The earliest charcoal pits or stacks were built with the wood lying horizontally, but when the Wallooners (French-speaking Belgians) arrived in the area, they passed on their knowledge of how to build vertical stacks, which were more efficient. Building the stack and then covering it with broken coal and earth required equal measures of skill and care. Once the stack had been lit, the charring process would take two to three weeks.
There was always a danger that trapped gases would cause the stack to flare up suddenly, throwing off the broken coal and earth, with, at worst, the entire stack going up in flames. Voids could also occur, causing collapse of the stack, so the charcoal-burner had to sit watch over the stack continuously, day and night, and be ready to intervene at any time. The charcoal produced from a stack would only be enough to keep the blast furnace fuelled for two days, yet it represented two or three weeks of work for the charcoal-burner. Still, it was absolutely vital that an adequate supply of charcoal was maintained. The stacks were usually sited as close to the smelting house as possible, one reason being that charcoal did not travel well and could easily crumble into unusable dust if shaken up too much during the journey.
The plight of the charcoal-burner, his worries, dreams and folklore, have been highlighted in the poems and songs of Dan Andersson. He was born at Grangärde Finnmark, where there had been a strong tradition of charcoal-burning since the time of the Finnish settlers in the 16th century.