The ceiling came down and the joists were exposed. Big, huge, suckers, each one only a foot apart from another, a great example of old school overengineering. The question was, why is there white stuff on them?
At first, we thought they might be calcium deposits from old leaks, but they're way too uniform and they begin and end at very clear points.
It wasn't until Laclede Gas came out (formerly The Lacled Gaslight Company) to talk about changing our service around that we got a clue. I showed him the ceiling and in turn he showed me a copy of the original service request for the building from 1936 to The Diana Bakery Company. The front of the building was retail, and the rear was the bakery and the white stuff on the joists is 75 YEAR OLD FREAKING FLOUR!