Whether you're surviving in the backwoods or simply camping for the weekend, a fire is essential for heat, light, water purification, and food preparation. Most of us build a campfire around a few large logs, but natural wood isn't always an ideal fuel source. Wood may contain fire-stifling moisture or produce large amounts of smoke; burning some types of wood can even cause lung irritation or blindness.
Charcoal contains minimal moisture, ignites easily, and burns energetically. It also burns hotter and gives off less smoke than raw wood. In a survival situation, you won't be able to buy bags of charcoal briquettes at the grocery store, but with a little time and effort, you can make your own charcoal. You'll just need to build a charcoal kiln.
If you're familiar with the process of making char cloth, the core concept remains the same for charcoal production. You need to expose organic material — in this case, wood — to intense heat inside a container which limits the flow of oxygen. This causes a reaction known as pyrolysis, and leaves a blackened and brittle charred byproduct that can be ignited easily.
In the following video, the host of Primitive Technology shows how to build a simple charcoal kiln from mud. The kiln features eight small air intake holes around the base, and one exhaust vent at the top. The wood pile inside the kiln is ignited through the top hole, and each intake opening is sealed as the fire burns down towards ground level. Finally, the exhaust hole is sealed and the kiln is left to cool overnight. After carefully carving an opening into the side of the kiln, the charcoal can be broken down and removed.