The heat reached the hallway before the door was fully open.
The warehouse wing had changed character in the time since they had cleared it. The furnace stood against the far wall, built from stone and lined with clay, with a bellows arm connected to the intake tuyere on the left side of the firebox, the pipe that drove the air blast up through the charge.
Mold frames covered the long table along the opposite wall. Simple iron molds packed in sand, twelve of them arranged in a sequence. Each one corresponded to a crossbow component the garrison currently failed to produce with consistent quality.
Above the furnace, the ceiling beams had already begun to darken from repeated heat cycling.
Wynn stood at the workbench near the furnace with one of his two men, checking the charge ratios by hand. He had been a mine crew foreman before the shafts flooded and the work ended. The knowledge of materials from that job translated well enough to furnace work.
He did not look up when Beorn entered. The charge was at a stage that required focus. Beorn left him to it and crossed to the far end of the room, to the mold table, putting the full working floor between himself and the furnace.
Godric stood at the exterior door. Lewin held position at the internal passage.
Aestrith entered from the secondary corridor that bypassed the main wing approach. The workers used the main entrance. She did not. She came directly to where Beorn stood at the mold table and watched the room from there.
"Nice little place you got here," she said.
"Yes."
"And I'm still the thing nobody in this room can know about." She said it at the same tone as everything else.
The discomfort was real. Beorn chose not to soften it.
"I haven't changed what it is," he said. "I haven't told you otherwise."
She looked at the furnace. "Good. Don't."
The first firing ran through its entire cycle. Wynn managed the bellows rhythm and the charge additions with the concentration of a man who had learned the consequences of bad melt temperature the hard way.
Iron ore went in with charcoal. The blast pushed through the tuyere. The furnace temperature climbed steadily until it reached working heat.
When Wynn called for the pour, his second man opened the tap. Molten iron flowed into the mold frames in a clean, continuous stream. The smell was sharp and mineral, cutting through the already heavy heat in the room.
They waited for the proper casting time.
Then Wynn lifted the first piece.
He ran his thumb along the edge where the cross-section was thinnest. One clean pass. He set it down and picked up the second casting.
The way he held the second piece told Beorn the answer even before Wynn spoke.
"One side cooled differently," Wynn said.
He raised the piece toward the ceiling light.
"Fire side ran hotter. You can see the density fall off here." He tapped the weak section with one knuckle. The sound came back dull.
Beorn already had the ledger open.
Several days earlier, before the furnace had even been built, he had sketched the airflow path in the margin and marked one area as unresolved.
He compared the drawing with the furnace now in front of him. The problem became obvious once he looked for it.
The tuyere sat too far to the left side of the firebox. The air blast overloaded one side of the charge, that side burned hotter, and the melt became uneven long before it reached the molds.
"The intake needs to move to the center," he told Wynn. "The blast is loading the left side of the charge. Center the airflow and the melt evens out."
Wynn examined the tuyere placement, then the interior of the firebox. He verified the logic quickly.
"Will take about an hour."
"Do it."
The crew began removing stone.
Beorn moved to the far end of the room and opened the ledger to a fresh margin. He sketched the revised furnace.
Aestrith leaned against the side wall, watching him.
"You already knew the furnace had a problem?" she said.
"I suspected it." He kept drawing. "Had to find the problem somewhere."
She made a sound that was neither agreement nor disagreement.
"The test was eighteen minutes," she said. She looked at the frames. "This doesn't look like it will take only eighteen minutes."
He gave her the estimated coverage area and the expected duration.
She stayed silent while she evaluated the number.
"That's more than I've tried before," she said.
"I know what I'm asking for."
She looked at him. "Make sure you keep knowing it."
He wrote the duration estimate into the margin.
Beneath it he added another line. The crossbow draw mechanism. The thought surfaced on its own.
The stonework finished slightly over an hour later. Wynn tested the new tuyere position with a short blast and no charge, watching the heat pattern spread through the firebox. He adjusted the left side of the material until the burn pattern balanced.
Second run. Second melt cycle.
When Wynn declared the pour ready, Beorn nodded toward Godric.
"Setting period," Godric said from the door.
Wynn wiped his hands on the rag at his belt and left with his two men. Lewin closed the internal door. Godric secured the exterior entrance.
Now the room held only Beorn, Aestrith, and twelve frames filled with cooling iron.
She stepped forward and evaluated the space. Once she finished that, she let her hands rest at her sides and released the field.
Dust across the work surfaces flattened immediately. Every particle of grit and scale on the wood settled harder into the grain across the entire table.
The heat from the furnace behind them behaved differently inside the field. Instead of rising naturally, it spread outward across the surfaces.
The effect held evenly across the entire row of molds. Each frame carried the same load. Density differences began to level out.
The duration passed ten minutes.
At twelve her breathing changed, slower and deeper.
At fifteen the breathing became controlled effort. The strain was audible.
Beorn recorded the time in the margin and said nothing. She knew her own limits better than anything he could calculate.
When he judged the threshold reached, he said enough.
She released the field.
The room returned to normal conditions with the lingering smell of iron and hot stone.
She exhaled once, fully, and leaned both hands against the edge of the bench. Her eyes stayed closed for several seconds. Then she opened them.
"Don't write down how I looked like," she said.
"I'm writing the time."
"That's not what I meant."
He finished the entry. He didn't look up.
Godric knocked once. Beorn told him to bring the workers back inside.
Wynn walked straight to the table and lifted the first casting. He ran the thumb test along the thin cross-section edge. Same pass as before. He raised the piece toward the light. Then he set it down and picked up the second. Then the third. Then the fourth. Each one received the same examination.
He set the final piece down and looked at Beorn.
"Good work," he said.
He retrieved one of the failed pieces from the first run and held it beside one of the successful castings from the second. The difference was visible even from four feet away. He tapped the good piece with his knuckle and the sound rang clear and solid.
He did not say anything further. By then, Aestrith was already hidden in the far end again. He turned back to the table and began arranging the successful castings for cooling storage.
Aestrith kept silent through the entire time. She had watched Wynn test each piece. When she turned away, her jaw had tightened in a way it had not earlier.
Beorn examined both sets on the table.
The next constraint was already obvious. It remained crude, and the tolerances were still too loose to fully meet the garrison's requirements. That meant at least one or two additional refinement cycles.
He wrote another note. Then one more.
"Part of every afternoon," he said. "Like today."
She looked at the mold frames. Then at the furnace.
"I'll be here," she said.
Beorn picked up the ledger and left the room first.