In the modern world, we pick up a bag of charcoal at the market if we want our fires to start easily and get hot quickly. But what did humans from the past do when they wanted their fires to burn hot enough to, say, smelt ore into metal?
I made a batch of charcoal using the mound method then stored it in baskets for later use. Charcoal is a fuel that burns hotter than the wood it’s made from. This is because the initial energy consuming steps of combustion have taken place while making the charcoal driving off the volatile components of the wood (such as water and sap). The result is a nearly pure carbon fuel that burns hotter than wood without smoke and with less flame. Charcoal was primarily a metallurgical fuel in ancient times but was sometimes used for cooking too.
To make the charcoal the wood was broken up and stacked in to a mound with the largest pieces in the center and smaller sticks and leaves on the out side. The mound was coated in mud and a hole was left in the top while 8 smaller air holes were made around the base of the mound. A fire was kindled in the top of the mound using hot coals from the fire and the burning process began.
The fire burned down the inside of the mound against the updraft. I reason that this is a better way to make charcoal as the rising flames have used up the oxygen and prevent the charcoal already made above them from burning while driving out even more volatiles .
I watched the air holes at the base of the mound and when the fire had burned right up to each opening I plugged them with mud. Once all 8 holes had be sealed the hole in the top of the mound was sealed with mud and the mound left to cool.
The next day when the mound was cool to the touch (this can take about 2 days sometimes) I opened the mound. The resulting charcoal was good quality. Some wood near the air entries had burned to ash though these were only small twigs and leaves. This is the reason small brush is put on the out side of the mound, to be burned preferentially to the larger wood on the inside thus protecting the large pieces of charcoal.
In case you missed it: Making a cord drill & pump drill from sticks & rocks.