At Fitchburg Furnace, colliers made charcoal from huge piles of charring wood to fuel the furnace. During the summer months, they built many coal pits or hearths throughout the mountains, and a master collier with one or two helpers might work seven to nine pits at a time. Once fired, the pits had to be tended day and night so that the wood would not ignite and burn completely away. Trees marked with orange bands contain about three cords of wood, enough charcoal to fire the furnace for two hours and produce about one cubic foot of pig iron. During the summer, the furnace ran continuously, requiring 30-40 cords of wood from 25-30 year old growth per day. Some furnaces consumed the yield of an acre of woodland a day, and clearcutting went on year-round to provide enough wood for the charring season.