Igniting the Crucible
I bought up wrought iron for steel production to prepare the Crucible Steel Furnace for its first run. It cost about eight Great Tong coins per kg, and with fifty ingots at roughly 2kg each, it set me back fifty silver coins. The wrought iron came from a mining village three or four days' ride away, the one my father had granted to my Eldest Brother as a fief. From what I'd learned, their annual output was 4-5 tons—around 500kg a month—so I'd snapped up about 20% of their monthly production in one shot. Not a trivial amount, but when I thought about the profits if it worked, it was a solid investment.
The issue was the shape of those ingots. Wrought iron bars were sold long and slender, too unwieldy to drop straight into a crucible. For maximum efficiency, they needed to be chopped into pellets, but my workshop had no gear capable of slicing wrought iron. In the end, I commissioned the forge to break them down.
"You want all of these cut up?" The blacksmith gaped at the fifty ingots, clucking his tongue in disbelief.
The job of turning them into fingernail-sized pellets was straightforward enough, but the sheer volume was the problem. They charged me 10% of the iron's value in labor—five silver coins just for that. It stung, but there was no helping it right now. To avoid paying out for this again, my first steel product would be chopper blades for cutting wrought iron.
While I was at the forge, I picked up a long pair of tongs and a scale. The tongs were for pulling crucibles from the still-hot furnace; the scale, for measuring charcoal powder.
Back at the workshop, I got serious about measuring. I weighed a crucible loaded with the right amount of wrought iron pellets, then commissioned the forge to cast lead weights matching that heft. Lead was easy to work, so adding one silver coin on top of material costs covered the labor nicely.
Using that master weight as a base, I had them make 1/10th versions, then 1/10th of those, and so on—chaining down the scales. I prepped at least ten of each size. Precise measurement was the heart of crucible steelmaking. Carbon steel's properties changed drastically with carbon content: low-carbon at 0.05-0.25%, medium at 0.30-0.60%, spring steel at 0.55-0.70%, and my target high-carbon steel at 0.70-1.00%.
Keep the crucible at high heat, and the charcoal powder inside burns to produce carbon monoxide. That gas carburizes the molten iron's surface, then convection spreads the carbon evenly throughout. In theory. Reality didn't play so nice. Dump in charcoal matching your target carbon ratio, and you'd fail every time. Not all the carbon absorbs into the iron—some bonds with oxygen inside the crucible to form CO2 and vents off; some gets trapped in impurities like slag.
So you needed about five times the theoretical amount of charcoal. And even "five times" wasn't absolute. Variables like wrought iron quality, charcoal type, heat time, and temperature made it a crapshoot. Trial and error was the only way to build data.
For this first batch, I prepped eight crucibles, each with slightly different charcoal ratios for comparison. I marked lids and bodies with identifiers to track which was which. Data on the optimal ratio for perfect steel—that was the goal.
I loaded the pellets and measured charcoal into each crucible, sealed the lids, and caulked every gap with fireclay. No air leaks allowed, or iron quality went to hell. Perfect sealing was crucible steel's soul.
Stacking crucibles in the furnace followed pottery kiln principles: firebricks and tiles. I piled the eight sealed ones in two layers of four, smack in the chamber's center where heat circulated best. I packed finger-joint-sized charcoal chunks around them—about 30kg, burying the crucibles completely.
The Crucible Steel Furnace differed from a pottery kiln in heating. Pottery kilns use wood smoke grazing the ware; this one relied on charcoal's radiant heat directly on the crucibles. Unlike logs, charcoal radiated evenly, heating surroundings uniformly. In a big furnace, that meant hot spots, but my small chamber let it envelop everything. Buried crucibles hit peak heat fast—that's why firing took just 3-4 hours, not days.
Prep done. I lit the charcoal pile, then sealed the chamber entrance with firebrick lid and clay. Bellows next—gentle at first.
Fwoooosh.
Weak puffs until flames spread through the whole bed. Smoke thinned, fire stabilized—time for full bellows.
"Clay, this is where it starts. No breaks."
"Yes, sir!"
Clay stomped the foot bellows pedal. Shhhk, shhhk. Steady wind filled the workshop. The chamber's heat climbed slow but sure.
I cracked a pre-made peep hole by the chimney to check without disturbing flow. Blazing heat slapped my face. Squinting in: flames shifted from red to orange. Heating speed crushed pottery kilns.
Soon, orange glowed to eye-searing yellow—over 1,300°C. In the inferno, buried crucibles glowed red, outlines faint but visible. All good. Plug the hole, circle the furnace for smoke leaks.
"Young master... it's tough..."
About an hour in, Clay's breaths ragged. Even her stamina had limits against relentless high heat.
"Switch. My turn."
I shoved her aside and took the pedal. Damn, the heat was brutal. Needed a wooden shield up front. Shhhk, shhhk.
3-4 hours total. I soloed the rest. No visitors all day. No eyes on us—fine by me. Time flew chatting with Clay.
Ding—! Ding—! Ding—! Ding—!
The bell tolled. Bellows done. Tidied up, prepped to leave. Slow cool overnight—no rushing, or crucibles crack and steel structure destabilizes.
Even leaving, the furnace radiated fierce heat. Results itched at me, but full cool meant a full day.
"Good work, Clay. Head home."
"Yes, sir!"
Next morning, Clay waited at the workshop.
"Young master, furnace is still warm."
She touched the wall.
"Let's open it."
Carefully dismantled the entrance seal. Lingering heat, but not killer-hot. Long tongs fished crucibles from ashes one by one. No delicacy needed—they weren't fragile pottery.
Eight crucibles, intact. No cracks, no chips.
Set one on the bench. Hammer up. Tense moment.
Crack!
Smashed the fireclay lid. Silvery-gray metal lump gleamed: an ingot, crucible-shaped and rounded on the bottom.
Too early for victory laps. Melted and set, sure—but real steel? Test time.
Tongs gripped it. Smooth surface, wrought iron's roughness gone, glassy sheen instead. Perfect melt.
Hardness next. File scraped the face.
Screeech.
Shallow scratch, shrill cry. Wrought iron would've gouged deep. Definitely harder.
"Success..."
Grin crept up unbidden.
Opened the rest. One failed—cracked seal let it oxidize into spongy, hole-riddled mess like bloomery sponge iron, worse than wrought thanks to decarburization. Chunk it for next melt.
The rest: seven perfect ingots.
Now, haul to the forge, hammer-test each. Which ratio gave best springiness? Hardest? Data would nail future charcoal loads for reliable steel.
I tracked ratios meticulously.
First: chopper blades. Leftovers into high-carbon tools—files, punches, rasps. Then low- and medium-carbon for my armor and weapons. No village forge for that; pro smiths only. Full plate needed custom work anyway—bring ingots then. Perfect.