Substitute Flux Triumph and the Slave Market
The day after the substitute flux test, I dove into refurbishing the Crucible Steel Furnace with Clay.
When we'd first designed and built the furnace, one issue we hadn't anticipated cropped up. The inlet was at the top, making it a nightmare to scoop out the ash buildup inside or clean it with water. To repack the chamber with fresh mortar if something went wrong and recoat it with white refractory, we had to empty it completely first. But squeezing my body through that narrow opening to shovel out the ash was far more grueling than I'd imagined. What should've taken minutes in a different furnace design would drag on for hours here, grunting and struggling.
I boldly decided to skip the deep clean. Better to spend that time elsewhere—rebuilding from scratch if it failed would save time in the long run. It could handle about twenty runs without maintenance anyway, so next time I'd redesign with this flaw in mind. We settled for roughly scraping out the ash from the chamber.
I immediately commissioned the carpenter to build a wheeled wooden panel screen to place between the bellows and the furnace. At peak temperature, the radiant heat pouring out was brutal for anyone to endure. Wood's low thermal conductivity meant a simple barrier like this would cut the perceived heat dramatically for the workers. From now on, Clay or I could pump the bellows in much more comfortable conditions.
With the work environment upgraded, it was time to cut losses in the process itself. We needed a fundamental fix for crucibles breaking. Each furnace run guzzled 30kg of charcoal. If one crucible shattered mid-heat, we'd waste an eighth of the fuel cost plus the crucible fabrication expense—straight down the drain.
Since we were hand-sealing crucibles with refractory clay, cracks or breaks during heating were always a risk. We needed a real solution.
Truth be told, I already knew one. Adding borax—a flux—along with charcoal powder inside the crucible would solve it. In my past life, borax was widely used in carbon steel forging, welding, and soldering to strip away oxide layers. Toss it in here, and it melts before the iron, coating the molten metal to block oxidation. It reacts with oxygen in place of the metal, letting us slash the charcoal powder from five times the theoretical amount down to 1.5 times. Plus, it absorbs impurities like slag, lowers their melting point to liquefy them, making separation from the cooled steel a breeze later.
But flawless borax had one fatal flaw: where the hell do I get it?
Asking around merchants in this world turned up zero hits—not a soul knew of anything like borax ore. It comes from dried lake beds in arid regions with ancient volcanic activity, a freakishly unique terrain no one nearby could've missed. Even on old Earth, it was rare, limited to spots like specific salt lakes in Turkey or deep cave hot springs in volcanic zones.
Hunting across the continent for volcanic areas just to tweak crucible failure rates? Bad math.
I needed a substitute.
Borax won't work... glass powder?
It performed a bit worse than borax but could mimic the effect. Problem was, glass was scarce and pricey here too. A small cup of murky green forest glass cost a silver coin. Clear glass? Priceless.
Grinding expensive glass for crucible steel? That'd cost more than it saved.
Making my own glass? ...
"Hm?"
I ran through glassmaking in my head. For murky forest glass as flux, it was dead simple: mix sand with wood ash. Sourcing silica sand would've been a hassle, but I already had mountains of fine sand from soil sorting and sedimentation. Wood ash poured out every furnace run, so materials were basically free.
Glass powder melts at borax-like temps, but synthesizing from raw sand hits over 1200°C initially. Add salt, though, and it drops to around 1000°C.
Pack the crucible with wrought iron scraps and charcoal powder, then top with a mix of sand, ash, and salt for forest glass—20-30g for this size. The glass forms and melts before the iron, acting as an oxide barrier just like borax.
Liquid glass is highly acidic, though, risking corrosion through the crucible walls. Low viscosity might also let it bubble and break the seal when gases escape the melt, like boiling water.
Easy fix: mix in kaolin clay powder to neutralize acidity and boost viscosity.
This could work.
The ratios clicked in my mind: sand, ash, salt, kaolin at about 1:1.5:1:0.5.
All materials were on hand in the workshop except salt—grab a sack from the market. 25-30kg per bag ran 7-9 silvers, enough for 2000 crucibles. Way cheaper than buying glass powder.
And unlike borax, this had an unexpected bonus: the glass byproduct, slag-loaded, could be collected, remelted, and shaped into murky forest glass products. Lower quality—impurities make it harden fast, hard to work, full of bubbles and opaque—but glass still fetched premium prices.
Producing steel and glass as byproduct? Double win.
I even knew quality upgrades: manganese for decolorizing, nitre for bubble removal and clarity. Manganese ore often came with iron, so easy from an iron-mining village. Nitre? Scrape stable floor dirt and refine—not much needed.
No immediate glassmaking plans, but no reason not to prep.
After that, I bought salt from the market and kicked off crucible steel production with the substitute flux. Results were a resounding success.
The steel ingots from the crucibles shed glass cleanly under hammer blows, leaving perfect bars. Even with seal cracks, the glass discolored blackish-red, but the steel came out fine.
Thus, crucible steel production was fully established.
A month passed. Clay and I ran the furnace nonstop.
Carbon steel ingots—oiled for protection—stacked neatly in one warehouse corner: 40 low-carbon, 30 medium-carbon, 10 high-carbon. Total 80. Top-grade by this world's standards, enough for luxury goods.
Beside them, scraped-up broken glass chunks sat sorted on shelves. Remelt those later for glassware, and it'd make nice pocket money.
Gazing contentedly at the steel pile, I reviewed next steps.
Take it to Wainwright Count's Castle. Not just to sell, but to commission gear tailored for me.
Few here could work steel properly. I'd taught the village blacksmith basics, but he wasn't crafting balanced weapons considering weight, center of gravity, range of motion—definitely no expert armorer.
For custom-fit gear, I needed a skilled smith in the city.
Naturally, that sparked thoughts on manpower.
Time to hire more hands?
Clay maxed out at crucible steel production. Her workshop hours were manageable, but add mansion duties as a servant, and it was too much for one halfling orphan.
Hiring for cash was easy. Tech leakage? The real issue.
Crucible steel was light-years beyond local tech—a golden goose. Medieval-replicable too: low skill barrier, anyone knowing the method could copy it.
At minimum, Clay-level contract scrolls silenced leaks. She'd accepted easily as a rootless orphan with no future. But foisting binding magic contracts on randos? Tough sell.
Scrolls weren't cheap either. Hires had lives, families—I couldn't drag them forever.
They work years, quit: scroll blocks leaks, but training wasted. New hire? Retrain from zero.
Big corp systems handle turnover with handover protocols. Here? Cottage industry—no chance.
Lucky if one sticks long-term, but no guarantees. Constant recruiting, expensive scrolls, reteaching? Costly in time and silver.
Plus, I'd leave the county at adulthood. How many would uproot with me, kin and friends nearby?
Regular laborers were out.
Alternative? One only: buy slaves.
Here, slavery stemmed from four sources: war captives, debt slaves, criminals, fallen noble houses.
Slave traders to this border? Mostly debt-bankrupt self-sellers or caught bandits.
Auctions ran periodically at the count's castle. With cash piled up, I'd snag suitable ones on the trip.