Borrowed Interest
The forge felt considerably more crowded than usual. Gorthruk examining the rough dome sketches with his usual careful scrutiny, Petrov cross-referencing the panel count against realistic production timelines, and Thoth's long neck craned through the doorway, wings folded tight against his sides outside, his head the only part of him that actually fit into the workshop itself.
"Build me a prototype panel," Gorthruk said finally, after a long, considering silence. "One piece, full scale, before I take thirty-six thousand of anything to the council."
Arista nodded, already sketching out the batch calculations, and found herself, almost without thinking, reaching for the exact same reinforced glass formula she'd developed for the submarine's viewport, the one piece of the original design that had survived three hundred meters without a single complaint, long after the cloud material lining had failed catastrophically around it.
Bram, watching her sketch out proportions with the specific, unhesitating confidence of someone who'd done this exact calculation before, tilted his head. "...I just took the glass on the sub for granted, honestly. Since when do you know how to make glass?"
"Three sleepless nights and about twenty-six failed experiments," Arista said, entirely matter-of-fact, not looking up from her notes. "Give or take. I stopped counting properly somewhere around attempt fifteen."
"That's oddly specific for something you're claiming you didn't count."
"I said I stopped counting properly. I still remember roughly how many things exploded." She tapped her notebook, flipping briefly to an earlier, heavily annotated page. "Turns out regular sand-based glass shatters under pressure exactly the way you'd expect. Had to layer it, mineral compound sandwiched between two thin glass sheets, same underlying principle as the Damascus fold on my very first pickaxe: let each layer handle what it's actually good at instead of asking one material to do everything."
"Where'd you even source a mineral compound for something like that?"
"Singing rock, actually. Same stuff I used for the piezoelectric chamber." Arista shrugged, entirely too casual about it. "Back when I was researching quartz for the electric eel setup, I made the connection pretty quickly, same crystalline structure as what Gorthruk's people found deeper in the mountain, just under a different name here. Figured if it behaved anything like real-world quartz, it'd probably add some genuine structural rigidity too, not just the electrical properties. I'm just glad that gamble paid off."
Bram went very still. "...Wait. You mean the glass on the sub could have shattered, at three hundred meters, because you took a gamble?"
"An educated guess."
"You just said gamble."
"An educated gamble," Arista corrected, entirely unbothered. "There's a difference."
Gorthruk's smiths spent the better part of the morning roughing out a hexagonal mold to her specifications, six equal sides meeting at precise one-hundred-and-twenty-degree interior angles, deep enough to hold the full thickness of the layered pour.
"Deeper than you'd think," Arista said, checking the mold's dimensions one final time before the actual casting began. "Glass wants to slump and thin out at the edges as it cools if the mold isn't deep enough to compensate. Learned that one the hard way too."
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Casting a sheet this size took the better part of the afternoon, careful, methodical pours into the finished mold, one layer at a time, cooling slowly enough between each to avoid the stress fractures that had ruined her first two attempts at the viewport's much smaller scale.
"...This held at three hundred meters," she said, half to herself, once the sheet had finally set properly. "The dome's only sitting at a hundred and fifty. If it handled twice the pressure it actually needs to handle, it should hold this application easily."
She framed the glass in a thin but sturdy border, five centimeters of solid adamantium, just enough to anchor the hexagonal spline joints Claire had designed, distributing load evenly across the panel's entire edge without wasting a single gram more of the material than the job actually required.
Bram, watching her work through the adamantium stock with practiced, familiar ease, raised an eyebrow. "...Good thing your shed's stacked."
"Very good thing," Arista agreed, grinning despite the sheer, absurd convenience of it. "Two years of forgotten royalty payments, finally earning their keep."
The finished panel came together within the hour, a clean, hexagonal sheet of pressure-tested glass, locked into its adamantium frame, wedge-cut edges ready to interlock with neighboring panels exactly as Claire's sketch had promised.
Gorthruk examined it for a long time, walking slowly along one edge of the massive prototype, running careful fingers over the adamantium frame and studying the beveled joints where neighboring panels would eventually connect.
"...The city beneath the water does not interest me," he said finally. "I have no particular stake in mermaids, or ruins, or whatever ancient thing you found down there. That is your project, not the Republic's."
"...Fair," Arista said, unbothered. "Wasn't expecting you to care about that part."
"But this-" he tapped the hexagonal frame itself, "-this I care about a great deal."
Petrov glanced up from his production notes. "The frame shape specifically?"
"The Republic's tunnels have collapsed before," Gorthruk said, quiet, matter-of-fact. "Rarely. Infrequently. But it happens, over centuries of mining, when a section's structural support finally gives out under the weight of the mountain above it. We reinforce as best we can, but our current methods rely on individual supports fighting the mountain's weight independently, each one bearing its own share of the load in isolation."
He tapped the adamantium frame again.
"This design does something different. The frame spreads the load across the whole structure instead of asking one support to carry it alone."
Arista sat with that, genuinely surprised by the direction his interest had taken. "...You want to use the hexagonal frames in your own tunnels."
"Connected to one another," Gorthruk said. He tapped one corner, then the next. "Steel beams between the vertices. One frame supports the next. No section carries the mountain alone."
He stepped around the massive prototype, studying the frame from different angles.
"Your glass and joints are your problem. The frame is what interests me. If that geometry can spread the weight of a mountain across several supports instead of one, then it is worth testing."
Thoth, still craned through the doorway, tilted his dish slightly, observing the exchange with quiet, patient interest. "The underlying geometric principle is agnostic to application," he offered. "The dome's spline joints provide additional resistance by locking more tightly under pressure, but they are not themselves the primary load-bearing structure. The frame distributes force through the surrounding geometry. Gorthruk's proposed system would use the same frame geometry while transferring those loads between successive frames through steel beams instead."
"...Yes. That," Gorthruk said, nodding toward the dragon's head as if this settled the matter entirely.
Arista grinned, delighted by the sheer, unexpected cross-pollination of it, a design meant for one impossible project quietly solving a problem in an entirely different one, the same way so much of her work always seemed to ripple outward into places she'd never originally intended.
"...So the Republic gets safer tunnels, and I get a dome over a drowned mermaid city, all because the same hexagonal frame turned out to be useful for two completely different problems."
"One invention, two applications," Petrov said, already updating his notes accordingly. "That's efficient, at least."
Gorthruk actually smiled at that, small and genuine. "Perhaps your habits are contagious, Strawberry."
"...I'll take that as a compliment."
"It was not entirely intended as one," Gorthruk said, dry. "But it was not entirely not one, either."