The stone tower rose like a truncated obelisk against the northern bluffs.
For fourteen days, sixty masons and thirty joiners had swarmed over four tiers of spruce work frames. It laid course after linked course of cream-colored heat-proof firebrick.
By late afternoon of the fourteenth day, the structure had reached its full, imposing height of forty feet.
The outer shell was a massive, square pyramid of dressed granite cut stone, tapering gently inward as it climbed toward the throat.
Inside this granite envelope, cushioned by a six-inch insulating layer of crushed diatomaceous earth and dry sand, sat the circular heat-proof shaft.
Giles Croft stood on the timber charging platform thirty feet above the foundry floor, his leather coat dusted with dry lime mortar.
He leaned over the wooden guardrail. He held a plumb-bob suspended on a braided silk cord down into the yawning throat of the fire.
“Bosh angle is seventy-nine point eight degrees,” Giles called down into the echoing brick shaft.
“Well within acceptable clockwork limit. The inward slope will support the dropping burden weight while allowing the softening iron to expand freely into the melting zone.”
Down in the dim, circular crucible at the bottom of the stack, Master Borin Bronze-Lung’s torchlight flickered against the smooth firebrick walls.
“It feels like standing inside the belly of a stone dragon,” Borin’s voice boomed upward, muffled by forty feet of brick.
“Not a single ledge or lip for the ore to snag on! Smooth as a maiden’s wedding kettle!”
Master Caleb Thorne-Wood stood on the upper narrow high walkway, directing the hoisting crew at the central gin-pole.
A heavy block-and-tackle creaked under the strain of a three-hundred-pound wrought-iron hoop, four inches wide and an inch thick, forged in quarters and joined with massive threaded turnbuckles.
“Lower away, lads!” Caleb shouted, waving his leather mittens. “Ease her down over the stonework crown! Don’t let the iron scrape the new mortar!”
The iron hoop slipped down over the narrowed granite stack. He settled into a pre-cut stone rebate twenty feet above the foundation.
Duncan Stone-Splitter and two apprentices right away attacked the turnbuckles with five-foot iron wrenches. He hauled the nuts tight until the threaded rods hummed with tension.
“Hoop number eight secured,” Duncan reported, wiping his brow with his sleeve. “That’s twelve iron belts binding the stone from foundation to throat.
What are you afraid of, Lord Giles? Do you think the rock will run away?”
Lady Millicent Croft walked along the newly erected timber incline that connected the upper charging platform to the bluff terrace.
Her double-entry thick parchment ledger was open against her forearm, her brass nib scratching across the ruled columns with brisk power.
“Twelve wrought-iron tension hoops at three hundred pounds each,” Millicent recited, her glasses catching the autumn glare.
“That’s eighteen hundred pounds of refined bar-iron from our strategic emergency reserves. Plus two thousand square feet of seasoned three-inch spruce planks for this charging ramp.”
She looked over the handrail at the team of draft mules hauling a wooden skip loaded with roasted bog-iron ore up the incline.
“If this fire doesn’t pour fifty tons of usable metal before the first blizzard, Giles,” Millicent continued, “the settlement will be entering the deep winter with empty ore bins, exhausted charcoal reserves, and twelve very expensive iron belts hugging a cold pile of granite.”
“It will pour sixty tons in the first week, Millicent,” Giles replied, checking the cable tension on the inclined railway hoist. “A properly balanced nonstop blast stack doesn’t operate in batches like a bloomery hearth.
Once ignited, the burning zone is self-sustaining. The dropping column of iron ore and limestone flux is continuously preheated by the climbing carbon monoxide gas. We don’t shut it down until the heat-proof lining needs relining in two years.”
Millicent paused, her quill hovering over the thick parchment. “Two years? Without extinguishing the fire?”
“Nonstop operation is eighty percent more fuel-efficient than cyclic batch smelting,” Giles said. “Every time a bloomery cools, you lose the sensible heat stored in twenty tons of stonework. That’s pure heat waste.”
“Hoop stress,” Giles replied, dropping the ladder to the mid-tier scaffold.
“Heat swelling in a blast fire isn’t uniform. The internal heat-proof core expands radially when heated to fourteen hundred Celsius. Meanwhile, the outer granite casing remains relatively cool.”
Duncan tightened another nut with a grunt. “So the core pushes outward?”
“Tremendously,” Giles said.
“Without these wrought-iron tension bands, internal heat pressure would split the stonework shell vertically down all four corners. The fire would burst like an over-high-pressure boiler, dumping twenty tons of molten melted rock waste and liquid iron onto the foundry floor.”
Duncan paused, his hand frozen on his wrench. He looked at the iron band with sudden, deep respect.
“A belt to keep the mountain from bursting its breeches,” Duncan muttered. “I’ll give her another half-turn.”
Down on the ground level, Toby Karr was kneeling before the base of the fire, smoothing a thick layer of black, buttery paste into the joints of the hearth floor.
Beside him sat three iron tubs filled with crushed vein graphite, mixed with boiled linseed oil and fine heat-proof kaolin.
“Is the crucible floor sealed, Toby?” Giles asked, stepping off the bottom rung of the ladder.
“Three coats of graphite paste, Lord Giles,” Toby said, looking up with soot-rimmed eyes. “Tamped down with the wooden beaters until it rings like slate. Borin says liquid iron won’t stick to graphite.”
Sister Teresa of the Pure Cistern walked the length of the raw material stockyard. Her skirts were tucked into her apron.
She carried a long-handled copper ladle and a phial of clear vinegar. She tested the crushed limestone flux stored in the covered timber bunkers.
“Pure white spar-stone from the dwarven Under-Pass,” Teresa announced. She watched the stone dust fizz vigorously in the acid.
“Free of rotten-egg marl and marsh muck. If the breath of the forge is to burn without sin, the stone that cleanses the iron must be white as virgin snow.”
Duncan Stone-Splitter leaned against his sledge, wiping sweat from his red neck. “It’s just chalk, Sister. Good mountain limestone to make the melted rock waste run sweet.”
“Nothing in this yard is ‘just chalk’, Master Duncan,” Teresa countered with stern conviction.
“The limestone binds the black waste scum of the swamp, separating the pure metal from the filth of the earth. It’s an allegory of spiritual purgation made manifest in rock.”
Giles stepped past them, tapping a sample of dried peat coke with his wooden ruler. “It’s basic stoichiometry, Teresa.
White lime-chalk calcines into calcium oxide, which reacts with quartz dust to form liquid calcium metasilicate melted rock waste. If the melted rock waste doesn’t melt at fourteen hundred degrees, the hearth freezes. The holy implications are entirely optional.”
“Liquid iron has high carbon solubility,” Giles explained.
“It will saturate with carbon from the fuel. But it can’t dissolve pure crystal-clear graphite at standard hearth heat levels. The graphite layer protects the hearth firebricks from chemical erosion by the acidic melted rock waste.”
Borin emerged from the bottom clean-out arch, blinking in the bright autumn daylight. His bald head was smudged with black graphite, but his eyes were gleaming.
“The taphole is dressed,” Borin said. He pointed his stubby finger at the base of the front wall.
“Six inches above the floor for the iron notch, and eighteen inches higher on the side for the melted rock waste runner. Both plugged with plastic fireclay.”
He turned, gesturing toward two heavy copper castings bolted through the side walls of the bosh, four feet above the hearth.
They were double-walled, water-cooled copper tuyere nozzles, each six inches in width. They pointed downward into the burning zone at a ten-degree angle.
“The copper snouts are mounted,” Borin said. “Cast from pure red copper, three-quarters of an inch thick. But now comes the question, Lord Giles.”
Giles adjusted his glasses. “Which question?”
Borin pointed at the two wide copper pipes.
“The air,” Borin said, his voice dropping into a solemn, troubled rumble. “I calculated the hearth volume with Toby this morning.
To burn fifteen tons of peat coke and keep twenty tons of bog-iron liquid, this fire needs air. Not a blacksmith’s puff. Not a hearth breeze.”
He looked at Giles, his copper beard bristling with grim doubt.
“It needs fourteen hundred cubic feet of nonstop blast air every minute,” Borin said.
“At four pounds of pressure. If we put sixty laborers on the biggest leather hand-bellows in the province, forty men would drop dead of burst lungs before noon. The fire would freeze into a solid thirty-ton block of dead iron.”
Captain Kenneth Drake walked over from the canal stone retaining wall. He leaned on his ten-foot pacing rod.
“Borin is right, my lord,” Kenneth said. “We don’t have the lungs for this beast.
Even if we took every conscript from the timber gangs and chained them to pump-handles, men tire. Flesh breaks. If the wind stops for twenty minutes, your four-hundred-ton tower becomes a giant tombstone.”
Giles looked from the copper tuyere nozzles down toward the rushing torrent of the drainage canal, barely fifty yards away.
The water diverted by the great drain tube loop was roaring through the newly excavated timber raceway. It dropped eight feet over a timber spillway with thunderous, foaming energy.
A faint, dry smirk touched Giles’s lips.
“Flesh is an atrocious prime mover for nonstop heavy-duty cycles,” Giles said. “Its clockwork smooth speed is under twenty percent, it needs eight hours of daily downtime for defragmentation, and its mood debuffs are unpredictable.”
Kenneth blinked. “Defragmentation?”
“Sleep,” Giles clarified. “We’re not using human lungs to blow this fire, Kenneth.”
He pointed his wooden ruler at the rushing water of the canal race.
“There is forty horsepower of striking force tumbling over that spillway right now, fully unharvested.
Toby, fetch Master Caleb and the timberwrights. We’re going to build a pair of twenty-four-inch cedar back-and-forth piston blowers, driven by an undershot breast-wheel.”
Borin stared at the canal, then at the fire stack.
“A machine that breathes?” Borin whispered.
“A machine that breathes without lungs, without tired arms, and without asking for a beer ration,” Giles said.
Kenneth looked at the foaming chute of the canal, then back at the silent stone stack towering forty feet into the autumn sky. A fierce, hungry grin spread across the ex-sapper’s scarred face.
“A forge that never sleeps,” Kenneth said softly. “The Duke of Highmarch has eighty blacksmiths in his capital, and they couldn’t turn out forty tons of iron in a season.
If this wheel turns the bellows, my lord, we won’t just make nails. We’ll make empires.”
“First we make pigs,” Giles said dryly, turning toward the carpentry shed. “Let’s lay the axle timbers.”