When the outer iron shutter swung back on its heavy pintles, it did not open directly onto an empty chasm.
Set four inches deeper inside the circular bronze housing was an inner pressure window: a disk of smoky mountain quartz three inches thick, beveled around its circumference like a lighthouse lens and clamped into a heavy gunmetal ring by six hexagonal bronze lugs. Even through the darkened crystal and the coat of ancient soot filming its inner face, a fierce, pulsing glare bled into the aqueduct gallery, turning the gray granite walls the color of heated brass.
“Feel the radiant heat coming through three inches of rock crystal,” Alden Bram muttered, holding his calloused palm six inches from the smoked-quartz face before drawing it back with a wince. “If that inner lens weren’t seated in asbestos rope and tallow putty, the draft alone would blister the skin off our cheeks. Wait a breath while I get the double-ended spanner on the trunnion bolts—we don’t drop the glass itself; we swing the outer baffle-frame one notch on the stop-pin so we can clear the soot.”
From his leather mason’s scrip, Bram drew a heavy double-ended iron box-wrench and fitted its jaws over the top bronze lug securing the swivel ring.
