On the tenth morning at the bellows, the air in the workshop was cold enough to frost the iron poker.
Old Monster Gui stood on the curb of the draft pit, his bronze peg-foot planted beside a crate of thirty honeycomb fuel briquettes. In his left hand he held an ancient bronze water clock with a floating ivory needle. In his right, he gripped a tuned iron measuring rod.
“Today is the final gate,” Gui said, his voice flat and solemn. “A master potion-maker must be able to hold the white flame—the Incandescent Sun—for forty minutes without a single tremor. That’s the heat needed to smelt Dragon-Scale Bark and Gold-Marrow Core. If the heat drops by twenty degrees, the bark hardens into stone. If it climbs by twenty degrees, the gold marrow vaporizes into poisonous gas.”
Gui pointed his iron rod down into the hearth.
“Forty minutes at eleven hundred degrees. Then a stepped descent. Six stages of two minutes each, dropping exactly seventy degrees per stage, landing at four hundred degrees without extinguishing the bed. If you drop the rhythm, if the ivory needle ticks past forty minutes while the flame wanders, you have failed the bellows.”
Pei Jing nodded. “Light the bed.”
