Before testing the pressure tap with Korr Var’s liquid silver U-tube, Pella walked the sixty-foot length of the limestone wall to anchor Imran Bell’s six passive indicator tabs into the mortar seams. Each tab consisted of a numbered tin backing plate holding two distinct potion-made-free physical sensors. A strip of litmus parchment treated to blush violet in the presence of formic beetle acid. A recessed groove of crimson-dyed beeswax compounded with stearic animal fat to melt sharply if the surrounding stone ever reached one hundred and thirty-five degrees Fahrenheit.
“Tab Zero-Four goes directly above the baked-clay spreading collar under Arch Four,” Pella said. She pressed the tin lug into the damp lime joint with the flat of her thumb. “Imran tuned the wax mixture in Harrowby using a water bath and a dairy heat gauge. If the stonework heats up during the night when nobody is down here with a lantern, the wax slumps into the lower channel and locks a permanent red streak across the tin.”
The smell of boiling animal fat and hot liquid silver filled the damp gallery of the Ferry Museum twenty minutes before eleven. It drove young Tavi to the head of the iron spiral stair with his sleeve pressed over his nose.
