She began with the smallest test she could manage.
A gravity field formed over the near end of the bench, covering the iron pieces. The flat plate pressed harder against the wood. The change was subtle but clear. Something was forcing it downward that had not been there a moment earlier. From where he sat, there was no visible boundary to the field and no distortion in the air.
"Can you pull the edge back about six inches?"
She shifted the field.
He stepped off the stool and moved the flat plate slowly toward the new boundary. His hand stayed on the metal as he pushed, paying attention to the movement and the pressure beneath his palm. The resistance in his arm increased slightly, then steadied. When the plate crossed a certain point above the wood, the change stopped.
He lifted his hand and passed it through the air there in a slow arc. Inside the field, pressure pushed back against his palm. Outside that invisible edge, there was nothing.
"That's the easy way," she said. "Short range, clean limit."
"What if you switch to pushing instead?"
The field spread outward. It passed the end of the bench and reached him where he stood. Pressure settled against his chest and kept increasing until he stepped back to ease it.
"Bigger range," he murmured. "But what happens to the limit?"
"It leaks."
She relaxed the push, and the field drew back toward the bench. "I can feel the point where it starts flickering."
He wrote the results down.
Lite mode produced a clean limit but covered less space. Push mode expanded the field but lost precision at the edge.
For the foundry, the mold frames would need to remain entirely inside the shorter volume. If he designed the casting floor around that range, the compression pass would affect only the molds.
Next he tested intensity.
He handed her the iron bar. "Start from nothing. Increase gradually until you reach a normal output. Then keep increasing until precision starts slipping."
She followed the instruction step by step while he watched the bar.
At first nothing changed.
Then the metal pressed downward.
The pressure increased. The wood beneath the bench creaked once she pushed the output higher. That happened somewhere around two thirds of the way to her maximum.
She stopped there.
"There."
"That point marks the ceiling for precise control."
"If I go past it, I can still produce the force." Her eyes stayed on the bar. "But I can't keep it even. Some sections will compress harder than others, and I won't be able to tell from inside the field."
He recorded everything.
The difference between those numbers was where the design decisions belonged. If he operated her at seventy percent of maximum output, maybe slightly less, the castings should remain consistent. If he pushed her higher for speed, the compression would become uneven. That would defeat the entire point of the process.
"Now duration."
She maintained the field while he marked the starting time in the margin and observed.
At ten minutes her breathing had changed. The first visible sign of strain.
At fifteen minutes the iron bar had not shifted at all. The field remained stable. He could still feel the boundary where he stood, and it had not drifted.
At eighteen minutes he looked up from the ledger.
"What does it feel like right now?"
She paused before answering. "Like holding something heavy. Possible, but not comfortable."
"If you rested for ten minutes and tried again?"
"I could do it again. But it wouldn't feel like the first attempt."
He wrote the numbers down.
Eighteen minutes at working intensity before fatigue became obvious. Effort noticeable around the ten minute mark. Ten minutes of rest allowed another run, though shorter for the same quality.
From those figures the rotation schedule practically designed itself. If he ever had more than one Sinbound, he would run them in staggered intervals with recovery between shifts.
He had only one.
And he still was not sure whether their powers repeated in nature.
He noted that separately.
She released the field. The bar settled back into its normal position on the bench. A long breath left her.
He prepared to move on to the next test when he noticed the stone sample.
Three pieces from the wall sat at the far end of the bench, away from the iron. He had left them there without any real purpose. One had been close to the lamp for half an hour and had taken in some of its heat.
He picked the stone up, checked the warmth with his hand, then placed it just inside the gravity field.
He studied the air above it.
Something changed.
The difference was subtle enough to miss without paying attention. Heat from the stone moved differently inside the field. Instead of rising straight upward, the warm air spread sideways before dispersing.
He moved his hand slowly through the space above the stone to confirm it. Inside the field, the rising heat bent outward before it could climb.
He raised his hand above the field.
Outside it, the heat rose normally.
He lowered his hand again. The sideways pressure returned.
He looked at Aestrith.
She had been watching him the entire time, her expression unreadable.
"Does it always behave like that?"
"Apparently." She gave a slight shrug. "I don't think about it. It just does."
He looked back at the stone. Then at his hand. Then at the lamp.
He wrote a short note in the margin of the ledger, drew a line beneath it, and added a question mark.
He did not yet have a way to describe what he had observed. The fragment in his mind offered only the shape of a problem. Material behavior under gravity near a heat source. It sounded like the sort of topic that should already exist somewhere in his memory. Something he ought to be able to research.
The fragment offered nothing more than that faint recognition.
The question mark remained in the margin.
He stared at it for a moment.
The stone had cooled slightly but still held warmth. He returned it to the far end of the bench.
Aestrith had moved while he was writing. Now she sat on the corner of the workbench, her arms hanging loosely at her sides, gaze fixed on the floor.
"The cook asked about the kitchen supply schedule this morning."
"Why are you telling me that?"
"Because she said you told her to bring the question to me." He glanced up from the ledger. "Apparently you intercepted her in the corridor."
A brief silence.
"She was about to knock on the wrong door," Aestrith said. "I saved you the trouble."
"Right."
He looked back at the ledger. At the question mark. Then at the list beneath it, describing the things he still did not understand about the heat behavior he had just seen.
"I'll sort it tomorrow."
Aestrith slid off the bench and walked toward the door without replying.
He did not look up from the ledger until she had already left the room.
The lamp cast steady light across the bench. The iron pieces. The stone that was still faintly warm.
He added another line beneath the question mark.
The list was already longer than he wanted.