James Hubbard, one of several enslaved charcoal-burners, made wood charcoal from dried timber. He stacked 30 cords of wood—3,840 cubic feet—in the shape of a pyramid. Then he covered the wood pyramid with soil or sand to make a kiln. At the base of the kiln, Hubbard lit small fires; the wood charred slowly, with the smoke escaping through openings at the top and bottom. Hubbard, along with other charcoal-burners, monitored his fires closely to prevent them from getting too large and destroying the kiln. After several days, Hubbard scraped off the soil or sand and harvested the charcoal. Most of this charcoal was then stored in the coal sheds on Mulberry Row.