Back to 1888
It’s Pocahontas Number Three coal, from the famous seam in Tazewell County, Virginia, and according to Brendan Burke it is great for blacksmithing.
After Burke moved the coal from the edges of the forge into the firepot, he labored at the blower churning air through the tuyere and into the fire. Green smoke rose from the coals as Burke fed the flames. “The smoke is just weakness leaving the fire,” said Burke. More precisely, impurities, like sulfur, burning off of the coal as it smolders create the green smoke and turn it into coke that is very different from the kind you would drink with your value meal. To a blacksmith, coke is the very high quality source of heat left once the “weakness,” or impurities, burn away.