Burden

The blast furnace's charge.

Burden is the packed charge that actually burns in the furnace: ore, fuel and flux combined by the Reinforced Hopper, and nothing a player crafts by hand. It behaves like an ordinary coal pile otherwise, stacking to 128 and laying back down on the ground if it ever spills, and it burns as plain fuel at 600 C if you ever need it to, unspoiled either way. See Ironmaking for what a batch of it costs and yields.