My business was to do the little chores and save time for the helper.

I teased up the furnace, I leveled the fire, I dished the cinders in to thicken the heat, and I watched the cobbles.

During the melting of the pig-iron the furnace had to be kept as hot as coal could make it.
Before the use of coal was discovered, the ancient iron makers used charcoal.

So iron could only be made where there were forests to give fuel.

Even as late as 1840 the iron smelters in Pennsylvania were using wood in their furnaces.