Thanks damascus for digging into it a bit deeper, and apologies to Steve for completely missing his comment about charcoal coarseness.
The water? Apparently, the local tap water is just fine for this technique, unless there is a rain catch container, not visible, but distilled water might(?) not be dispensed with a hose. The water quench tank likely has used water in it. I was surprised that copper wiring used to bind some parts, so there may be a higher than normal copper component in the quench water. There were two different charcoal bins, and they appeared to be used in sequence. I'm guessing new material was used around the gun parts, and possibly used charcoal is a filler to top off the crucible, based on possible appearance differences.
