The red clay bricks from the common pottery kilns didn’t melt gracefully. They slumped into puddles of bubbling, glassy melted rock waste like burnt sugar.
Master Borin Bronze-Lung pulled a test sample from the small muffle fire with long wrought-iron tongs. He dropped the smoking lump onto the packed earth floor of the foundry terrace.
The brick had twisted into an ugly, bubbled blob of dark red turning to glass. Its sharp corners had rounded off fully. A hairline fracture ran through its core like a split bone.
“Twelve hundred degrees,” Borin said, spitting into the dust.
“Not even hot enough to sweat the copper off a penny. The common field clay turns to grease. If we build a forty-foot blast fire out of this muck, Lord Giles, the stack will melt into its own hearth before we tap the first ladle of pig iron.”
Giles Croft crouched beside the ruined brick, prodding the glassy crust with the tip of his folding rule.
“Too much free quartz dust and bitter salt flux,” Giles said.
“Potassium and sodium oxides in the river mud depress the melting point below thirteen hundred Celsius. It’s fine for roofing tiles or chimney pots, but as a heat-proof lining under nonstop blast, it’s a total collapse waiting to happen.”
Duncan Stone-Splitter leaned on his heavy dressing scutch, his sleeves rolled up to his hairy elbows.
“The old masons in Dunwall used soapstone,” Duncan said.
“Or mica-flaky rock hauled from the western gorges. It holds the flame. But it spalls into flakes as soon as a cold gust of air hits the lining.”
“Natural stone has internal cleavage planes,” Giles said, standing up. “When heat creates a heat slope across the block, differential spreading produces severe sideways tearing force along the bedding planes.
The face shears off in sheets. We don’t use quarry stone for a fire lining. We manufacture engineered refractories.”
Lady Millicent Croft walked down the terrace stairs. She was followed by four laborers hauling two-wheeled hand-carts laden with wooden barrels.
“The dwarven wagons from the Under-Pass have delivered the first twenty tons of white earth,” Millicent announced. He tapped the top barrel with her pencil.
“Thorgan Ironvein’s wagon drivers demanded their receipt in full weight. Every barrel contains dense, unwashed kaolin clay from Mount Thurn.”
“Open three barrels,” Giles directed. “And bring up two tons of calcined flint.”
Toby Karr and three apprentices rolled the barrels onto the mixing platform.
The oak heads were knocked off. Then, the barrels revealed a dense, dazzling white powder that smelled of cold stone dust and mountain rain.
Duncan reached into a barrel, letting the white dust sift through his calloused fingers. “Soft as sifted flour. How can dirt that feels like silk hold a flame that melts iron?”
“Alumina content,” Giles said. “High-purity kaolinite is forty percent light metal oxide and forty-six percent quartz dust.
When fired, it doesn’t form low-melting eutectics. But pure kaolin shrinks by fifteen percent during drying and firing. If we mold it wet, every brick will crack across the middle.”
He stepped up to a row of wooden trough-mixers.
“Which is why we use grog,” Giles said.
Duncan blinked. “Grog? The spiced rum Mistress Pippa brews for the boatmen?”
“Flint grog,” Giles said, with a faint, dry twitch of his lips. “Pre-calcined clay and shattered flint, roasted to red heat and crushed to a coarse, angular aggregate.
It’s already fully shrunk. It forms the skeletal framework of the brick, absorbing heat shock and eliminating shrinkage cracking.”
He turned to the apprentices, pointing to the copper measuring boxes.
“Standard heat-proof formula,” Giles commanded.
“Sixty percent dwarven kaolin, thirty percent crushed flint grog sized between ten and thirty mesh, and ten percent plastic river clay to provide green bond strength. Mix it dry first, then temper with just enough water to allow molding under pressure.”
The mixing floor became a whirlwind of white and grey dust.
Duncan Stone-Splitter took charge of the crushing floor. Using heavy iron-shod rammers, his masons crushed roasted flint nodules into gritty, sharp-edged sand that crunched beneath their boots like coarse sugar.
“Every grain sharp as a broken tooth,” Duncan shouted, inspecting a handful against the sunlight. “The grit locks together like dressed cut stone in an arch!”
Beside the troughs, Master Caleb Thorne-Wood had built four wooden brick molds of seasoned maple, lined with sheet brass to ensure smooth release.
Each mold held two standard box-shaped compartments: nine inches long, four and a half inches wide, and two and a half inches deep.
Giles stood over the first mold, his wooden ruler verifying the internal dimensions.
“Nine by four and a half by two and a half,” Giles noted. “The universal stonework ratio.
Two widths plus a joint equals one length. It allows linked Flemish and English bonds without cutting bricks on site.”
Toby Karr packed the stiff, damp clay mixture into the mold. He used an iron tamper to beat the material into the corners with solid, rhythmic strokes.
THWUMP. THWUMP. THWUMP.
With a clean strike of an iron wire, Toby sliced off the surplus clay flush with the maple frame.
He tripped the release lever, and two clean, bone-white bricks slid out onto a sanded drying board.
They were dense, sharp-edged, and remarkably heavy.
Borin Bronze-Lung picked one up, turning it in his thick hands. “Heavy as lead, smooth as cheese, and not a crack in the skin. But can it take the draft?”
“It has to dry slowly first,” Giles said.
“Seventy-two hours in the shade to remove free pore water. If you fire a green brick with moisture in its core, the water turns to steam, expands sixteen hundred times in volume, and blows the brick into flying baked-clay shrapnel.”
Sister Teresa walked past the drying racks, her apron dusted with burning lime powder. She paused, peering at the long rows of white bricks basking on the pine boards.
“They look like holy tablets,” Teresa murmured, touching the smooth edge of a brick with her fingertip.
“White as altar stones, pressed from the dust of the mountains. Will they hold the flame of the righteous?”
“They will hold two thousand eight hundred degrees Fahrenheit,” Giles said. “Which is quite hot enough for iron smelting and entirely neutral on the question of righteousness.”
* * *
Three days later, the first test batch of two thousand bricks was loaded into the circular downdraft test kiln.
Borin Bronze-Lung watched the charcoal fires through the peep-holes, checking the draft with his disappearing-filament fire gauge.
For thirty-six hours, the heat climbed steadily. That turned the inside of the kiln from dull cherry red to bright orange, and finally into a blinding, blazing bright lemon-yellow.
When the kiln was cooled and unsealed, Giles and Duncan stood at the doorway.
The bricks had transformed.
The dull, chalky white clay was gone. In its place sat rows of rock-hard, pale cream-colored heat-proof firebricks. It rang like fine china as Duncan tapped them with an iron nail.
PING. PING. PING.
“Not a crack,” Duncan whispered, his eyes wide. “Two thousand bricks, and not a single check or blister on the edges.”
“The grog held the dimensions,” Giles said, measuring a sample with his measuring tongs. “Shrinkage was under one point two percent. Crushing strength should exceed four thousand pounds of pressure.”
Borin pulled a fresh firebrick from the stack. Then he held it up to the autumn sky, a broad, fierce grin splitting his beard.
“We have the lining!” Borin roared. “We have the guts for the Great Stack! Let the Black Fen bring its worst frost. We have stone that eats fire!”
Before the cheer could spread across the terrace, a sharp whistle cut through the river breeze from the northern wharves.
Captain Kenneth Drake came jogging along the canal path, his hand resting on his sword handle, his face grim.
“My lord,” Kenneth said, catching his breath. “We have visitors at the lower basin.”
Giles looked down toward the river docks.
Gliding slowly against the current was a heavy, double-banked river galley, its hull painted midnight black and trimmed in cold silver foil.
At its masthead fluttered a long, pointed pennant bearing the radiant sun-wheel and seven-ring chain of the Holy Synod.
Armored men-at-arms in polished steel breastplates and white surcoats lined the boat sides. Their poleaxes shone in the midday glare.
On the raised aft-deck stood a tall, gaunt figure draped in a black glass-colored woolen mantle. An iron censered aspergillum was smoking at his belt.
“Judge Malric Ostrander,” Kenneth said under his breath.
“The Grand Judge’s chief heresy-hound for the Northern Marches. He burned forty heretics in Highmarch two winters ago for preaching that the earth moves around the sun.”
Giles adjusted his glasses, looking from the smoking black galley to the stack of newly fired heat-proof bricks.
“Did he bring a bill of lading?” Giles asked mildly.
Kenneth blinked. “A bill of lading? My lord, he’s an Inquisitor of the Holy Synod. He brings fire and rope.”
“Then he’s in rule-break of town port regulations,” Giles said, closing his notebook. “Unscheduled vessels carrying combustible censers are not allowed within two hundred yards of our drying racks.
Toby, fetch the harbor city law ledger.” Duncan Stone-Splitter stepped to the edge of the terrace, squinting down at the black galley. “Judges don’t care about harbor ordinances, Lord Giles. When they smell smoke that didn’t come from a church candle, they come with chains and branding irons.”
“Then they will learn how an efficient municipality handles unregulated starting sources,” Giles said. He tapped his wooden ruler against his palm.
“Teresa, take two squads with burning lime powder hoses down to the landing quay. If the Judge steps off the gangway without a health clearance, enforce a full forty-day quarantine for communicable marsh fever.”
Sister Teresa’s eyes flared with zealous delight. “The quarantine of the righteous! No unclean foot shall touch our lime-washed stone!”
Kenneth Drake rested his pacing rod on the gravel, a dry smirk touching his lips. “You’re going to arrest the Grand Judge’s chief prosecutor with a bucket of wet lime plaster?”
“I’m not arresting him,” Giles replied, heading down the wooden terrace steps.
“I’m subjecting him to standard sanitary intake protocols,” Giles replied, heading down the wooden terrace steps. “If he wishes to inspect our kilns, he will do so in a sterilized linen gown like everyone else.”
Behind them on the foundry terrace, Master Borin laughed until his copper-braided beard shook.
“A linen gown for the Heresy-Hound!” Borin bellowed, slapping his thigh. “By the deep roots, I’d pay forty silver sovereigns just to watch the holy father scrub his boots in Teresa’s vinegar tub!”
Toby Karr was already sprinting down the gravel ramp. He grabbed a thick bundle of town registry scrolls under each arm.
The river wind blew cold off the water. It snapped the black silk pennants of the Synod’s galley as its oars backed water against the stone quay.
The stage was set for a crash between holy dogma and local zoning bylaws.