The first full rib took longer than planned.
It came out of the third zone at the fifth hour of day twenty-one, as the run order on the furnace door said it would. Tavin drew it out on the long tongs and laid it on the fixture to cool, and for a while it looked right. The shoulders dull red, the core and the stepped middle a little brighter, the mirror lining’s stand-in lying flat along the inner face.
Then it began to cool, and the two halves stopped agreeing.
Mara saw it on the thermal trace. The middle cooled first. The water-main alloy gave up its heat quickly, the way Tavin had said it would, the way forty years of terrace mains said it would. But the crown iron shoulders at each end held their glow. Dense metal, slow to cool. And the stepped joins between them, which had carried the heat out so smoothly on the third sample, now carried it the other way: from the hot ends inward, toward a middle that was already cold.
The lining’s stand-in dragged.
She could hear it. Through the graft at its lowest setting, with her hand resting on the bench beside the fixture. A faint grinding, very slow, as the strip along the inner face was pulled one way by the cooling middle and held the other way by the glowing shoulders. A drag, short of a crack, as if the outer grain of the rib and the lining laid…
