The manufacture of charcoal has accompanied both the smelting and forging of metals since the very beginning of metal technologies. Only in the past couple of centuries has it been displaced with fossil fuels, primarily coal and coke. However, on an appropriate scale forging and smelting with charcoal as fuel can be both practical and sustainable. These photographs show two different retort type charcoal making kilns. In retorts, unlike traditional charcoal burning, the wood to be charred is isolated in an airtight vessel, and heated from a separate fire. The gasses that evolve in the pyrolitic process are used to heat the vessel further, which saves fuel and is much cleaner in terms of smoke emissions. In fact, properly fired, the retort does not emit any visible smoke at all. The first six slide show a steel kiln that fires a 55 gallon barrel of wood, in this case birch, which makes excellent charcoal. The inner barrel is loaded, and a small fire built underneath the barrel in the kiln. Gasses from the heated wood are plumbed back into the firebox, so contributing to the efficiency of the process, and burning the volatile matter quite completely in the process. The finished charcoal is ready in about five hours, however the barrel must be cooled before opening. The last three slides show a similar kiln built at Penland School of native clay and rock. It functions much the same except barrels can be inserted and removed more easily without having the entire kiln cool off, making it more efficient and faster.
