The cooling tank in Entry hall 722 was a narrow, deep trough carved from a single block of dark andesite, six arm-lengths long and two arm-lengths deep. Filled to the brim with seven-times-filtered deep-sea salt water drawn from the sixty-thousand-fathom trenches of the deep ocean, the water was dark, cold as ice. Then it soaked with stone salts that gave off a sharp, iodine-clean fragrance.
Beside the salt water trough stood a backup basin of sweet limestone spring water, carried down from the cascades of Entry hall 705 to serve as the tempering bath.
Qiao Ming stood between the two basins, his bare horn-hard feet planted firmly upon the wet andesite floor. In his right hand, the long-nosed smithing tongs held the forged needle. The metal had cooled to a deep, dark plum-red—the exact critical heat specified in the metalworking canon of the Broken Slate.
Behind him, Yan Zhiqiu held the horn lantern close to the surface of the salt water trough, her dark eyes calculating the full-body VR angle. “The cool must be upright,” she warned, her voice steady and clear in the quiet vault. “If the needle enters the salt water at an angle, the differential cooling will bow the shaft by three minutes of arc. Plunge it straight along the gravity vector, tip first, and agitate in figure-eight loops for eighteen seconds.”
