[expand]
Tar production was controlled decomposition—heating wood in limited oxygen so it broke down chemically without completely combusting.
The Loading:
Wood was split to appropriate size—small enough to pack efficiently, large enough that pieces wouldn’t collapse prematurely, sized to provide proper airflow without allowing too much oxygen. The loading pattern mattered—tighter packing at bottom where tar would drain, slightly looser at top to allow gases to escape, arrangement that promoted even heating throughout pile.
The loading could take hours for large kiln—stacking methodically, ensuring stability, packing firmly but not so tightly that nothing could move as wood shrank during heating.
The Ignition:
Fire was started at top—allowing it to burn down gradually through wood pile, creating progression from combustion at top to pyrolysis below. The top layer burned partially—consuming oxygen, generating heat, creating smoke that starved lower layers of air while raising their temperature.
The initial burning phase was critical—establishing proper temperature, creating oxygen-depleted environment, beginning the decomposition that would yield tar.
The Collection:
As wood heated, tar began flowing—liquid droplets forming on hot wood surfaces, running down, accumulating, draining through pile to collection channel. The tar was initially thin, dark brown, becoming thicker and blacker as process continued and temperature-resistant compounds predominated in later flow.
The collection vessel had to be monitored—replacing full containers, ensuring tar didn’t overflow and waste, sometimes filtering or straining to remove particulates. The process continued for days—sustained slow cooking that gradually extracted tar from entire wood pile.
The Completion:
Eventually flow stopped—all extractable tar had drained, remaining wood was charcoal (valuable byproduct for smithing) or ash. The kiln was allowed to cool, contents removed, cycle could begin again with fresh wood load.
[/expand]