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 harder against the wood. The change was subtle but clear. Something was pressing it down that had not existed a moment earlier. From where he sat, he saw no visible boundary to the field and no distortion in the air.
"Can you pull the edge back about six inches?" he asked.
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 while he pushed, paying attention to both movement and pressure. The resistance in his arm increased slightly, then stabilized. When the plate crossed a certain point above the wood, the change stopped.
He lifted his hand and moved it through the air there in a slow arc. Inside the field, pressure pushed back against his palm. A working field applying force. Outside that invisible boundary, there was nothing.
"That's the easy way," she said. "Short range, clean limit."
"What if you switch to pushing instead?"
The field expanded outward. It moved past the end of the bench and reached him where he stood. The pressure arrived against his chest and continued increasing until he stepped backward to reduce it.
"Bigger range," he said. "But what happens to the limit?"
"It leaks," she said. "I can feel the point where it starts flickering." She relaxed the push, and the field shrank back toward the bench.
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 short volume. If he designed the casting floor around that clean range, the compression pass would affect only the molds.
Next he tested intensity. He handed her the iron bar.
"Start from nothing," he said. "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 downwards. 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," she said.
"That point marks the ceiling for precise control."
"If I go past it, I can still produce the force," she said. "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 gap between those numbers was where 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," he said.
She maintained the field. He marked the starting time in the margin and observed.
At ten minutes her breathing had changed. The first visible sign of effort.
At fifteen minutes the iron bar had not changed at all. The field remained stable. He could still feel the limit where he stood, and it had not drifted.
At eighteen minutes he asked, "What does it feel like right now?"
She paused, considering the question. "Like holding something heavy. Possible, but not comfortable."
"If you rested for ten minutes and tried again?"
"I could do it again," she said. "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. He wasn't sure either if their powers repeated in nature.
He noted that separately.
She released the field. The bar returned to its normal position on the bench. She let out a long breath.
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 a specific plan. One of them had been close to the lamp for half an hour and had absorbed some of its heat. He picked that stone up, confirmed 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 and easy to miss without focusing. Heat from the stone moved differently within the gravity field. Instead of rising straight upward, the warm air spread sideways first before dispersing.
He moved his hand slowly through the space above the stone to confirm the observation. Inside the field, the rising heat was redirected. The gravity pressure pushed it outward before it could climb.
He raised his hand above the gravity field. Outside the field, the heat rose normally.
He lowered his hand back inside. 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?" he asked.
"Apparently," she said. "I don't think about it. It just does."
He looked again 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 framework for what he had observed. The fragment in his mind supplied only the outline of a problem. Material behavior under gravity near a heat source. It sounded like a topic that should already exist somewhere in his memory. Something he ought to be able to research.
The fragment offered no more than that awareness.
The question mark remained in the margin. He stared at it for a moment.
The stone had cooled slightly but still had warmth. He returned it to the far end of the bench.
Aestrith had moved and now sat on the corner of the workbench. Her arms hung loosely at her sides. Her gaze stayed fixed on the floor.
"The cook asked about the kitchen supply schedule this morning," he said.
"Why are you telling me that?"
"Because she said you told her to bring the question to me. Apparently you intercepted her in the corridor."
A brief pause.
"She was about to knock on the wrong door," Aestrith said. "I saved you the trouble."
"Right."
He looked at the ledger again. Then at the question mark. Then at the list he had begun beneath it. Items describing the things he still did not understand about the heat behavior he had just seen.
"I'll sort it tomorrow," he said.
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.