. The carbonized scar tissue from his patched Nine-Fold Crimson loop venting the heat excess directly through his Laogong acupoints without blistering the flesh.
He closed his eyes for a split second.
Tianfu, he commanded silently. Branch.
In the quiet, grey space behind his eyes, the roaring workshop vanished. A wireframe model of Crucible Four rotated in mid-air, its heat gradients mapped in shades of dull orange and cold violet.
Lin Ke ran the obvious patch first: forcing pure Yang Qi into the burning chamber to raise the heat by brute force.
The test model flickered. In the mental model, Lin Ke channeled forty percent of his dantian reserve into the lower chimney pipe. The fire roared, the pyrite ignited, and the heat swelling spiked beyond limit.
Crack.
The heat shock shattered the firebrick crown. Molten sulfur and white-hot iron melted rock waste blew out through the check ports in a total backdraft. In the test model, Lin Ke took forty pounds of liquid metal directly to the chest.
Never brute-force a heat bottleneck, Lin Ke scolded himself coldly. That’s how junior engineers bring down the entire cluster. It’s not a lack of heat. It’s an oxygen-starvation loop caused by melted rock waste thick, sticky drag.
He adjusted the settings in the sandbox.
The cold-melted rock waste tailings contained high concentrations of iron sulfides. If he could introduce high-speed, pre-heated air through the lower draft dampers, the sulfur wouldn’t dissolve into the molten metal. It would oxidize rapidly into sulfur dioxide gas and flash off through the exhaust chimney before it could poison the iron melt.
To lower the melting point of the leftover stone-glass melted rock waste, he needed a backup flux. Limestone was blocked by Zhao Wuji. But the floor around the crucible was littered with crushed bone ash from the mess halls and discarded pink rock gravel.
He modeled the airflow. Open the lower tertiary damper thirty degrees, constrict the upper chimney throttle by twenty percent to build backing-up pressure, and inject tightly packed blast pulses at forty-five cycles per minute.
The mental crucible flared. The sulfur ignited with a clean, whistling blue flame. The glassy melted rock waste floated to the surface, separating cleanly from the dense, liquid iron puddle below.
Lin Ke cut the branch.
His eyes snapped open in meatspace. Embers were still drifting through the greasy air. Elder Wu was still wringing his hands. Less than four seconds had elapsed.
Lin Ke reached into his sleeve, drew his iron metal pen. Then he pricked the calloused pad of his left thumb. A sharp needle of pain grounded him instantly. A tiny bead of dark red blood welled against the metal tip.
“Branch checked: main,” he muttered under his breath.
“What did you say?” Elder Wu squeaked.
“Meng Shan,” Lin Ke called out across the noisy floor.
From behind the cooling troughs, a mountain of a man rose to his feet. Meng Shan’s broad shoulders were bare, crisscrossed with pale burn scars, his skin tinted slate-grey from years of quarry labor. His breathing was heavy, but deep and rhythmic. The distributed earth channels Lin Ke had refactored for him humming steadily beneath the skin.
“Brother Lin,” Meng Shan rumbled, picking up a twelve-foot ashwood crowbar as if it were a twig.
“Take the lower damper lever,” Lin Ke commanded, his voice slicing through the clatter of hammers and choking smoke. “Don’t open it fully. Forty-five degrees only. When I signal, pump the bellows at exactly forty-five strokes per minute. Not forty, not fifty. Forty-five.”
“Understood,” Meng Shan said. He didn’t ask why. A man whose spirit veins had been saved from explosive backfire trusted the engineer without pause.
“You,” Lin Ke pointed to two scared fire apprentices shivering near the coal bin. “Grab three shovels of bone ash from the refuse pit and half a sack of crushed pink rock gravel from the stonework pile. Dump it into the top hopper on my mark.”
“B-bone ash?” one apprentice stammered. “Clerk Lin, that’s refuse! The smelting manual says—”
“The manual was written by an administrator who never held a shovel,” Lin Ke cut him off, his voice flat as an iron slab. “Move. Now.”
The boys scrambled.
Lin Ke stepped up to the fire mouth. He seized the iron draft lever with his right hand. The metal was scalding, blistering the palm through his linen wrap, but his grip didn’t waiver. He calculated the draft speed, eyes tracking the color of the exhaust smoke curling from the chimney.
“Meng Shan—stroke one! Inject!”
Meng Shan hauled back on the massive dual-piston leather bellows. The wooden beam groaned under high-pressure tension. A focused gust of air roared into the bottom of Crucible Four.
“Hopper in!” Lin Ke yelled.
The apprentices dumped the bone ash and crushed pink rock into the charging bell.
For a heartbeat, the fire choked. The cherry-red glow darkened to a dull, bruised purple. Elder Wu let out a high-pitched whimper, clapping his hands over his ears and preparing for the blast.
Then the chemistry took hold.
The calcined bone ash reacted with the pink rock. It dropped the eutectic melting point of the quartz dust melted rock waste by nearly two hundred degrees. The sulfur met the forced draft and flashed into blue fire with a sharp, bone-shaking whoosh.
A column of pale yellow sulfur dioxide roared up the exhaust chimney, venting safely into the high mountain draft above the roofline.
Inside the watching slit, the sluggish sludge melted. It turned from muddy paste into a silky, blazing bright liquid. The green, glassy melted rock waste floated instantly to the surface, bubbling cleanly like boiling broth.
“Meng Shan! Steady at forty-five!” Lin Ke shouted, his voice hoarse from the dry heat. “Keep the intake smooth-flowing! Don’t let rough churning stall the flame front!”
“Holding forty-five!” Meng Shan bellowed, his back muscles bunching like knotted cables as he drove the bellows with clean, steady care.
Lin Ke grabbed an eight-foot tapping rod. He drove the chisel point directly into the clay tap-hole at the crucible’s base.
With three sharp hammer strikes, the plug gave way.
A blinding stream of liquid white-gold iron cascaded out into the sand trough. It flowed with zero drag, smooth and heavy. It glowed with an internal, blasting heat that pushed the choking sulfur smoke back from the floor. Behind it, through the upper skim-gate, the green melted rock waste poured into a separate cooling pit. It hissed as it chilled into brittle, harmless glass.
Elder Wu lowered his sleeves, blinking through tears of grease. His jaw fell open.
“The... The flow,” Wu stammered, stumbling toward the trough. “It’s not foaming. There are no black fissures!”
“Ninety-four percent purity,” Lin Ke said. He leaned on the tapping rod as sweat poured down his neck, soaking his clerk’s collar. “Grade-2 refined iron bloom. About eighty pounds in this tap alone. We’ll clear the quota with sixty pounds to spare.”
Elder Wu let out a ragged breath that sounded like a deflating bladder. He whipped out his official seal and slammed it down onto the damp parchment of Form 12-A, smearing red stone paste across the wood bench.
“Signed! Stamped! Approved!” Wu laughed hysterically, clutching the scroll to his chest. “Let Inspector Chai come! Let the Grand Fortune Clan choke on their coal! Assistant Clerk Lin... You’re a lifesaver. An office pillar!”
Lin Ke didn’t smile. He watched the molten metal fill the sand molds, his internal clock already calculating the cooling rate and crystal-clear contraction.
“Form 12-An only covers this shift, Elder,” Lin Ke noted quietly. “Zhao Wuji still holds the coal supply. Tomorrow we have sixty more baskets of pyrite tailings arriving at the gate.”
“Tomorrow is tomorrow!” Wu barked happily, backing toward the exit to catch the courier. “Keep the boys working! I must file this before the seal dries!”
Wu vanished into the hall.
Lin Ke exhaled, the tension draining from his shoulders. He reached down with a pair of long iron tongs to lift the first solidifying iron bloom from the sand bed to inspect its surface texture.
He took the weight with his left arm.
Crack.
It wasn’t a sound in the room. It was a sharp, brittle shaking sent through his own bone tissue, resonating directly into his hearing canal.
A white-hot needle of pain flared in the middle of his left radius.
Lin Ke dropped the tongs. The iron bloom hit the sand with a heavy thud. He caught his left forearm with his right hand. His fingers pressed into the flesh just below the elbow.
Beneath the skin, the bone was burning with an unnatural, dry heat. A hairline stress fracture had just opened along the outward shaft, splitting through the hardened, poisoned marrow.
Lin Ke gritted his teeth, his vision swimming with grey static.
The melted rock waste in the fire was fixed. But the melted rock waste in his own skeleton was running out of time.